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Perchlorate Formation by Ozone Oxidation of Aqueous Chlorine/Oxy-Chlorine Species: Role of ClxOy Radicals
Abstract
The environmental occurrence of perchlorate (ClO4(-)) can be related to either natural or anthropogenic sources. Recent studies highlighted the ubiquitous occurrence of natural ClO4(-) in the environment including wet deposition in the United States. Limited studies have investigated potential mechanisms responsible for natural ClO4(-) production in the environment. These studies have neither addressed the influence of relevant reaction conditions nor have they evaluated the rates of ClO4(-) production. The purpose of this study was to determine the comparative yields and rates of ClO4(-) production from O3 mediated oxidation of Cl(-), OCl(-), ClO2(-), ClO3(-), and ClO2. The influence of reactant (O3 and ClOx(-)) concentration and pH were evaluated. The comparative rate and efficiency of ClO4(-) production is generally greater for higher oxidation states of Cl (2.7 to 0.5% for ClO2(-)/ClO2 and 0.02 to 0.005% for OCl(-)/HOCl oxidation) with the notable exception of ClO3(-) which does not react with O3. The very slow rate of ClO4(-) production from Cl(-) ( approximately 20 x 10(-9) mM min(-1)) even at elevated O3 and Cl(-) concentrations implies negligible potential for anthropogenic ClO4(-) formation in process units of water/wastewater systems that use O3 for treatment. Based on results of ClO4(-) formation from tested Cl species and available literature, we propose a potential formation pathway for ClO4(-) from Cl(-) with emphasis on the role of ClO2 and higher oxy-chlorine radicals/intermediates (e.g., Cl2O6) in its formation.
... Documented anthropogenic sources include (1) production as a by-product of paper mills, (2) generation during disinfection processes, (3) application as an herbicide and (4) waste from the industrial production of chlorine dioxide (ClO 2 ) (Pisarenko et al., 2010;Gordon and Tachiyashiki, 1991). Chlorate is also produced through natural processes, as indicated by its widespread occurrence in the environment, similar to ClO 4 À (Rao et al., 2010b;Jackson et al., 2016). ...
... Perchlorate and/or chlorate has been measured in many different environmental settings, including: caliche salts from the Atacama Desert in Chile and the Death Valley area of the Mojave Desert in California; in ice cores, surface soils, and lake samples from Antarctica; in plant extracts from the Mojave Desert; in surface waters throughout the United States; and in wet atmospheric deposition (Rao et al., 2007(Rao et al., , 2010bJackson et al., 2010Jackson et al., , 2012Jackson et al., , 2016Furdui and Tomassini, 2009;Rajagopolan et al., 2006Rajagopolan et al., , 2009. Chlorate has also been detected in meteorites and lunar regolith (Jackson et al., 2015a;Kounaves et al., 2014) suggesting its common occurrence in the solar system. ...
... Chlorate has also been detected in meteorites and lunar regolith (Jackson et al., 2015a;Kounaves et al., 2014) suggesting its common occurrence in the solar system. Reported natural terrestrial ClO 3 À / ClO 4 À ratios are approximately equimolar, with high concentrations of both oxyanions occurring only in semi-arid and arid environments (Rao et al., 2010b;Jackson et al., 2015a, 2015b, 2016(Kounaves et al., 2010. The most abundant chlorine species in the terrestrial environment is chloride (Cl À ), but ClO 4 À and ClO 3 À oxyanions also play an important role in the geochemical cycle of chlorine. ...
Natural chlorate (ClO3⁻) is widely distributed in terrestrial and extraterrestrial environments. To improve understanding of the origins and distribution of ClO3⁻, we developed and tested methods to determine the multi-dimensional isotopic compositions (δ¹⁸O, Δ¹⁷O, δ³⁷Cl, ³⁶Cl/Cl) of ClO3⁻ and then applied the methods to samples of natural nitrate-rich caliche-type salt deposits in the Atacama Desert, Chile, and Death Valley, USA. Tests with reagents and artificial mixed samples indicate stable-isotope ratios were minimally affected by the purification processes. Chlorate extracted from Atacama samples had δ¹⁸O = +7.0 to +11.1 ‰, Δ¹⁷O = +5.7 to +6.4 ‰, δ³⁷Cl = -1.4 to +1.3 ‰, and ³⁶Cl/Cl = 48 x 10⁻¹⁵ to 105 x 10⁻¹⁵. Chlorate from Death Valley samples had δ¹⁸O = -6.9 to +1.6 ‰, Δ¹⁷O = +0.4 to +2.6 ‰, δ³⁷Cl = +0.7 to +1.0 ‰, and ³⁶Cl/Cl = 18 x 10⁻¹⁵ to 49 x 10⁻¹⁵. Positive Δ¹⁷O values of natural ClO3⁻ indicate that its production involved reaction with O3, while its Cl isotopic composition is consistent with a tropospheric or near-surface source of Cl. The Δ¹⁷O and δ¹⁸O values of natural ClO3⁻ are positively correlated, as are those of ClO4⁻ and NO3⁻ from the same localities, possibly indicating variation in the relative contributions of O3 as a source of O in the formation of the oxyanions. Additional isotopic analyses of ClO3⁻ could provide stronger constraints on its production mechanisms and/or post-formational alterations, with applications for environmental forensics, global biogeochemical cycling of Cl, and the origins of oxyanions detected on Mars.
... And the fact that 36 Cl/Cl ratio in dry soils from MDV of Antarctica was among the highest reported for ClO 4 À in soils and caliches from any location also suggests stratospheric source of ClO 4 À (Jackson et al., 2016). Several potential production mechanisms for atmospheric ClO 4 À have been hypothesized including photochemical processes and reactions with O 3 , Cl À and/or chlorine oxide (ClO x ) species (Prasad and Lee, 1994;Kang et al., 2006Kang et al., , 2008Rao et al., 2010). Some of the hypothesized mechanisms have been investigated in experiments simulating natural processes or phenomena, though no natural formation mechanisms have been convincingly established. ...
... NO 3 À is known to form from nitrogen oxides (NO x ) in reactions involving oxidants such as OH free radicals and O 3 (Wolff et al., 2002;Alexander et al., 2009). Naturally occurring ClO 4 À is also believed to form in oxidation reactions in the atmosphere (Bao and Gu, 2004;Jackson et al., 2010), and O 3 is an important oxidant in some proposed ClO 4 À formation mechanisms (Kang et al., 2008;Rao et al., 2010;Jackson et al., 2018). The positive correlation between NO 3 À and ClO 4 À in surface snow suggests that ClO 4 À may be produced in chemical reactions similar to those for NO 3 À formation or that certain key reactants such as O 3 may be common to the formation of ClO 4 À and NO 3 À in the atmosphere over this region. ...
... Along the Zhongshan-Dome A transect, Cl À concentration follows this trend in the first 170 km from the coast and varies slightly in the 170-400 km zone (Fig. 2c). Proposed chemical mechanisms of atmospheric ClO 4 À formation from Cl À include the oxidation of Cl À aerosols, supported by evidence from experiments under simulated lightning conditions (Dasgupta et al., 2005;Rao et al., 2012a), and oxidation of sodium chloride (NaCl) by O 3 (Kang et al., 2008;Rao et al., 2010;Jackson et al., 2018). As discussed above, ClO 4 À in snow in the coastal region is likely dominated by tropospheric production, so can the sea-salt Cl À be a significant precursor of ClO 4 À in the coastal region? ...
Surface snow along a 1250-km transect from the coast to the East Antarctic ice sheet summit Dome Argus are used to investigate factors influencing spatial variability of perchlorate (ClO4⁻) production and deposition, and to explore contributions from tropospheric and stratospheric sources to ClO4⁻ in Antarctic snow. The average ClO4⁻ concentration of 104.3 ± 33.3 ng kg⁻¹ is in the range of previously reported ClO4⁻ concentrations in Antarctic snow, and one to two orders of magnitude higher than those in Arctic snow. The transect profile of ClO4⁻ concentration shows relatively small spatial variability and no single consistent trend, with apparently high concentrations at locations with low accumulation rate. In the coastal region, strong correlation between ClO4⁻ and troposphere-produced nitrate (NO3⁻) is observed. This may indicate that ClO4⁻ in the coastal region is formed predominantly in the troposphere during summer, and the contribution from the stratosphere may be negligibly small. The lack of apparent correlation between ClO4⁻ and NO3⁻ in snow in interior East Antarctica suggests that a significant amount of ClO4⁻ may be of stratospheric origin, with some tropospheric production. No significant correlation is found between sea-salt chloride (Cl⁻) and ClO4⁻ in the coastal region, suggesting that tropospheric sea-salt Cl⁻ is probably not an important precursor of ClO4⁻ in snow in this region. In the inland Dome A region, part of Cl⁻ might be converted into ClO4⁻.
... 21 Perchlorate production has also been demonstrated by O 3 oxidation of aqueous solutions of Cl − , HOCl/OCl − , ClO 2 − , and ClO 2 but was not produced by O 3 oxidation of ClO 3 − . 22 For all ClO x starting species, Cl − and ClO 3 − were the dominant reaction products, while ClO 3 − was the major product with Cl − as the starting species. Perchlorate and ClO 3 − can also be produced in non-aqueous systems by O 3 oxidation of Cl −coated sand or glass. ...
... This is consistent with the presence of Cl − in the flasks at the termination of the experiment and our previous work demonstrating ClO 4 − and ClO 3 − production from aqueous solutions of Cl − , HOCl/OCl − , ClO 2 − , and ClO 2 but not ClO 3 − exposed to O 3 . 22 27 As in previous experiments, no or ClO 3 − was detected in the Na 2 S 2 O 3 trapping solutions but was present in all DDI trapping solutions at concentrations much greater than the detection limits of the Na 2 S 2 O 3 trapping solutions, again indicating production in the trapping solution rather than transport of ClO 3 − or ClO 4 − from the reaction vessel. Chloride was detected (detection limit of 0.5 mg/L) in the DDI water traps at the highest reacted Cl − masses ( The RH was increased to approximately 67% compared to the normal RH of 2% used to conduct our previous experiments. ...
... However, ClO 3 − production (3.65 ± 0.18 μg) in the reactor at elevated RH was approximately 2 orders of magnitude higher than in the dry system (0.069 ± 0.040 μg). Our data are therefore consistent with previous research 22,23 and suggest that even limited water adsorbed on the salt surface supports ClO 3 − formation by a mechanism that does not contribute to ClO 4 − formation. 3.4. ...
The occurrence of chlorate (ClO3-) and perchlorate (ClO4-) in the terrestrial and extra-terrestrial environment has been partly attributed to ozone (O3)-mediated oxidation of chlorine bearing compounds. This is based on varying elevated Δ17O values in all measured terrestrial natural ClO4- as well as the nearly universal co-equal occurrence of ClO3- and ClO4-, which has only been reported to occur for dry oxidation of Cl-, a process for which little information is available. In this study we examine possible factors influencing ClO4- and ClO3- formation by O3 oxidation of sodium chloride (NaCl) salt and hydrochloric acid (HCl) gas in glass reactor vessels. We show that longer reaction times increase production of ClO4- and ClO3-, with ClO3- produced generally being lower than ClO4- by 1-2 orders of magnitude. For 1 day oxidation periods ClO4-/ClO3- ratios were relatively constant (~ 50) for low Cl- masses and decreased over 3 orders of magnitude for higher (~100X) Cl- masses. Perchlorate mass increased with increasing glass reactor surface areas but not salt surface area. Increasing the relative humidity (RH %) from 2 % to 67 % increased ClO3- production, but did not affect the amount of ClO4- produced, confirming previous reports that free water will promote additional ClO3- but not ClO4- production pathways. Additionally, oxidation of HCl (g) produced ClO4- at higher yields than oxidation of NaCl, but produced less ClO3-. Our findings suggest that sufficient O3 saturation and availability of active sites is essential for heterogeneous formation of ClO4- and ClO3-. While glass surfaces per se are not relevant to environmental production, catalytic surfaces (silicate or others) abound in terrestrial and extraterrestrial environments. The Cl- form oxidized and amount of water vapor present will also significantly impact the ClO4-/ClO3- ratio, which could be helpful in evaluating the sources of ClO4- and ClO3- in extra-terrestrial material with important implications on the availability of water during formation.
... The discovery of perchlorate on Mars prompted a renewed interest in how soluble salts are produced on Earth (Rao et al., 2010) and subsequently preserved in desert soils that may serve as viable analogs for Martian landscapes (Ewing et al., 2006;Catling et al., 2010). Perchlorate, a highly soluble anion, interferes with iodide uptake in the human thyroid if ingested at high concentrations (Srinivasan and Viraraghavan, 2009), making the toxic perchlorate levels (~0.3-0.6%) on Mars a challenge for future exploration (Hecht et al., 2009;Leshin et al., 2013). ...
... Perchlorate, a highly soluble anion, interferes with iodide uptake in the human thyroid if ingested at high concentrations (Srinivasan and Viraraghavan, 2009), making the toxic perchlorate levels (~0.3-0.6%) on Mars a challenge for future exploration (Hecht et al., 2009;Leshin et al., 2013). On Earth, perchlorate most likely forms through photochemical reactions with chloride and ozone in the atmosphere (Dasgupta et al., 2005;Rao et al., 2010), yet regional production mechanisms are still under investigation (Jackson et al., 2015). Iodine deficiency is compounded by perchlorate exposure in humans (Leung et al., 2010), rendering iodate, a soluble salt U N C O R R E C T E D P R O O F converted to iodide for use in the thyroid, a health-relevant subject of study (Snyder et al., 2009). ...
... The ∆ 17 O signatures of perchlorate are less documented than nitrate, but suggest a unique isotopic enrichment in the Atacama Desert . On Earth, natural perchlorate forms through atmospheric photochemistry Rao et al., 2010) although specific pathways are still under investigation (Kang et al., 2008;Roberts, 2009;Rao et al., 2012). Conversely, the photochemical production of perchlorate and chlorate on chloride-bearing mineral surfaces may account for a substantial portion of perchlorate accumulation on Mars (Carrier and Kounaves, 2015). ...
Deserts accumulate soluble salts from atmospheric deposition that impact human health, are a source of nutrients for organisms, and provide insight into how landscapes evolved on Earth and Mars. We quantified perchlorate, nitrate, and iodate abundances and co-occurrence in terrestrial deserts to identify fundamental controls on soluble salt deposition and post-depositional cycling. Soils and nitrate deposits were examined in Death Valley, USA; Atacama Desert, Chile; Kumtag Desert, China; and along an environmental gradient in the Transantarctic Mountains, Antarctica. Concentrations of soluble salts were highest in the Atacama Desert and Transantarctic Mountains, where stable, hyper-arid landscapes accumulate atmospheric salts over million-year time scales. Average nitrate concentrations of 53.0 g kg− 1 in the Atacama Desert and 61.3 g kg− 1 in the Transantarctic Mountains were significantly greater than respective averages of 8.60 g kg− 1 and 5.14 g kg− 1 in Kumtag Desert and Death Valley. Perchlorate and iodate concentrations in the Atacama Desert averaged 206 mg kg− 1 and 344 mg kg− 1, respectively, which were two to three orders of magnitude greater than in Antarctica and other sites. Our findings suggest that local processes in the Atacama Desert result either in higher rates of perchlorate and iodate deposition, or a greater preservation of these salts relative to nitrate when compared to Antarctic landscapes. Lower salt concentrations in the Death Valley and Kumtag Desert deposits likely result from relatively wet present-day and paleoclimatic conditions, a more active geologic history, and a greater likelihood that biocycling disrupted long-term salt accumulation. Associations of perchlorate and nitrate were significantly higher than iodate-nitrate and iodate-perchlorate correlations in the four deserts. Perchlorate-nitrate relationships ranged from insignificant to highly significant with stronger correlations in the Atacama Desert and Kumtag Desert compared to the Transantarctic Mountains and Death Valley. Weaker geochemical associations with iodate were attributed to differences in local deposition rates or post-depositional cycling. Interestingly, relationships among perchlorate, nitrate, and iodate were generally stronger when examined by site within each desert compared to analyzing the soils for each desert as a whole, suggesting more localized controls on soluble salt preservation. We conclude that soluble salts vary in concentration and type across Earth's deserts as a result of present-day environment, paleoclimate conditions, biocycling, and geologic age.
... Note that O 3 and OH do not practically convert Cl e to other chlorine species in the bulk solution under the tested conditions (see SDFig. S8 for more information), agreeing with the general finding reported in chemical oxidation processes involving O 3 and OH (Rao et al., 2010; von Gunten, 2003 ). However, once Cl e is electrochemically converted to ClO e and other oxychlorine species (e.g., ClO 2 À ...
... OH can react with these oxychlorines, leading to the formation of ClO 3 À (see SDFig. S9 and refer to (Nicoson et al., 2002; Rao et al., 2010; von Gunten, 2003 )). In addition, oxychlorine species (e.g., HClO/ClO e and ClO 2 À ...
... However, as manifested by the results of divided cell tests, ClO 3 À cannot be further converted to ClO 4 À via chemical oxidation with O 3 and OH or via interactions with other chlorine species in the bulk solution (see SDFig. S10 and refer to (Czarnetzki and Janssen, 1992; Gordon and Tachiyashiki, 1991; Rao et al., 2010; von Gunten, 2003)). Therefore, it is concluded that the conversion of ClO 3 À to ClO 4 À must involve the participation of the anode to electrochemically convert ClO 3 À firstly to ClO 3 , which can then react with OH to yield ClO 4 À (Azizi et al., 2011). ...
This study investigated the degradation of clofibric acid and formation of perchlorate during the electro-peroxone (E-peroxone) treatment of chloride-containing (26.1-100 mg L(-1)) water (Na2SO4 electrolytes and secondary effluents). The E-peroxone process involves sparging O2 and O3 gas mixture into an electrolysis reactor where a carbon-based cathode is used to electrochemically convert the sparged O2 to H2O2. The electro-generated H2O2 then reacts with sparged O3 to produce OH, which can rapidly oxidize pollutants in the bulk solution. When boron-doped diamond (BDD) electrodes were used as the anode, perchlorate concentrations increased significantly from undetectable levels to ∼15-174 mg L(-1) in the different water samples as the applied current density was increased from 4 to 32 mA cm(-2). In contrast, no ClO4(-) was detected when Pt/Ti anodes were used in the E-peroxone process operated under similar reaction conditions. In addition, when sufficient O3 was sparged to maximize OH production from its peroxone reaction with electro-generated H2O2, the E-peroxone process with Pt/Ti anodes achieved comparable clofibric acid degradation and total organic carbon (TOC) removal yields as that with BDD anodes, but did not generate detectable ClO4(-). These results indicate that by optimizing operational parameters and using Pt/Ti anodes, the E-peroxone process can achieve the goal of both fast pollutant degradation and ClO4(-) prevention during the treatment of chloride-containing wastewater.
... For the solid-gas heterogeneous reactions (described above), mineral characteristics are the primary control. In the additional NaCl solution-O 3 experiments, ClO 3 − is predominant over ClO 4 − regardless of the type of Fe mineral (Extended Data Fig. 4d), consistent with previous solution experiments 11,12 . Gaseous Cl − probably follows different reaction pathways from solid or aqueous Cl − (ref. ...
... In comparison, ClO 3 − is more geochemically active than ClO 4 − . While remaining stable under neutral to alkaline pH, aqueous ClO 3 − can decompose under acidic conditions, and the formed ClO 2 may lead to additional ClO 3 − and ClO 4 − formation 12 . Chlorate can also be reduced by Fe 2+ and organics but would not be reduced by active carbon 41 . ...
Perchlorate (ClO4⁻) and possibly chlorate (ClO3⁻) are considered to be ubiquitous on Mars1–5, and the ClO3⁻/ClO4⁻ abundance ratio has critical implications for the redox conditions6,7, aqueous environments8,9 and habitability on Mars¹⁰. However, factors that control the ClO3⁻/ClO4⁻ generation ratios are not well established. Here we expose mixtures of halite salt (NaCl) with Fe sulfates, Fe (hydr)oxides and Fe³⁺ montmorillonite to ultraviolet radiation or ozone in an Earth or CO2 atmosphere and show that Fe secondary mineralogy is the dominant factor controlling the ClO3⁻/ClO4⁻ generation ratio: the sulfates and montmorillonite mixtures produce much higher yields of ClO4⁻ than of ClO3⁻, whereas the opposite is true for the (hydr)oxide mixtures. Consistent with previous studies11–18, our results indicate that the physical state of chloride (Cl⁻) (that is, solid, liquid or gas) and the characteristics of the co-occurring minerals (for example, semiconductivity, surface area, acidity) have the greatest influence, whereas oxidation sources (ultraviolet radiation or ozone) and atmospheric composition induce only secondary effects. We conclude that, under the hyperarid climate and widespread Fe (hydr)oxide abundances prevailing on Mars since the Amazonian period¹⁹, Cl⁻ oxidation should produce yields of ClO3⁻ that are orders of magnitude higher than those of ClO4⁻, highlighting the importance of ClO3⁻ in the surficial environments and habitability of modern Mars compared with ClO4⁻.
... Natural resources of perchlorate are found in abnormal condition. Perchlorate produce by serial reaction in environment involving electrical discharge lighting, oxidation of ozone and UV exposure [24], [26], [27].The perchlorate has also produce by natural sources through photochemical reaction in the environment including inorganic chlorine with ozone [24] and organic chlorine species like methyl chlorine which converted into a inorganic species [25]. After that it contributes to make perchlorate in stratosphere. ...
... Natural resources of perchlorate are found in abnormal condition. Perchlorate produce by serial reaction in environment involving electrical discharge lighting, oxidation of ozone and UV exposure [24], [26], [27].The perchlorate has also produce by natural sources through photochemical reaction in the environment including inorganic chlorine with ozone [24] and organic chlorine species like methyl chlorine which converted into a inorganic species [25]. After that it contributes to make perchlorate in stratosphere. ...
Perchlorate is a highly toxic compound. It has both chemical and physical properties. Perchlorate is not easily degradable compound by both bio and non-bio degradation process because of its high stability, highly water soluble compound and low absorption. That's why perchlorate reduction becomes a big challenge. In this research work we studied different type of electrochemical technique and effect of different electrodes on these techniques. In present days, many techniques were developed for the detection or reduction of perchlorate such as bio-degradation, optical, chemical, electrochemical and microbial technique. This article gives information about application of electrochemical technique for the detection or reduction of perchlorate. The electrochemical techniques have various types for the detection of ion. These techniques grouped on the behalf of various types of electrical signal such as potential or voltage, current and impedance which were produce in the presence of perchlorate into aqueous solution. Electrochemical technique such as impedance spectroscopy, this technique was performed on the electrochemical work station by applied a constant range of frequency. In cyclic voltammetry technique we were given a constant potential range and found results in the form of oxidation and reduction current. In the reduction of perchlorate history various researcher was found results using different electrochemical technique on different types of electrodes. The perchlorate salts and perchlorate have some useful application in the defense field, batteries, automobile airbags, rocket propellants and fuels. Perchlorate contamination is become a worldwide health problems. In many western states perchlorate was found in ground and surface water. It disturbs the thyroid gland to uptake iodine the human body. So its prevention technique was needed. However, the electrochemical techniques have more advantage such as low cost, user friendly, label free and real time monitoring over all other techniques. So we focus on electrochemical detection technique for the perchlorate.
... Atmospherically produced ClO 4 − may come from both the troposphere and the stratosphere. Proposed chemical mechanisms of atmospheric ClO 4 − formation in the troposphere suggest that Cl − is the most likely initial precursor (Furdui and Tomassini, 2010;Furdui et al., 2018), and ozone (O 3 ) and hydroxide radical (OH radical) may be the dominant oxidants (Prasad and Lee, 1994;Dasgupta et al., 2005;Kang et al., 2008;Rao et al., 2010;Jackson et al., 2018). Regression analysis shows that there is no significant correlation (r = − 0.05, p = 0.87; n = 12) between the concentrations of Cl − and ClO 4 − in this region. ...
... Antarctic total column ozone (TCO) varies seasonally, with significant depletion of stratospheric O 3 over Antarctica (Antarctic ozone hole) between September and October since 1980s (Farman et al., 1985;World Meteorological Organization., 2018). O 3 is an important oxidant in some proposed ClO 4 − formation mechanisms (Kang et al., 2008;Rao et al., 2010;Jackson et al., 2018), therefore, variation of O 3 concentration may result in seasonal variation of ClO 4 − . According to the sub-annual time scale of WAIS Divide snow, the annual ClO 4 − minimum generally occurs in September-October when column ozone reaches the lowest levels, which indicates that stratospheric O 3 depletion may influence ClO 4 − production in the atmosphere (Jiang et al., 2016;Crawford et al., 2017). ...
Perchlorate (ClO4⁻) is harmful to human health, and knowledge on the levels and sources of natural ClO4⁻ in different environments remains rather limited. Here, we investigate ClO4⁻ in aerosol samples collected along a cross-hemisphere ship cruise between China and Antarctica and on a traverse between coastal East Antarctica and the ice sheet summit (Dome Argus). Perchlorate concentrations range from a few to a few hundred pg m⁻³. A clear latitudinal trend is found, with elevated ClO4⁻ concentrations near populated areas and in the southern mid-high latitudes. Spatial patterns of atmospheric ClO4⁻ over oceans near the landmasses support that terrestrial ClO4⁻ is not transported efficiently over long distances. In the southern mid-latitudes, higher ClO4⁻ concentrations in March than in November-December may be caused by significant stratospheric inputs in March. Perchlorate concentrations appear to be higher in the warm half than in the cold half of the year in the southern high latitudes, suggesting seasonal difference in main atmospheric sources. ClO4⁻ may be formed in the reactions between chlorine free radical (Cl·) and ozone (O3) in the stratosphere when Antarctic ozone hole occurs during September-October. And the stratosphere-produced ClO4⁻ is moved to the boundary layer in several months and may be responsible for the high ClO4⁻ concentrations in the warm half of the year. Perchlorate produced by photochemical reactions between O3 and Cl· in the Antarctic stratosphere is likely responsible for the higher ClO4⁻ concentrations in Antarctica than in Arctic.
... However, the additional presence of ClO 3 − in the Phoenix soil could not be precluded as the Ion Selective Electrode on Phoenix is about 1,000 times more sensitive to perchlorate than to chlorate and therefore any signal from chlorate can be masked by perchlorate (Hanley et al., 2012). Chlorate is a stable intermediate oxychlorine species which generally coexists with perchlorate on Earth (Kounaves et al., 2014;Rao, Anderson, et al., 2010), often in higher concentration (Jackson, Bohlke, et al., 2015), and is thus expected to coform with perchlorate on Mars. Both perchlorate and chlorate are believed to be present in Gale crater sediments as indicated by the Sample Analysis at Mars instrument on Mars Science Laboratory (Ming et al., 2014;Stern et al., 2017;Sutter et al., 2017). ...
... Oxychlorine species are produced by both atmospheric and surface processes (Catling et al., 2010;Georgiou et al., 2017;Kim et al., 2013;Schuttlefield et al., 2011;Wilson et al., 2016) which should yield a wide planetary distribution that impacts the global Cl cycle. Several detections of oxychlorine species (Jackson, Davila, et al., 2015;Rao, Hatzinger, et al., 2010) and their possible formation pathways (Carrier & Kounaves, 2015;Jackson et al., 2018;Kim et al., 2013;Quinn et al., 2013;Rao, Anderson, et al., 2010;Zhao et al., 2018) report chlorate presence in either an equimolar or greater ratio to perchlorate. Therefore, chlorate is an essential Cl species on the Martian surface along with perchlorate (Kounaves et al., 2014;Stern et al., 2017;Sutter et al., 2017). ...
Oxychlorine species are globally widespread across the Martian surface. Despite their ubiquitous presence, the ability of oxychlorine species to serve as oxidants on Mars has largely been unexplored. While perchlorate is kinetically inert, chlorate may be a critical Fe (II) oxidant on Mars. However, the time scale over which chlorate may oxidize Fe (II) and the mineral products formed in Mars‐relevant fluids are unclear. Fe (II) oxidation by chlorate was thus investigated in magnesium chloride, sulfate, and perchlorate fluids under neutral to acidic conditions for different total Fe (II) and background salt concentrations. The results show near‐complete Fe (II) oxidation within approximately 2 to 4 weeks, accompanied by formation of the Fe (III) minerals goethite, lepidocrocite, akaganeite, and jarosite. The Fe (II) oxidation rate and the mineral product depend on Fe (II) concentration, the composition and concentration of the background salt, and the acidity of the solution. Calibration of an existing rate law to lower temperatures well reproduces the observed oxidation kinetics in all fluid compositions and allows prediction of the rate of Fe (II) oxidation by chlorate under diverse Mars‐relevant conditions. Rate comparisons demonstrates that chlorate can oxidize Fe (II) substantially faster than O2 and on similar or shorter timescales than ultraviolet (UV) light. Notably, chlorate causes rapid oxidation under acidic conditions, unlike other oxidants. Chlorate may thus represent an important abiotic Fe (II) oxidant on Mars. The expected co‐association of chlorate with perchlorate may allow for its percolation into the subsurface during brine migration, leading to oxidation in regions that are cut‐off from UV radiation and atmospherically‐derived oxidants.
... Band engineering and doping modification methods for bulk g-C 3 N 4 can allow the generation of % OH in the VB and improve the photocatalytic oxidation activity of g-C 3 Therefore, devising methods to produce % OH at both the CB and VB of a photocatalyst could lead to very powerful oxidative reactivity. Besides % OH, chlorine-based ions (e.g., ClO − , ClO 2 − , ClO 3 − ) with high oxidation activity have also been extensively studied in advanced oxidation techniques for water treatment [36][37][38][39]. Considering the stronger oxidative reactivity of % OH than some chlorine-based ions [36,37], such chlorine-based species may also be involved in photocatalytic systems. ...
... Ultimately, these chlorine-based oxidizing species produced from the % OH-induced reactions could promote the removal of pollutants. This could be the reason why S/Cl-CN displayed the best photocatalytic activity among the S/halogen-codoped g-C 3 N 4 samples, and is consistent with a previous report that chlorate-based ions exerted the best oxidation ability among halogenbased ions [39]. ...
Elemental doping is an important strategy for modifying the electronic properties of graphitic carbon nitride and tuning its visible-light photocatalytic activity. In this study, sulfur- and chlorine-co-doped g-C3N4 (S/Cl-CN) have been synthesized by a thermal condensation method. Among a series of samples, S/Cl-CN exhibited the best photocatalytic activities for the degradation of rhodamine B (RhB) and 4-nitrophenol (4-NP). The as-synthesized S/Cl-CN possessed a modified electronic structure and large specific surface area as well as more active sites. According to diffuse-reflectance spectroscopy (DRS), UPS (ultraviolet photoelectron spectrometer), and valence band (VB)-XPS investigations, S/Cl-CN displayed a narrowed band gap and positively shifted VB edge potential with enhanced oxidation ability. First-principles calculations implied that the narrower band gap and better charge-separation ability may be attributed to the Cl 3p orbital as the doping level. Moreover, the S/Cl-CN with narrowed band-gap and positively shifted VB potential could possess double channels to form OH by direct oxidation of h⁺ at VB and reduction of O2 at CB. Based on the strong oxidizing ability of the S/Cl-CN, the possible formation of reactive chlorine-based species in the photocatalysis process is proposed. This work provides a new perspective for tuning the band structure of a photocatalyst through a doping strategy and greater insight into the generation paths of active species involved in the photocatalytic process.
... [10][11] On Earth natural perchlorate (often accompanied by chlorate) is ubiquitously formed in the atmosphere and widely distributed by both wet and dry deposition. [12][13] It is typically found at higher concentration levels in arid locations across the globe such as, the Atacama Desert (Chile), 14 the McMurdo Dry Valleys (Antarctica), 15 the Mojave Desert (USA), 16 the Tindouf Basin (Morocco), 17 and many others. 18 It has also been shown to be present on the Moon, the Murchison and Fayetteville chondrite meteorites, and likely across the entire solar system. ...
... 22 Laboratory experiments have demonstrated a number of potential ClO 4 production mechanisms, including O 3 and Clreactions in aqueous systems, 12, 23 by electrolysis, 24 lightning discharges, 20 UV irradiation of Clsolutions and oxide minerals, 25 and photodecomposition of aqueous chlorine solutions. 12,26 Chlorate and chlorite (ClO 2 -) have also been produced under irradiation by 5 keV electrons. 27 However, none of them are likely to be occurring under the severely arid Mars ambient conditions (i.e., -40°C to 5°C, 96% CO 2 and 0.1% oxygen, ~10 Torr). ...
The widespread presence of perchlorate (ClO4⁻) on Mars has significant implications for the alteration or destruction of indigenous organic compounds that may have been or still be present on Mars. The intermediary products of the UV-driven production of ClO4⁻ include oxychlorines (ClOx) such as chlorite (ClO2⁻), chlorate (ClO3⁻), and chlorine-dioxide (ClO2) gas. The objective of this study was to start with ClO2⁻ or ClO3⁻ under Mars ambient and vary temperature, humidity, and UV wavelengths, in order to isolate the reaction pathways leading to ClO4⁻. We also investigated the role of titanium dioxide (TiO2) as a catalyst for these reactions. We show here that the production of ClO4⁻ from ClO2⁻ and ClO3⁻ proceeds through different pathways. The ClO2⁻ is rapidly converted to stable levels of ClO3⁻ and Cl⁻, suggesting that the amount present on Mars will likely be very low compared to other ClOx. We also observed that temperature does not affect ClO4⁻ production when starting with NaClO2 but causes a decrease in ClO4⁻ production when starting with NaClO3, and that production of ClO4⁻ using UV >300 nm with O2 present, does not involve an ozone (O3) pathway. We have also shown that adding TiO2 to the SiO2/ClOx mixture has a catalytic effect in the production of ClO4⁻ under terrestrial conditions but shows primarily a shielding effect under Mars ambient; that ClO3⁻ is stable under Mars ambient even in the presence of TiO2 and is not affected by temperature or humidity. Finally, it was shown that water is necessary for generation of ClO2(g) during perchlorate production from either NaClO2 or NaClO3. This suggests that production of ClO2 might be occurring on Mars in areas where ice can provide increased humidity levels.
... Previous research (Dasgupta et al. 2005, Sturchio et al. 2009, 2016 has suggested that a significant fraction of the total perchlorate is of natural origin, probably produced in the atmosphere involving photolysis and/or oxidation of common chlorine species, which is supported by recently published work (Peterson et al. 2015a(Peterson et al. , 2015b. Both laboratory measurement (Kang et al. 2008, Rao et al. 2010) and analysis of trends of perchlorate in the environment (Furdui & Tomassini 2010, Jackson et al. 2015a) demonstrate that ozone is involved in atmospheric perchlorate production by oxidation. In addition to formation in the stratosphere (Jackson et al. 2015a(Jackson et al. , 2016, perchlorate may also be produced in the troposphere through photolysis and heterogeneous reactions (Dasgupta et al. 2005, Kounaves et al. 2010) and lightning (Furdui & Tomassini 2010, Rao et al. 2012. ...
... The data show that perchlorate production is reduced when stratospheric ozone concentrations are low. Ozone concentrations can impact perchlorate production because ozone can be a key reactant in the perchlorate formation reactions (Rao et al. 2010). If the atmospheric production of perchlorate over Antarctica, and in general in the polar regions, occurs primarily in the stratosphere, rather than the troposphere (Sturchio et al. 2009, Furdui & Tomassini 2010, the lowered stratospheric ozone concentrations would result in reduced perchlorate concentration in spring snow. ...
Snowpit samples collected at the West Antarctic Ice Sheet (WAIS) Divide location in January 2013 were analysed to investigate the levels and variations of perchlorate concentrations in Antarctic snow. During 2008–12, the perchlorate concentration in WAIS Divide snow ranged between 6–180 ng l –1 and followed a seasonal cycle. The highest concentrations appeared in the autumn, and the lowest in winter and spring. No apparent correlation was observed between perchlorate and nitrate or chloride concentrations in snow. Since perchlorate is believed to form in the atmosphere when chlorine species are oxidized in reactions involving ozone, perchlorate concentrations were hypothesized to be high during the spring, based on the assumption that stratospheric ozone depletion enhances tropospheric perchlorate production. The data show that perchlorate concentrations in snow were sharply reduced during stratospheric ozone depletion events; the evidence, therefore, does not support the hypothesis. Instead, the results suggest a stratospheric origin of perchlorate in Antarctic snow.
... It has been suggested that the heterogeneous reaction of O 3 on chloride-containing aqueous and salt surfaces constitutes a potential formation mechanism of ClO 3 − and ClO 4 − (refs. [25][26][27] ). However, the formation of HClO 3 and HClO 4 via heterogeneous reactions on the aerosol surface or direct emission from the surface of snowpacks is likely not the dominant pathway in the Arctic. ...
Chlorine radicals are strong atmospheric oxidants known to play an important role in the depletion of surface ozone and the degradation of methane in the Arctic troposphere. Initial oxidation processes of chlorine produce chlorine oxides, and it has been speculated that the final oxidation steps lead to the formation of chloric (HClO3) and perchloric (HClO4) acids, although these two species have not been detected in the atmosphere. Here, we present atmospheric observations of gas-phase HClO3 and HClO4. Significant levels of HClO3 were observed during springtime at Greenland (Villum Research Station), Ny-Ålesund research station and over the central Arctic Ocean, on-board research vessel Polarstern during the Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC) campaign, with estimated concentrations up to 7 × 10⁶ molecule cm⁻³. The increase in HClO3, concomitantly with that in HClO4, was linked to the increase in bromine levels. These observations indicated that bromine chemistry enhances the formation of OClO, which is subsequently oxidized into HClO3 and HClO4 by hydroxyl radicals. HClO3 and HClO4 are not photoactive and therefore their loss through heterogeneous uptake on aerosol and snow surfaces can function as a previously missing atmospheric sink for reactive chlorine, thereby reducing the chlorine-driven oxidation capacity in the Arctic boundary layer. Our study reveals additional chlorine species in the atmosphere, providing further insights into atmospheric chlorine cycling in the polar environment.
... Ion perchlorate is present in the Antarctic environment and is part of the ionic composition of the snow, firn, and ice 51 . It is postulated a stratospheric origin for the perchlorate, assuming that chemical targets are present as gaseous chlorine, O 3 , and OH radicals 28,29,52 . The ClO 4is one of the substances that contribute to the photochemical process of ozone loss in the Antarctic stratosphere (i.e., it could be generated when short wave UV-B radiation (<200 nm) interacted with chlorofluorocarbon molecules at the surface of polar stratospheric clouds (PSCs), which then reacted with ozone 52 ). ...
Since the early 1980s, the Antarctic environment has served as a natural field laboratory for researchers to investigate the effects of stratospheric ozone depletion, which has resulted in increased surface ultraviolet radiation levels. However, its effective threats still present gaps. We report new pieces of evidence of increased ultraviolet radiation impacting West Antarctica sea salt aerosols. Salt aerosols, particularly in the Southern Ocean Sea, play an important role in the radiative earth balance. To disclose the molecular details of sea salt aerosols, we used a synchrotron-based multi-element microscopic speciation of individual microparticles (Scanning Transmission X-ray Microscopy with Near-Edge X-ray Absorption Fine Structure Spectroscopy combined with Computer-Controlled Scanning Electron Microscopy). Here we identified substantial abundances of chlorine-enriched aerosols in sea salt generated by photolytic products, whereas ice core records revealed increased chlorine depletion from the onset of ozone depletion. Our findings reveal that modern sea salt modification has no Holocene precedent.
... 32 While reactions between chlorine (HOCl/OCl − ) and ozone via free radical pathways can lead to the formation of chlorate in low-DOC water, the very slow rate of perchlorate production from Cl − even at high concentrations of O 3 and Cl − implies negligible potential of perchlorate formation in water/ wastewater treatment processes involving ozone. 33 This is because O 3 interacts with Cl − very slowly (k = 2.2 × 10 −3 M −1 S −1 at 20°C, pH > 3) to produce OCl − for chlorate and perchlorate generation. 34 Although cOH may react with Cl − and lead to the Cl 2 c − intermediate for chlorate formation, the product (ClOH − ) of the starting reaction has a high dissociation rate constant (Cl − + OH 4 ClOH − , k f = 4.3 × 10 9 M −1 S −1 , k r = 6.1 × 10 9 M −1 S −1 ), 35 resulting in limited chlorate production under water/ wastewater relevant conditions (e.g. ...
Heterogeneous catalytic ozonation (HCO) is a promising advanced oxidation process (AOP) that can effectively degrade recalcitrant organic pollutants; but formation of harmful byproducts should be carefully evaluated.
... Other species are ineffective or implausible oxidants of Mn(ii) in subsurface fracture systems. Hydrogen peroxide (H 2 O 2 ) reduces Mn(iii/iv) to Mn(ii) 34 ), hypochlorite (ClO − ) and chlorine dioxide (ClO 2 ) gas as well as an array of radicals, are probably produced as short-lived intermediates on Mars 42,43 and are known to rapidly oxidize dissolved Mn(ii) 44,45 . However, their non-detection on Mars 20 indicates that they do not accumulate on the surface, unlike more oxidized species, and their transient nature in water 46 suggests that they may decompose before reaching subsurface fracture systems where manganese oxides formed 1,2,4 . ...
In situ rover investigations on Mars have discovered manganese oxides as fracture-filling materials at Gale and Endeavour craters. Previous studies interpreted these minerals as indicators of atmospheric oxygen on early Mars. By contrast, we propose that the oxidation of manganese by oxygen is highly unlikely because of exceedingly slow reaction kinetics under Mars-like conditions and therefore requires more reactive oxidants. Here we conduct kinetic experiments to determine the reactivity of the oxyhalogen species chlorate and bromate for oxidizing dissolved Mn(ii) in Mars-like fluids. We find that oxyhalogen species, which are widespread on the surface of Mars, induce substantially greater manganese oxidation rates than O2. From comparisons of the potential oxidation rates of all available oxidants (including reactive oxygen species peroxide and superoxide), we suggest that the oxyhalogen species are the most plausible manganese oxidants on Mars. In addition, our experiments precipitated the manganese oxide mineral nsutite, which is spectrally similar to the dark manganese accumulations reported on Mars. Our results provide a feasible pathway to form manganese oxides under expected geochemical conditions on early Mars and suggest that these phases may record an active halogen cycle rather than substantial atmospheric oxygenation. Manganese oxidation experiments in Mars-like fluids suggest that chlorate and bromate may have been more effective oxidants of manganese on early Mars than atmospheric oxygen and explain observed manganese oxide deposits.
... Concomitantly, H 2 O 2 (produced at the cathode) may react with the chlorinated species. This reaction can be either of reduction or oxidation, depending on the solution pH [51]. ...
An electro-peroxone (EP) process was conducted in an up-flow bubble column reactor with BDD electrodes. The efficiency of the process was tested in the 4-Chlorophenol (4-CPh) mineralization and compared with that attained by single treatments like ozonation (O3) and electro-oxidation (EO). At [TOC]o= 56 mg·L⁻¹, pHo= 7.0, T = 293 K, j = 0.06 A·cm⁻², t = 120 min, the oxidation power decreased in the following order EP>EO>O3, and the TOC removed was, in the same order, 100%> 93%> 40%. The calculated synergy coefficient was 0.31, while the mineralization current efficiency percentage (MCE%) and the energy consumption (EC) were 12.24% and 11.48%, 2.84 and 2.31 kW·h⁻¹, for EP and EO, respectively. The germination percentage of Lactuca sativa, was 100%, 30% and 20%, at the end of EP, EO and O3, respectively. This indicates that phytotoxicity, was only eliminated with EP. Based on the by-products, e.g. aromatic compounds (4-chlorocatechol, catechol, phenol, p-benzoquinone, hydroquinone) and carboxylic acids (maleic, formic, fumaric, succinic, oxalic, malonic and acetic acids) identified by UHPLC-UV/DAD and the changes of the concentration of chloride ion (Cl⁻), hypochlorite, chlorite, chlorate and perchlorate, a reaction pathway was proposed for the 4-CPh mineralization by the E-peroxone process. It was demonstrated that under the studied conditions both, hydrogen peroxide and ozone, are produced during EO. At the end of EO, H2O2, carboxylic acids and perhaps persulfates, are responsible for the phytotoxicity of the solution.
... Perchlorate (ClO -4 ) is an ubiquitous contaminant, which is naturally occurring in the environment but also released from anthropogenic sources (solid rocket propellants, munitions, fireworks, airbag initiators for vehicles, matches, and signal flares). Natural formation of perchlorate in the atmosphere [4] and precipitation in surface water, could contribute to the presence of perchlorate in food as well [5]. However, the main potential sources of contamination are soil and groundwater contaminated as a result of industrial emissions or the use of certain natural fertilizers (i.e. ...
In this study an analytical procedure, based on a modification of the so-called QuPPe-method (quick method for the analysis of numerous highly polar pesticides in food), has been evaluated for routine monitoring of chlorate and perchlorate in a broad range of food matrices. Analytes were extracted with a mixture of water, acidified methanol and dichloromethane, followed by liquid chromatography tandem mass spectrometry (LC-MS/MS) determination. For LC separation HILIC stationary phase provided best results in terms of robustness and column durability. Quantification was performed by isotopic dilution, using the respective ¹⁸O isotopically labelled analogues as internal standards. The method was validated in four Nestlé Quality Assurance Centres (NQACs) according to the current EU guidelines for pesticides method validation (SANTE/12682/2019). Trueness of the method ranged from 91.3 to 110.1 %, and intermediate precision was lower than 20 %, except for slight deviations observed in two matrices. Limits of quantification (LOQs) of the method were 0.010 mg/kg for chlorate and perchlorate in all matrices, except for perchlorate in food intended for infants for which the LOQ was 0.002 mg/kg, thus equal or below the maximum residue levels (MRLs) specified on the current EU regulations and recommendations. Therefore, the method fits for monitoring in high routine environments at those decision levels.
... The kinetics and mechanism of ClO -3 formation during ozonation have been extensively studied (Jung et al., 2017;Kang et al., 2008;Levanov et al., 2019Levanov et al., , 2008Rao et al., 2010). Its formation mechanism is divided into three pathways: i) direct pathway ( ...
The prevalence of organic micropollutants (OMPs) in aquatic environment has expedited scientific and regulatory efforts to retrofit existing wastewater treatment plants (WWTPs). The current strategy involves WWTPs upgrading with post-ozonation i.e., ozone (O3) and/or peroxone process (O3+H2O2). Still, ozone-based degradation of OMPs faces several challenges. For example, the degradation mechanism and kinetics of OMPs could largely be affected by water matrix compounds which include inorganic ions and natural organic matter (NOM). pH also plays a decisive role in determining the reactivity of the oxidants (O3, H2O2, andHO•), stability and speciation of matrix constituents and OMPs and thus susceptibility of OMPs to the reactions with oxidants. There have been reviews discussing the impact of matrix components on the degradation of OMPs by advanced oxidation processes (AOPs). Nevertheless, a review focusing on scavenging mechanisms, formation of secondary oxidants and their scavenging effects with a particular focus on ozonation and peroxone process is lacking. Therefore, in order to broaden the knowledge on this subject, the database ‘Web of Science’ was searched for the studies related to the ‘matrix effect on the degradation of organic micropollutants by ozone based processes’ over the time period of 2004-2021. The relevant literature was thoroughly reviewed and following conclusions were made: i) chloride has inhibitory effects if it exits at higher concentrations or as free chlorine i.e. HOCl/ClO−. ii) The inhibitory effects of chloride, bromide, HOBr/OBr− and HOCl/ClO− are dominant in neutral and alkaline conditions and may result in the formation of secondary oxidants (e.g., chlorine atoms or free bromine), which in turn contribute to pollutant degradation or form undesired oxidation by-products such as BrO3–, ClO3– and halogenated organic products. ii) NOM may induce inhibitory or synergetic effects depending on the type, chemical properties and concentration of NOM. Therefore, more efforts are required to understand the importance of pH variation as well as the effects of water matrix on the reactivity of oxidants and subsequent degradation of OMPs.
... Laskin et al. 46 attributed the Cl decrease to emissions of molecular chlorine to the gas-phase, while they proposed the formation of NaOH in the particulate phase due to reactions with OH radicals. Another possibility for the appearance of O is the formation of chlorates 55,56 . By overlapping the signals for Na and Cl a depletion of Cl can be seen primarily at the surface of the particles ( Fig. 4c; Exp. 2). ...
Sea spray aerosol (SSA) contributes significantly to natural aerosol particle concentrations globally, in marine areas even dominantly. The potential changes of the omnipresent inorganic fraction of SSA due to atmospheric ageing is largely unexplored. In the atmosphere, SSA may exist as aqueous phase solution droplets or as dried solid or amorphous particles. We demonstrate that ageing of liquid NaCl and artificial sea salt aerosol by exposure to ozone and UV light leads to a substantial decrease in hygroscopicity and cloud activation potential of the dried particles of the same size. The results point towards surface reactions on the liquid aerosols that are more crucial for small particles and the formation of salt structures with water bound within the dried aerosols, termed hydrates. Our findings suggest an increased formation of hydrate forming salts during ageing and the presence of hydrates in dried SSA. Field observations indicate a reduced hygroscopic growth factor of sub-micrometre SSA in the marine atmosphere compared to fresh laboratory generated NaCl or sea salt of the same dry size, which is typically attributed to organic matter or sulphates. Aged inorganic sea salt offers an additional explanation for such a measured reduced hygroscopic growth factor and cloud activation potential.
... Any chlorate present in Phoenix soil samples might therefore be masked in the presence of perchlorate [57]. Terrestrial field studies of oxychlorine salt occurrences and laboratory investigations of their formation processes indicate that chlorate should generally co-form with perchlorate in equimolar or greater proportions [58][59][60]. Chlorate is therefore likely to be an important Cl-bearing species that is widespread on the surface of Mars, but our knowledge of its occurrence is limited by the lack of ability to detect this species in many past landed missions. While chlorate likely always co-occurs with perchlorate, the latter displays no reactivity towards Fe(II) [49,61,62] and is not relevant to iron chemistry on the Martian surface. ...
Chlorate is an important Cl-bearing species and a strong potential Fe(II) oxidant on Mars. Since the amount of oxychlorine species (perchlorate and chlorate) detected on Mars is limited (<~1 wt.%), the effectiveness of chlorate to produce iron oxides depends heavily on its oxidizing capacity. Decomposition of chlorate or intermediates produced during its reduction, before reaction with Fe(II) would decrease its effective capacity as an oxidant. We thus evaluated the capacity of chlorate to produce Fe(III) minerals in Mars-relevant fluids, via oxidation of dissolved Fe(II). Each chlorate ion can oxidize 6 Fe(II) ions under all conditions investigated. Mass balance demonstrated that 1 wt.% chlorate (as ClO3−) could produce approximately 6 to 12 wt.% Fe(III) or mixed valent mineral products, with the amount varying with the formula of the precipitating phase. The mineral products are primarily determined by the fluid type (chloride- or sulfate-rich), the solution pH, and the rate of Fe(II) oxidation. The pH at the time of initial mineral nucleation and the amount of residual dissolved Fe(II) in the system exert important additional controls on the final mineralogy. Subsequent diagenetic transformation of these phases would yield 5.7 wt.% hematite per wt.% of chlorate reacted, providing a quantitative constraint on the capacity of chlorate to generate iron oxides on Mars.
... Perchlorate occurs naturally in the environment in deposits of nitrate (caliche) and can be formed in the atmosphere and precipitate into soil (Ericksen 1981). Chilean sodium nitrate deposits (caliche) are known to contain naturally occurring perchlorate (Calderón et al. 2014;Urbansky et al. 2001;Rao et al. 2010). Several studies have reported perchlorate concentrations in nitrate minerals and fertilizers produced in the Atacama Desert ranged from N.D. to 5.7 g kg -1 and 0.5 to 4 g kg -1 , respectively (Ericksen 1981;Dasgupta et al. 2005). ...
Perchlorate (ClO4−) has been identified as a persistent environmental contaminant of concern. Perchlorate exposure is a potential health concern because it interferes with hormone production by thyroid gland. Food (fruits and vegetables) and drinking water are an important source of human exposure to perchlorate. However, little is known about the occurrence of perchlorate in Chile. The purpose of this study was to determine the occurrence of perchlorate in 145 samples (soil, drinking water, surface water, groundwater, fertilizers, fruits and vegetables) collected across Chile and estimate associated exposure to consumers. Our results show that perchlorate was detected in soil (median: 22.2 ng g−1), drinking water (median: 3.0 ng mL−1), fruits (median: 0.91 ng g−1 fresh weight [FW]), lettuce (median: 5.0 ng g−1 FW) and chard (median: 4.15 ng g−1 FW). Interestingly, perchlorate concentrations detected in drinking water from three regions (Serena, Copiapo and Illapel) exceeded the USEPA interim drinking water health advisory level of 15 ng mL−1. Median concentrations of perchlorate in non-nitrogenous fertilizers (3.1 mg kg−1) were higher than those in nitrogenous fertilizers (1.3 mg kg−1). Estimated daily intake (EDI) of perchlorate via drinking water was lower than the USEPA’s reference dose (7000 ng kg−1 bw day−1). The EDI of perchlorate via vegetables (chard and lettuce) produced in northern Chile was three times higher than those produced in other regions. The results of this study provide information about perchlorate sources in Chile, which will be helpful in modifying current regulations.
... However, the formation of OCl − due to reaction 21 is subordinated, as only 30% of the formed product yields OCl − 71 . It should be noted, though, that, in other publications 72,73 , especially in Liu et al. 74 , this pathway is mentioned as the main formation pathway of OCl − . Hence, dissolved O 3 , as a gaseous precursor of other oxidizing molecules in a plasma treated liquid, is of great relevance for plasma liquid chemistry in the context of biomedical applications of plasmas, especially for jet-like plasmas where a strong stirring of the liquid occurs. ...
In the field of plasma medicine, the identification of relevant reactive species in the liquid phase is highly important. To design the plasma generated species composition for a targeted therapeutic application, the point of origin of those species needs to be known. The dominant reactive oxygen species generated by the plasma used in this study are atomic oxygen, ozone, and singlet delta oxygen. The species density changes with the distance to the active plasma zone, and, hence, the oxidizing potential of this species cocktail can be tuned by altering the treatment distance. In both phases (gas and liquid), independent techniques have been used to determine the species concentration as a function of the distance. The surrounding gas composition and ambient conditions were controlled between pure nitrogen and air-like by using a curtain gas device. In the gas phase, in contrast to the ozone density, the singlet delta oxygen density showed to be more sensitive to the distance. Additionally, by changing the surrounding gas, admixing or not molecular oxygen, the dynamics of ozone and singlet delta oxygen behave differently. Through an analysis of the reactive species development for the varied experimental parameters, the importance of several reaction pathways for the proceeding reactions was evaluated and some were eventually excluded.
... Perchlorate also is formed by natural photochemical processes (Dasgupta et al., 2005;Kang et al., 2006Kang et al., , 2008Rao et al., 2010). While these natural formation processes result in the widespread presence of perchlorate in the environment, the levels are typically below those thought to present a health concern. ...
This paper reviews the unique situation of perchlorate contamination in Chile, including its sources, presence in environmental media and in the human population, and possible steps to mitigate its health impacts. Perchlorate is a ubiquitous water contaminant that inhibits thyroid function. Standards for drinking water range from 2 to 18 µg L-1in United States and Europe. A major natural source of perchlorate contamination is Chile saltpeter, found in the Atacama Desert. High concentrations of perchlorate have presumably existed in this region, in soils, sediments, surface waters and groundwaters, for millions of years. As a result of this presence, and the use of Chile saltpeter as a nitrogen fertilizer, perchlorate in Chile has been found at concentrations as high as 1480 µg L-1in drinking water, 140 µg/kg-1in fruits, and 30 µg L-1in wine. Health studies in Chile have shown concentrations of 100 µg L-1in breast milk and 20 µg L-1in neonatal serum. It is important to acknowledge perchlorate as a potential health concern in Chile, and assess mitigation strategies. A more thorough survey of perchlorate in Chilean soils, sediments, surface waters, groundwaters, and food products can help better assess the risks and potentially develop standards. Also, perchlorate treatment technologies should be more closely assessed for relevance to Chile. The Atacama Desert is a unique biogeochemical environment, with millions of years of perchlorate exposure, which can be mined for novel perchlorate-reducing microorganisms, potentially leading to new biological treatment processes for perchlorate-containing waters, brines, and fertilizers.
... It is a highly oxidized (+7) oxyanion that both naturally and anthropogenically occurs in the atmosphere (1,2). Perchlorate can originate from natural atmospheric reactions involving ozone, solar energy, hypochlorite, or chloride during lightening discharges (3,4). Recently, Kounaves et al. (5) reported perchlorate concentrations up to 1100 µg/kg in soils from Antarctic dry valleys, suggesting the natural formation of perchlorate. ...
Perchlorate (ClO₄(−)) is an environmental pollutant thataffects human health. Perchlorate acts as a competitive inhibitor of iodine uptake in the thyroid gland (sodium–iodide symporter inhibitor); thus, its determination is important for public health concerns. Water and milk constitute a significant portion of the human diet. Because regular intake leads to an increase in perchlorate concentration in the human body, the estimation of perchlorate is of great concern. In this work, ion-pair single-drop microextraction (SDME) combined with attenuated total reflectance (ATR)-FTIR spectroscopy has been developed for the determination of perchlorate in bioenvironmental (soil, water, dairy milk, breast milk, and urine) samples. Perchlorate was extracted in a single drop of methyl isobutyl ketone as an - with the cationic surfactant cetyltrimethylammonuim bromide under optimized conditions. The strongest IR peak (at 1076 cm(−1)) was selected for the quantification of perchlorate among three observed vibrational peaks. Eight calibration curves for different concentration ranges of perchlorate were prepared, and excellent linearity was observed for absorbance and peak area in the range of 0.03–100 ng/mL perchlorate, with r values of 0.977 and 0.976, respectively. The RSDs (n = 8) for the perchlorate concentration ranges of 0.03–100, 0.03–0.5, 0.5–10, and 10–100 ng/mL were in the range of 1.9–2.7% for the above calibration curves. The LOD and LOQ in the present work were 0.003 and 0.02 ng/mL, respectively. The extracted microdrop was analyzed directly by ATR-FTIR spectroscopy. The parameters affecting SDME, i.e, effect of pH, stirring rate, reagent concentration, microdrop volume, and extraction time, were optimized, and the role of foreign species was also investigated. F- and t-tests were performed to check the analytical QA of the method. A noteworthy feature of the reported method is the noninterference of any of the associated ions. The results were compared with those of the ion chromatography MS method, and a high degree of acceptability was found. The method was successfully applied for the determination of perchlorate in bioenvironmental samples.
The coordinated removal of pollutants in wastewater, especially metal ions and organic pollutants, is regarded as a tough challenge and has focused wide attentions. Synergistic photocatalytic-photothermal route is a powerful technology for the potential wastewater treatment. Herein, we designed a synergistic photocatalytic-photothermal system based on two-dimensional Ti3C2Tx MXene (TCM) membrane for simultaneous recovery of Ag⁺ ions and removal of aqueous rhodamine B (RhB). The photo-reduction of Ag⁺ ions into Ag nanoparticles with the conversion rate up to 100% was achieved on TCM membrane under visible-light irradiation. These Ag nanoparticles uniformly deposited on the surface and interlayers of TCM membrane. It facilitated the separation of photo-generated charges for forming more active species, including both ∙O2⁻ and ∙OH radicals, to oxide RhB molecular. At the same time, the surface plasma effect of Ag nanoparticles enhanced the light adsorption and photothermal conversion efficiency (~81%) on the TCM membrane. Conversely, photothermal effect was beneficial for further enhancing the reaction rate of both reduction of Ag⁺ ions and photo-oxidation of RhB by concentrating the solution and promoting the electron transfer. The novelty of the synergistic photocatalytic-photothermal contribution is significant for simultaneous recovery of metal ions and removal of organic pollutants in wastewater.
The Antarctic environment has been used as a natural field laboratory to investigate the impacts of enhanced UV-B radiation over the polar terrestrial biota, marine life, and the cryosphere. UV-B increased levels occur due to the stratospheric ozone depletion detected since the early 80s’ decade. The real dimension of the ozone depletion threat to the Antarctic environments and the atmospheric chemistry remains uncertain. This work presents new pieces of evidence of this impact on individual aerosol particles sampled in West Antarctica, using a synchrotron-based multi-element microscopic/molecular speciation method. We used the Scanning Transmission X-ray microscopy with Near-Edge X-ray Absorption Fine Structure Spectroscopy combined with Computer-Controlled Scanning Electron Microscopy to identify the molecular changes in sea salt particles due to photolytic processes involving chlorine-enriched particles during the ozone depletion period since the 80´s decade. Combining our data with ice core records, we deduce that the modern effects of UV-B on the tropospheric chlorine geochemistry have no precedent for the Holocene.
Chlorine has important roles in the Earth's systems. In different forms, it helps balance the charge and osmotic potential of cells, provides energy for microorganisms, mobilizes metals in geologic fluids, alters the salinity of waters, and degrades atmospheric ozone. Despite this importance, there has not been a comprehensive summary of chlorine's geobiology. Here, we unite different areas of recent research to describe a biogeochemical cycle for chlorine. Chlorine enters the biosphere through volcanism and weathering of rocks and is sequestered by subduction and the formation of evaporite sediments from inland seas. In the biosphere, chlorine is converted between solid, dissolved, and gaseous states and in oxidation states ranging from −1 to +7, with the soluble, reduced chloride ion as its most common form. Living organisms and chemical reactions change chlorine's form through oxidation and reduction and the addition and removal of chlorine from organic molecules. Chlorine can be transported through the atmosphere, and the highest oxidation states of chlorine are produced by reactions between sunlight and trace chlorine gases. Partial oxidation of chlorine occurs across the biosphere and creates reactive chlorine species that contribute to the oxidative stress experienced by living cells. A unified view of this chlorine cycle demonstrates connections between chlorine biology, chemistry, and geology that affect life on the Earth.
The role of hydroxyl radicals (OH) as a daytime oxidant is well established on a global scale. In specific source regions, such as the marine boundary layer and polluted coastal...
The magnetic biochar catalyst ([email protected]) was synthesized by pyrolyzing Fe–tanned collagen fiber based on the tanning process and used as a high–efficiency and recyclable persulfate (PS) activator to degrade refractory dyes. In this study, methylene blue (MB) was chosen as a model pollutant to evaluate the performance of the [email protected]/PS system. Results illustrated that MB was completely removed within 20 min with a rate constant (kobs) of 0.2246 min–1, which was much higher than that of pure biochar (0.0497 min–1), and high mineralization efficiency (92%) for MB degradation was obtained. Notably, the MB removal rate still reached 72% after 20 cycles. The high catalytic activity and excellent recycling performance could be attributed to the uniformly dispersed iron species, abundant oxygen functional groups, and defective carbon matrix. Radical quenching experiments and electron paramagnetic resonance studies illustrated that SO4•– was the predominant free radical for MB degradation. Moreover, other refractory dyes could also be rapidly and efficiently removed from the [email protected]/PS system. This work is expected to propose a promising catalyst for the degradation of refractory dyes and open a new possibility for the durable removal of refractory organic dyes.
The contents of perchlorate and chlorate were determined in a total of 278 samples of infant formulas marketed in China. The associated health risk via infant and young child formulas consumption for 0–36 month old children in China was also assessed. The contents of perchlorate and chlorate were measured by a validated method with LC-MS and the limit of detection (LOD) was 1.5 μg kg⁻¹ and 3.0 μg kg⁻¹ for perchlorate and chlorate, respectively. Perchlorate and chlorate were detected in about 85.8% (median 6.92 μg kg⁻¹, maximum 74.20 μg kg⁻¹) and 99.3% (median 52.80 μg kg⁻¹, maximum 2780 μg/kg) of the samples. The exposures of infant and young children to perchlorate from formulas were lower than the provisional maximum tolerable daily intake (PMTDI, 0.7 μg/kg bw/day), which was established by U.S. Environmental Protection Agency (EPA). The European Food Safety Authority (EFSA) in 2015 also proposed a tolerable daily intake (TDI) of 3 μg/kg bw/day for chlorate based on the mean and average concentrations. Only for infants 0–6 month at the 95th percentile did exposures exceed the TDI of 3 μg/day for chlorate. Therefore, the safety of infant and young child formulas is excellent. To our knowledge, this is the first report to assess the exposure of infant and young child formulas in China to perchlorate and chlorate.
Perchlorate (ClO4⁻), a persistent inorganic compound, has harmful effects on human health. Natural ClO4⁻ is formed in the atmosphere and enters into the surface environment through deposition. However, the knowledge on the occurrence, spatial variability and sinks of natural ClO4⁻ in different environments remains limited, especially in the polar regions. Here, we investigate the sources and sinks of ClO4⁻ in soil collected in three ice-free areas in coastal Antarctica, where the research stations and wildlife colonies are mainly distributed. No statistically significant difference in ClO4⁻ concentrations between sites near and away from the stations suggests that local human presence is not a significant source of ClO4⁻ in soil. Concentrations of ClO4⁻ in soil from wildlife colonies are not significantly higher than those from sites with no intense wildlife activities, indicating that wildlife activities have no significant influences on ClO4⁻ in soil. Thus, atmospherically formed ClO4⁻ is the main source for soil in Antarctica. In general, ClO4⁻ concentrations (0.1–5.1 μg kg⁻¹) in soil in this study are much lower than those in the arid environments and comparable to those in the unsaturated zones. Leaching by snow meltwater may be the main sink for ClO4⁻ in soil, and deeper depths for aqueous migration may contribute to the lower ClO4⁻ concentrations in Antarctic surface soil compared to the values in the arid areas with low precipitation amount. Due to the biological origin of NO3⁻, no correlation between NO3⁻ and ClO4⁻ in soil is observed in this study, different from the observations in arid areas. In addition, no significant correlation is observed between organic matter contents and ClO4⁻ concentrations in soil, suggesting that biological reduction is not an important sink for ClO4⁻ in Antarctic soil.
Natural perchlorate (ClO4⁻) exists in many places on Earth, in lunar regolith, meteorites, and on the surface of Mars. Terrestrial natural ClO4⁻ has widely variable Cl and O stable isotopic compositions (δ³⁷Cl, δ¹⁸O, Δ¹⁷O). The δ¹⁸O and Δ¹⁷O values of ClO4⁻ from the most hyper-arid locations co-vary. ClO4⁻ from less arid areas has relatively little ¹⁷O excess and poor Δ¹⁷O-δ¹⁸O correlation. ClO4⁻ from the Atacama Desert has unusually low δ³⁷Cl (< -10‰) and exhibits a positive correlation between δ³⁷Cl and δ¹⁸O, while the δ³⁷Cl of ClO4⁻ from all other locations varies between -5 and +7 ‰ with no δ³⁷Cl-δ¹⁸O covariation. To evaluate the impact of different precursors (ClOx) and reaction pathways on the isotopic composition of ClO4⁻, we measured the isotopic composition of ClO4⁻ produced in the laboratory by UV or O3 mediated aqueous oxidation of Cl⁻, OCl⁻, ClO2⁻, and ClO2° as well as O3 mediated oxidation of dry NaCl. ClOx oxidation in aqueous or dry systems enriched in O3 produced ClO4⁻ with Δ¹⁷O values that generally increased with the number of O atoms required and included evidence that the site-specific ¹⁷O anomaly in O3 was preferentially transferred to ClO4⁻. Based on the inferred number of O atoms sourced from O3, and known Cl and O reaction pathways, it appears that ClO2° and ClO3* were required intermediates in the production of ClO4⁻ in the O3 experiments. ClOx aqueous oxidation by UV irradiation produced ClO4⁻ with a large range of δ¹⁸O values and little or no ¹⁷O anomaly. ClO3⁻ was produced to a much greater extent than ClO4⁻ in all experiments except dry oxidation of NaCl by O3. The isotopic composition of ClO3⁻ was distinct from that of ClO4⁻ produced from the same initial reactants. Combined results of O3 and UV mediated reactions largely bracketed the range of natural ClO4⁻ δ¹⁸O and Δ¹⁷O values as well as δ³⁷Cl values of non-Atacama natural samples, but no conditions produced the low δ³⁷Cl values of Atacama ClO4⁻. Our results indicate that variation in production mechanisms, possibly combined with isotopically variable precursors, could be responsible for much of the observed isotopic variation in natural ClO4⁻ and ClO3⁻.
Phosphate buffered saline (PBS) is a commonly used medium for in vitro experiments in plasma biomedicine; however, the mechanism for changes in PBS in response to plasma treatment is not well understood. Many kinds of reactive species are produced in plasma-activated PBS, but to date only a few of them can be quantified. In this paper, therefore, we aim to develop a fully coupled model for the interaction between surface air plasma and PBS, primarily to quantify its plasma-induced aqueous reactive species, as well as to elucidate their production mechanism. This model consists of a 0D sub-model for the surface plasma in air, and two 1D sub-models: for the PBS, and for the air gap between the plasma and the PBS. Similar models have been reported by our group fwith respect to the plasma treatment of deionized water. Here, by comparison, an additional 24 chlorine compounds, 17 phosphorous species and 123 chemical reactions are incorporated in our model. Our results indicate that the main aqueous reactive species are H 2 O 2aq , O 3aq , NO 2aq ⁻ , NO 3aq ⁻ , HClO aq , ClO 2aq and ClO 3aq ⁻ . During plasma treatment, the oxidation reduction potential of most reactive species increases within the first 50 s, then remains almost constant. The chemical profile of the plasma-activated PBS is also plotted, from which it can be observed that some reactive oxygen species, such as OH aq , H 2 O 2aq , and O 3aq play a crucial role in the production of chlorine compounds such as HClO aq and ClO 3aq ⁻ .
The efficient removal of ammonia is a difficult issue in wastewater treatment because ammonia is easily converted to nitrate instead of N2. The oxidation of ammonia by chlorine radical (Cl•) is recognized as an effective method. However, the massive generation of toxic byproducts chlorate and nitrate pose great risk for its practical application due to the excessive oxidation capacity of hydroxyl radical. Herein, we propose a novel method to selectively generate Cl• for efficient ammonia removal using BiVO4/WO3 photoanode in a self-driven photoelectrocatalytic (PEC) system. Cl• was predominantly produced by regulating the valence band edge of WO3 though modifying BiVO4, which tuned the moderate oxidative force of hole to reduce OH• generation and thereby inhibited the formation of chlorate and nitrate. The self-driven ammonia degradation was achieved by employing BiVO4/WO3 and Si photovoltaic cells as composite photoanodes to improve light-absorption and electron-hole separation, thus enhancing Cl• production. These results showed that 10 mg L⁻¹ of ammonia-N was completely removed (99.3%) in 120 min with 80.1% of total nitrogen removal. Toxic byproducts chlorate and nitrate were inhibited by 79.3% and 31%, respectively, compared to WO3. This work provides new insights to develop efficient, energy-saving and environment-friendly method for ammonia pollution treatment.
A mechanism (a set of significant reactions with rate constants) has been proposed for the complex chemical reaction of ozone with chloride ion in aqueous solution at pH 5.5 - 12, leading to the formation of the main product chlorate ion ClO3–, and perchlorate ion ClO4– as a by-product. A mathematical model of chemical reactions kinetics in the O3 - Cl–(aq) system has been constructed. The most important chlorate formation channels are initiated by oxidation of chloride ion with ozone molecule or hydroxyl free radical. The reaction of Cl– with O3 leads to the formation of hypochlorite ion in the primary stage. Subsequent oxidation reactions of ClO– give chlorine dioxide ClO2˙ as an intermediate. When chloride is oxidized with OH˙ radicals, Cl2˙− anion-radicals are formed, which then react with ozone to form chlorine monoxide ClO˙. Subsequent oxidation and combination reactions of ClO˙ and ClO2˙ and the hydrolysis of complex chlorine oxides Cl2Ox lead to the generation of chlorate and also perchlorate. The results obtained quantitatively characterize for the first time the complex reaction of O3 with Cl–(aq) based on the mechanism, and make it possible to predict the kinetics of its products formation under various conditions.
The results of studies of a complex chemical reaction of ozone with chloride ions in aqueous solution, in crystalline salts, and in aerosol are generalized and systematized; its kinetics and mechanism are discussed. The role of the reaction in various industries, in particular, in water treatment, and in natural processes is considered.
The discovery of abundant perchlorate (ClO4⁻) on Mars has prompted renewed interest in the production, accumulation and transport of ClO4⁻ and other oxychlorine species in natural systems. Here we focus on the role of semiconducting minerals in the photochemical generation and destruction of ClO4⁻ and chlorate (ClO3⁻). Illumination of single crystal, or nanocrystalline films, of titanium dioxide polymorphs - rutile and anatase - in chloride (Cl⁻) solutions can both generate and destroy ClO4⁻ depending on starting ClO4⁻ and Cl⁻ concentrations. For single crystal anatase, we observe an apparent photostationary state in which ClO4⁻ production and destruction reach a near-steady state. We observe more ClO3⁻ production and less ClO4⁻ at higher Cl⁻ concentrations. An inventory of measured dissolved chlorine (Cl) species indicates that some Cl was lost to a volatile form or to a dissolved form not measured. Our experiments were performed in an aqueous medium under Earth atmosphere and temperature conditions; further experiments under Mars-like conditions are in progress. Photochemical processes as described here, in which activation energy is provided by photons, are particularly important under cold conditions with limited thermal activation. KEYWORDS: perchlorate, Mars, photochemistry, titanium dioxide, chlorine chemistry
Chlorate ion ClO 3⁻ is formed as a result of the complex chemical interaction of ozone with chloride ion in aqueous solution. In neutral and basic solutions, chlorate is the main product. In acid solutions, the main product is molecular chlorine Cl 2 , and the yield of chlorate is 50–100 times lower. Dependencies have been studied of chlorate formation rate on significant experimental factors: concentrations of initial substances, ozone and chloride ion, acidity (pH), ionic strength and temperature of the reaction solution. The kinetic laws of chlorate generation have been established, and the expressions are given for rate constants of chlorate formation as functions of temperature and ionic strength. When tert-butanol is added to the reaction system, the formation of chlorate ceases, which is an evidence of the crucial role of free radical reactions in this process.
Recent investigations have reported a widespread occurrence of chlorate (ClO3⁻) and perchlorate (ClO4⁻ ) throughout the solar system including terrestrial arid environments. ClO3⁻ and ClO4⁻ are deposited/accumulate at an approximate equal molar ratio with some exceptions such as the Antarctica dry valley soils (MDV) and perhaps Martian surface material, where ClO4⁻ is the dominate ClOx⁻ species. All known ClO4⁻ production mechanisms produce molar ratios of ClO3⁻ : ClO4⁻ equal to or much greater than 1, suggesting that reduced ratios may be due to post depositional mechanism(s). The objective of this study was to investigate potential iron-mediated abiotic reduction of ClO3⁻, similar to transformation mechanisms reported for nitrate (NO3⁻) by Fe (II) minerals. Three types of Fe (II)-containing minerals wustite (FeO), siderite (FeCO3), and sulfate green rust (GRSO4²⁻) were investigated in completely mixed batch reactors as potential ClO3⁻ reductants at a range of pH (4 - 9) and iron mineral concentrations (1 to 10 g/L). ClO3⁻ was stoichiometrically reduced to chloride (Cl⁻) by wustite, siderite, and green rust, but no transformation occurred by dissolved Fe (II). Wustite and green rust reduced NO3⁻ but not by siderite. When both NO3⁻ and ClO3⁻ are reduced simultaneously, ClO3⁻ is reduced preferentially to NO3⁻, although the effect is somewhat concentration dependent. Increased background salt concentration (NaCl) increased ClO3⁻ reduction but decreased NO3⁻. The stability of ClO3⁻ and subsequent impacts on the ratio of ClO3⁻ : ClO4⁻ in the environment have implications for understanding the cycling of oxyanions and stability of iron minerals and related to this, the ratio of ClO4⁻ and ClO3⁻ may be an indicator of the past availability of free water. On Mars, these reactions may help to explain the unusually high concentrations of ClO4⁻ compared to ClO3⁻ and NO3⁻.
A 300-year (1700-2007) chronological record of environmental perchlorate, reconstructed from high-resolution analysis of a central Greenland ice core, shows that perchlorate levels in the post-1980 atmosphere were two-to-three times those of the pre-1980 environment. While this confirms recent reports of increased perchlorate in Arctic snow since 1980 compared with the levels for the prior decades (1930-1980), the longer Greenland record demonstrates that the Industrial Revolution and other human activities, which emitted large quantities of pollutants and contaminants, did not significantly impact environmental perchlorate, as perchlorate levels remained stable throughout the eighteenth, nineteenth, and much of the twentieth centuries. The increased levels since 1980 likely result from enhanced atmospheric perchlorate production, rather than from direct release from perchlorate manufacturing and applications. The enhancement is probably influenced by the emission of organic chlorine compounds in the last several decades. Prior to 1980, no significant long-term temporal trends in perchlorate concentration are observed. Brief (a few years) high concentration episodes appear frequently over an apparently stable and low background (~1 ng kg‒1). Several such episodes coincide in time with large explosive volcanic eruptions including the 1912 Novarupta/Katmai eruption in Alaska. It appears that atmospheric perchlorate production is impacted by large eruptions in both high and low latitudes, but not by small eruptions and non-explosive degassing.
Halogen-rich minerals containing at least one halogen (F, Cl, Br or I) on a dominant crystallographic site can be divided into three broad groups: (1) halides, (2) halogenates, and (3) native halogens. There are approximately 700 halogen-rich minerals in the 09/2014 list of species approved by the International Mineralogical Association (IMA), accounting for ~15% of the entire mineral kingdom known to date. Still scores of other minerals contain significant amounts of F and/or Cl, especially in many hydrous minerals via the copious substitution (F,Cl)⁻ = OH⁻. Amphiboles, micas and apatites are the dominant carriers of halogens in most rocks, whereas scapolites and sodalites serve as important hosts of these elements in some exotic lithologies. These minerals not only play important roles in controlling the halogen geochemical cycles but also are useful for calcuating the halogen composition and evolution of fluids/melts from which they crystallized.
An ice core of 15.5 meters retrieved from Agassiz Ice Cap (Nunavut, Canada) in April 2009 was analyzed for perchlorate to obtain a temporal trend in the recent decades and to better understand the factors affecting High Arctic deposition. The continuous record dated from 1936 to 2007, covers the periods prior to and during the major atmospheric releases of organic chlorine species that affected the stratospheric ozone levels. Concentrations and yearly fluxes of perchlorate and chloride showed a significant correlation for the 1940-1959 period, suggesting a predominant tropospheric formation by lightning. While concentration of chloride remained unchanged from 1940s until 2009, elevated levels of perchlorate were observed after 1979. A lack of significant increases in either sulfate or chloride between 1980 and 2001 suggests that the effect of volcanic activities on the perchlorate at the study site during this period could be insignificant. Therefore, the elevated perchlorate in the ice could most likely be attributed to anthropogenic activities that influenced perchlorate sources and formation mechanisms after 1979. Our results show that anthropogenic contribution could be responsible for 66% of perchlorate found in the ice. Although with some differences in trends and amounts, deposition rate found in this study is similar to those observed at Devon Island (Nunavut, Canada), Eclipse Icefield (Yukon, Canada) and Summit Station (Greenland). Methyl chloroform, a chlorinated solvent largely used after 1976, peaked in the atmosphere in 1990 and has a much shorter atmospheric life than chlorofluorocarbons (CFCs). This study proposes methyl chloroform (CH3CCl3) as the significant anthropogenic source of perchlorate in the Canadian High Arctic between 1980 and 2000, with HCFC-141b (Cl2FC-CH3), a relatively short-lived CFC probably responsible for a slower decrease in perchlorate deposition after the late 1990s. The presence of aerosols in the stratosphere appears to suppress perchlorate production after 1974. As both methyl chloroform and HCFC-141b had no new significant emissions after 2003, deposition of perchlorate in High Arctic is expected to remain at pre-1980 levels.
All of the elements form chemical species that have different oxidation states. Oxidation is the removal of electrons whereas reduction is the addition of electrons to a chemical species. The elements exist on the earth's surface based on their interactions with water, O2, and reductants such as H2S. When thermodynamically favorable electron transfer occurs between reactants, a potential is generated. Electron transfer reactions are termed redox reactions, which can be broken into two separate half-reactions and are readily described by thermodynamics. Most redox reactions involve only one or two electron transfers, and many involve hydrogen ion transfer. Thus, the potential for a half-reaction can vary with pH. Oxygen atom transfer reactions are formally two-electron transfer reactions. In this chapter, the thermodynamic basis for redox reactions and how to predict which chemical species of the elements exists on earth are presented. Example reactions are given in this and subsequent chapters.
It is only realised since about 2000 that perchlorate is a naturally occurring anion outside the Atacama desert in Chile (see e.g. Dasgupta et al. 2005; Parker et al. 2008). Interestingly this knowledge developed in the same period when the first methods were developed to analyse the stable chlorine isotope compositions of perchlorates (Ader et al. 2001; Sturchio et al. 2003). The analytical methods to analyse the chlorine isotope compositions were quickly followed by methods to analyse the oxygen isotope composition of perchlorates as well (Bao and Gu 2004; Böhlke et al. 2005).
Normal saline is a common biological solution which provides much better living environment for Staphylococcus aureus than deionized water, but the plasma-activated normal saline is found to have a stronger bactericidal effect than the plasma-activated deionized water. A model is developed for the explanation, from which various kinds of reactive chlorine/oxy-chlorine species (RCS), such as HClO, are found to be generated in the plasma-activated normal saline. The production pathways of RCS are elucidated, in which O3 plays as an important intermediate species. Compared to the plasma-activated deionized water, the concentrations of reactive oxygen/nitrogen species are lower, but the bactericidal effect is higher, implying that the RCS play a crucial role for the sterilization.
Perchlorate contamination is a serious problem because of its potential toxicity and health effects, adverse impacts on ecosystems, and possible indirect exposure pathways to humans. Therefore, it is urgent to reduce the perchlorate uptake by crops and speed up perchlorate degradation in the agro-ecosystem. A pot experiment was conducted to determine the effects of perchlorate on growth and chlorophyll content of two rice variety seedlings in sterilized and non-sterilized soils, and its accumulation in the rice plant. The distribution, migration and transformation of perchlorate in the soil-rice system were also investigated. The results showed that soil sterilization resulted in the promotion of rice plant height, root length, biomass and chlorophyll content when treated without perchlorate, whereas soil sterilization inhibited the growth of the two rice varieties significantly when treated with perchlorate. At the end of the pot experiment, perchlorate concentrations in roots, stems and leaves of two rice varieties planted in the sterilized soil were significantly less than those in the non-sterilized soil at low perchlorate concentration (0.1 mg/L). In non-sterilized soil, 69.70% and 88.55% of perchlorate were absorbed by the two rice varieties respectively, while in sterilized soil the levels were 21.55% and 13.98%. However, perchlorate concentrations in each organ of the two rice varieties in sterilized soil were significantly higher than those in non-sterilized soil with high perchlorate level (50.0 mg/L). The content of perchlorate in the two varieties of rice leaves in sterilized soil were 3.67 and 5.88 times as those in non-sterilized soil. This indicated that soil sterilization could slow down the accumulation of perchlorate in rice plants at low perchlorate levels, whereas it could speed up the accumulation of perchlorate in rice at high levels. The higher the treatment concentration of perchlorate, the higher the amount of perchlorate accumulation in the plant. Perchlorate amounts accumulated in the leaves were much higher than that in roots and stems. Microorganisms in soil greatly influenced the absorption of perchlorate by the two rice varieties tested. Compare with the initial concentration, the decrease of perchlorate content in non-sterilized soil was more than that in the sterilized soil. This indicated that perchlorate is not expected to remain in non-sterilized soil at significant concentrations. Both soil sterilization and high perchlorate treatment significantly reduced activities of soil urease and catalase. Thus, microorganisms play important roles in the bioremediation of perchlorate. ©, 2014, Editorial department of Molecular Catalysis. All right reserved.
Perchlorate (ClO 4-) as an emerging trace pollutant, has caused a great concern about its environmental pollution problems. The natural origin of ClO 4- as well as its formation mechanisms is a new research focus. In order to establish new environmental quality standards and safety concentration limits of ClO 4-, it is quite important to recognize its natural origins, background concentrations, transport and fate in various environmental media, but few researches were reported in China. In this paper, the background concentration levels of ClO 4- in tropospheric and stratospheric aerosol, atmospheric wet deposition (rain and snow), groundwater, seawater, soil and minerals are summarized. The data for CO 4- concentrations in the aerosol were very limited, such as 0.5-5 ppt in the stratospheric aerosol, < 1.8 ng/m 3 (Japan) and ~5.0 ng/m 3 (China) in the tropospheric aerosol. The ClO 4- concentrations in rain were ND-24 400 ng/L for more than 1 600 samples, and 1-18 ng/L in Arctic snow. The ClO 4- concentrations in groundwater were widely investigated in USA, and recently, some data were reported for China, Germany and India, which were mainly pooled in 10 -1-10 3 μg/L for more than 2 100 samples. The reported ClO 4- concentrations in sea water were 0.16-6.11 μg/L. As a dominant natural origin, the atmospheric reaction mechanisms (i. e., ozone oxidations, photochemical reactions, and lightning effects) and precursors of ClO 4- are highlighted. It is believed that the species of ClO 2-/ClO 2- is a critical precursor for the formation of natural ClO 4- at the atmosphere. The transport, fate, and biogeochemical cycling of natural ClO 4- in the environments are described in details. The isotope tracer approaches for identification of natural source of ClO 4- are briefly introduced. The research trends and currently existing problems are prospected.
Understanding the role of biology in planetary evolution remains an outstanding challenge to geobiologists. Progress towards unraveling this puzzle for Earth is hindered by the scarcity of well-preserved rocks from the Archean (4.0 to 2.5 Gyr ago) and Proterozoic (2.5 to 0.5 Gyr ago) Eons. In addition, the microscopic life that dominated Earth's biota for most of its history left a poor fossil record, consisting primarily of lithified microbial mats, rare microbial body fossils, and membrane-derived hydrocarbon molecules that are still challenging to interpret. However, it is clear from the sulfur isotope record and other geochemical proxies that the production of oxygen or oxidizing power radically changed the Earth's surface and atmosphere during the Proterozoic Eon, pushing it away from the more reducing conditions prevalent during the Archean. In addition to ancient rocks, our reconstruction of Earth's redox evolution is informed by our knowledge of biogeochemical cycles catalyzed by extant biota. The emergence of oxygenic photosynthesis in ancient Cyanobacteria represents one of the most impressive microbial innovations in Earth's history, and oxygenic photosynthesis is the largest source of O2 in the atmosphere today. Thus the study of microbial metabolisms and evolution provides an important link between extant biota and the clues from the geologic record. Here, we consider the physiology of Cyanobacteria (the only microorganisms capable of oxygenic photosynthesis), their co-occurrence with anoxygenic phototrophs in a variety of environments and their persistence in low oxygen environments, including in water columns as well as mats, throughout much of Earth's history. We examine insights gained from both the rock record and Cyanobacteria presently living in early Earth analog ecosystems and synthesize current knowledge of these ancient microbial mediators in planetary redox evolution. Our analysis supports the hypothesis that anoxygenic photosynthesis, including the activity of metabolically versatile cyanobacteria, played an important role in delaying the oxygenation of Earth's surface ocean during the Proterozoic Eon.
In our paper we present the results of our research, which was carried out by means of semiconductor sensor techniques (SCS), which allowed evaluating heterogeneous death-rate of ozone (γ) Teflon surface. When ozone concentration is near to Ambient Air Standard value, γ is assessed to be equal to 6,57*10-7. High technique response provide possibility to determine ozone contents in the air media and the percentage of ozone, decomposed on the communication surfaces and on the surfaces of installation in the low concentration range (1–100 ppb).
Simultaneous observations of stratospheric organic and inorganic chlorine were made in September 1993 out of Fort Sumner, New Mexico, using JPL balloon-borne MkIV interferometer. Between 15 and 20 km, a significant fraction (20-60%) of the inorganic chlorine could not be accounted for by the sum of measured HCl, ClONO2, and HOCl. Laboratory measurements of the reaction of ClO radicals on sulfuric acid solutions have indicated that, along with HCl, small amounts of perchloric acid, HClO4, were formed. Very little is known about the fate of HClO4 in the stratosphere and we use a photochemical box model to determine the impact of this new species on the partitioning of inorganic chlorine in the stratosphere. Assuming that HClO4 is photochemically stable, it is shown that in the enhanced aerosol loading conditions resulting from Mt. Pinatubo's eruption, HClO4 could represent a significant reservoir of chlorine in the lower stratosphere, sequestering up to 0.2 ppbv (or 50%) of the total inorganic chlorine at 16 km. The occurrence of this new species could bring to closure the inorganic chlorine budget deficiency made apparent by recent ER-2 aircraft in situ measurements of HCl.
The quantum yield, Φ1, in the primary process ClO3-(+hv) → ClO- + O2 (1) and the sum of the quantum yields Φ2 + Φ3 in the primary processes ClO3- (+hv) → ClO2 + O- (2) and ClO3- → ClO2- + O(3P) (3) were measured in the steady-state photolysis of aqueous ClO3- solutions at 214 and 229 nm. The ratio of the yields of ClO- and ClO3- in the reactions ClO2 → ClO- + O2 and ClO2 + O- → ClO3- (4) was determined by γ-radiolysis of aqueous solutions of ClO2 at varying pH. The finding that the ratio between the yields of ClO- and ClO3- in reactions 4 equals the ratio between Φ1 and the quantum yield, Φ0 = 1 - Φ1 - Φ2 - Φ3, for ClO3- returning to the ground state is taken as evidence that process 1 results from a cage-back reaction. This result combined with recent studies of the radiolysis of KClO3 crystals suggest that the primary processes in the photolysis of aqueous ClO3- originate in a common process by which O- is expelled from ClO3- upon photoexcitation. The expelled O- may escape the solvent cage containing ClO2 (process 2), or react in a cage-back reaction (process 0 and 1). During the expulsion of O- the photoproducts may convert to ClO2- and G(3P) (process 3).
Observations of Antarctic chlorine dioxide abundances in the austral
autumn and winter of 1991 (when aerosols concentrations were at
background levels) and 1992 (greatly enhanced aerosol concentrations)
are presented. It is found that in 1992, unlike 1991, chlorine dioxide
levels increased dramatically in the autumn when polar stratospheric
clouds were extremely unlikely to have been present. Model results
suggest that this was mainly caused by the direct activation of chlorine
nitrate on the aerosol surfaces. The effect of the Pinatubo aerosols
probably contributed to the unprecedented depth and areal extent of
Antarctic ozone depletion in 1992.
The absorption cross-sections of Cl2O6 and Cl2O4 have been obtained using a fast flow reactor with a diode array spectrometer (DAS) detection system. The absorption cross-sections at the wavelengths of maximum absorption (λmax) determined in this study are those of Cl2O6: (1.47±0.15)×10−17 cm2 molecule−1, at λmax=276 nm and T=298 K; and Cl2O4: (9.0±2.0)×10−19 cm2 molecule−1, at λmax=234 nm and T=298 K. Errors quoted are two standard deviations together with estimates of the systematic error. The shapes of the absorption spectra were obtained over the wavelength range 200–450 nm for Cl2O6 and 200–350 nm for Cl2O4, and were normalized to the absolute cross-sections obtained at λmax for each oxide, and are presented at 1 nm intervals. These data are discussed in relation to previous measurements.
Mass spectra of individual aerosol particles were acquired at altitudes up to 19 km during the WB-57 Aerosol Mission. Fluorine and chlorine were more abundant in tropospheric aerosols than in stratospheric aerosols. Chlorine in tropospheric aerosols was often associated with organics, soot, and mineral dust. Small amounts of perchlorate were observed in stratospheric sulfate aerosols, but aerosols do not represent a significant sink for total fluorine or chlorine in the lower stratosphere. Bromine was most common in aerosols just above the tropopause, where it may represent a significant fraction of inorganic Br. Both bromine and iodine were highly correlated with organics and probably were present in particles with Hg. The OH- and NO+ peak areas increased at temperatures below 195 K, providing evidence for the uptake of H2O and HNO3 by aerosols near a cold tropopause. There was evidence for uptake of chlorine but not the other halogens below 190 K.
Environmental context. Perchlorate, a well-known thyroid disruptor with both man-made and natural sources represents a major environmental problem in the United States but little information is available concerning the source of natural perchlorate. Previous research has demonstrated that perchlorate can be produced from exposure of some chlorine compounds to ultraviolet radiation, but no information was available how quickly or comparatively how much perchlorate was formed. The results of the present study can be used to evaluate the potential impact of ultraviolet processes on the overall occurrence of perchlorate in the environment.
Abstract. The present study provides new and important information on perchlorate (ClO4–) formation through ultraviolet (UV) photodissociation of unbuffered chlorite (ClO2–) solutions from the standpoint of kinetics under three different wavelength regimes having maximum emissions, λe,max, at 235.7, 300 and 350 nm. ClO4– production rates and yields were in general found to be inversely related, with higher yields and lower rates at higher wavelengths, and vice versa. A simple kinetic model for ClO4– production as a function of the ClO2– first-order decay constant and starting concentration was fitted to the experimental data, resulting in the calculation of a rate constant, k2, which is a function of light-source characteristics. Further, a conceptual scheme for ClO4– formation via photochemical reactions between oxychlorine species was proposed based on the experimental results and available literature. The present study is a further step towards understanding the formation of ClO4– from the photolysis of its precursors.
Ozone reacts with free aqueous chlorine when present as hypochlorite ion (OCl−) with a second order rate constant of 120 ± 15 M−1 s−1 at 20°C. About 77% of the chlorine reacts to produce Cl− and 23% is oxidized to ClO−3. No ClO−4 is formed. Conversion of chlorine to monochloramine reduces the ozone reaction rate to 26 ± 4 M−1 s−1, independent of pH, NH2Cl is transformed quantitatively to NO−3 and Cl− by O3. Rate data for other chloramines are also presented. The direct reaction of ozone with chlorine accounts for a significant amount of the chlorine and ozone demand found when the two oxidants are used in combination under water works conditions.
A basic reaction scheme for the integral process of chlorine dioxide (OClO) photolysis at 366nm in N2-saturated aqueous solution is proposed. The mechanism is supported by the initial quantum yield Φ°366nm determined experimentally from OClO decay rates measured by electron spin resonance (ESR), chemical analysis of the stable products in solution and numerical simulation of the OClO profiles. In the concentration range 0.5mM≤[OClO]≤20mM, Φ°366nm=0.52 with a 95% confidence interval of 0.50–0.55. Product concentrations determined after complete photobleaching were proportional to OClO initial concentration: [H+]=0.856 [OClO]0; [HClO]=(0.141±0.010) [OClO]0; [ClO3−]=(0.551±0.014) [OClO]0 and [Cl−]=(0.251±0.015) [OClO]0. In the range of homogeneous light absorption, i.e. [OClO]0≤1.5mM, OClO profiles and concentrations of the stable products in solution are well reproduced from numerical integration of the proposed mechanism. The reaction scheme requires the participation of dichlorine pentoxide (Cl2O5), which till now remains no isolated. However, reactions involving formation and hydrolysis of Cl2O5 are critical to reproduce the experimental profiles and explain the identity of the final products.
Electron transfer reactions of sulfate radical anion (SO
4
-
) and nitrate radical (NO
3
) with chlorate ion (ClO
3
-
) have been studied by laser photolysis. Reaction (1) leads to the formation of chlorine trioxide radical (ClO
3
) which has an absorption peak at 330 nm. Simulation work gave estimated results including: the forward and reverse rate constants of reaction (1), [k
f
=(4.0±0.5)×10
6
dm
3
mol
-1
s
-1
, k
r
=(5±5)×10
5
dm
3
mol
-1
s
-1
at ionic strength I=0], the second-order decay rate constant of ClO
3
[2k=(9.0±1.6)×10
8
dm
3
mol
-1
s
-1
], and its molar absorption coefficient [ε=(1500±250) dm
3
mol
-1
cm
-1
at 330 nm]. Reaction (2) was also observed and the forward and reverse rate constants were determined to be k
f
=(9.0±1.2)×10
3
dm
3
mol
-1
s
-1
and k
r
=(8.3±1.0)×10
2
dm
3
mol
-1
s
-1
. The equilibrium constant K of reaction (2) was determined to be 42±6, from the observed absorbance of the radicals at equilibrium. The reduction potential of ClO
3
, E
0
(ClO
3
/ClO
3
-
) was deduced to be 2.35±0.05 V vs. NHE when E
0
(NO
3
/NO
3
-
) is taken as 2.45±0.05 V vs. NHE.
The rate constants of the following reactions were determined by pulse radiolysis and stopped-flow experiments: ClO2- + O3 ⇄ ClO2 + O3- (kf = (4 ± 1) × 106 dm3 mol-1 s-1, kr = (1.8 ± 0.2) × 105 dm3 mol-1 s-1); ClO2 + OH → ClO3- + H+ (k = (4.0 ± 0.4) × 109 dm3 mol-1 s-1); ClO2 + O- → ClO3- (k = (2.7 ± 0.4) × 109 dm3 mol-1 s-1); and O3 + ClO2 → ClO3 + O2 (k = (1.05 ± 0.10) × 103 dm3 mol-1 s-1), where kf is the forward rate of reaction and kr is the reverse rate of reaction. The standard Gibbs energy of formation of OH in aqueous solution ΔfG°ao(OH) and the corresponding standard oxidation potential E°ao(OH/OH-) were determined by means of kf and kr, the equilibrium constant of O3- ⇄ O2 + O-, the pK of the hydroxyl radical, ΔfG°ao of O3, O2, and OH- in aqueous solution, and E°ao(ClO2/ClO2-) = 0.934 V determined in the present work. ΔfG°ao(OH) = 26.8 ± 1 kJ mol-1 and E°ao(OH/OH-) = 1.91 ± 0.01 V are obtained.
A pulse radiolysis study on concentrated aqueous chlorate solution was carried out. In the radiolysis of the chlorate system, ClO2 and ClO3 radicals are produced as a result of direct action of radiation on chlorate ion with G values of 1.0 and 1.5, respectively, whereas the slow formation process of ClO3 radicals is not observed. The absorption peak Of ClO3 radicals is around 330 +/- 10 nm and the absorption coefficient is evaluated as 4700 M-1 cm-1. The rate constants of some reactions of ClO3 radical with additives were determined.
The molar absorptivities of aqueous ozone solutions are reported for the wavelength ranges 190-300 nm and 350-900 nm. At the maxima of these bands, ε260(O3) = 3292 ± 70 M-1 cm-1 and ε590(O3) = 5.1 ± 0.1 M-1 cm-1. The analyses for ozone were carried out by absorbance measurements of the gas at 253.7 nm and by oxidation of ferrous sulfate in sulfuric acid solution followed by back-titration of excess ferrous ion with potassium permanganate. Spectrophotometric analysis of ferric ion was also used at low ozone concentrations. A stolchiometric ratio, Fe3+/O3, of 1.996 ± 0.036 was found. The visible spectrum of aqueous O3 is compared with that of ozone gas.
The IR spectrum of matrix-isqlated dichlorine hexaoxide shows that there are two inequivalent chlorine atoms in the molecule and that it is best described as the mixed anhydride of chloric and perchloric acids. Of 18 fundamental vibrations, 16 were observed and many of them were assigned. O3ClOClO2 exhibits a broad UV absorption at 268 nm (εmax = 3000 dm3 mol-1 cm-1) in the gas phase. It is decomposed on photolysis in an Ar matrix to ClOClO3 and O2. The kinetics of formation and decomposition of O3ClOClO2 in the gas phase were also investigated. The rate of formation depends strongly on the concentration of ClO2 and O3. Cl2O6 does not dissociate into ClO3 radicals, and the primary stable decomposition products are ClO2, ClOClO3, and O2.
Second-order rate constants for reactions of ozone with 40 inorganic aqueous solutes are reported. Included are compounds of sulfur (e.g. H2S, H2SO3, HOCH2SO3H), chlorine (e.g. Cl−, HOCl, NH2Cl, HClO2, ClO2), bromine (e.g. Br−, HOBr), nitrogen (e.g. NH3, NH2OH, N2O, HNO2) and oxygen (e.g. H2O2), as well as free radicals (e.g. O2−, OH•). Most of these compounds exhibit an increase in rate constant with increasing pH corresponding to their degree of dissociation. Rate constants are based on ozone consumption rates measured by conventional batch-type or continuous-flow methods (10−3-10+6 M−1 s−1 range) and determinations of stoichiometric factors. Also listed are data determined by pulse-irradiation techniques using kinetic spectroscopy (1010 M−1 s−1 range). Additional literature data are reviewed for completeness. Results are discussed with respect to water treatment and environmental processes.
The chlorate ion is one of the contaminants being considered for regulation in drinking water under the disinfection by-product rule. In addition to its presence in water as a result of chlorine dioxide use, chlorate may be formed during intermediate ozonation if residual chlorine is present. The majority of chlorate forms through a free radical pathway in natural source waters as opposed to by both molecular ozone and free radical pathways in low-DOC waters. The monitoring of OH radicals using p-chlorobenzoic acid indicated that the formation of chlorate is proportional to OH radical generation. The increase in pH favored chlorate formation and the presence of alkalinity enhanced chlorate formation due to secondary reactions between carbonate radicals and chlorine species. The addition of ammonia and peroxide before ozonation reduced chlorate formation whereas the simultaneous addition of peroxide during ozonation enhanced chlorate formation.
Five minimum energy structures have been identified for dichlorine hexoxide and ab initio calculations have been performed on these isomers at the 6–31G∗ and MP2/6–31G∗ levels. Among the five structures, the oxygen-bridged structure and a symmetrical dimer containing a ClCl bond were found to be stable. Normal mode analysis has been carried out on the stable conformers. The relative strength of the O3ClO and OClO2 bonds of the oxygen-bridged structure is discussed on the basis of their vibrational frequencies. In addition, the paper focuses attention on the great importance of the reaction 2OClO + 2O3 → Cl2O6 + 2O2. The implications of these results to the chemistry of stratospheric ozone depletion are delineated.
Isotopic analysis of nitrate and sulfate minerals from the nitrate ore fields of the Atacama Desert in northern Chile has shown anomalous 17O enrichments in both minerals. Δ17O values of 14–21 ‰ in nitrate and 0.4 to 4 ‰ in sulfate are the most positive found in terrestrial minerals to date. Modeling of atmospheric processes indicates that the Δ17O signatures are the result of photochemical reactions in the troposphere and stratosphere. We conclude that the bulk of the nitrate, sulfate and other soluble salts in some parts of the Atacama Desert must be the result of atmospheric deposition of particles produced by gas to particle conversion, with minor but varying amounts from sea spray and local terrestrial sources. Flux calculations indicate that the major salt deposits could have accumulated from atmospheric deposition in a period of 200,000 to 2.0 M years during hyper-arid conditions similar to those currently found in the Atacama Desert. Correlations between Δ17O and δ18O in nitrate salts from the Atacama Desert and Mojave Desert, California, indicate varying fractions of microbial and photochemical end-member sources. The photochemical nitrate isotope signature is well preserved in the driest surficial environments that are almost lifeless, whereas the microbial nitrate isotope signature becomes dominant rapidly with increasing moisture, biologic activity, and nitrogen cycling. These isotopic signatures have important implications for paleoclimate, astrobiology, and N cycling studies.
The possibility that chlorine may deplete stratospheric chlorine has received considerable attention recently. The only termination steps considered up to now involve HCl formation by chlorine atom attack on hydrogen-bearing molecules. We propose that an important removal mechanism for chlorine in the stratosphere may be the formation of HClO4 via the sequence of steps Cl + O2 + O3 → ClO3 + O2 ClO3 + OH → HClO4. In addition to being produced as often as HCl, HClO4 may be more stable to radical attack and thus a more efficient sink than HCl for stratospheric chlorine.
Natural perchlorate is believed to be of atmospheric origin, yet no systematic study has been conducted to evaluate perchlorate deposition rate and possible seasonal or spatial variations. This study evaluated perchlorate concentrations in weekly composite wet deposition samples acquired through the National Atmospheric Deposition Program from 26 sites across the continental United States, Alaska, and Puerto Rico for a 1-3 year period. Perchlorate concentrations varied from <5 ng/L to a high of 102 ng/L with a mean of 14.1 +/- 13.5 ng/L for the 1578 total samples. The annual perchlorate flux by site ranged from a low of 12.5 (TX) to 157 mg/ha-year (NE) and averaged 65 +/- 30 mg/ha-year for all sites. Perchlorate concentrations and flux in wet deposition were generally highest in May-August declining to lows in December-February. Average annual perchlorate flux was correlated (r > 0.5; p < 0.001) with Ca2+, K+, NH4+, NO3(-), Cl(-), and SO4(-2). Wet deposition rate of ClO4(-) in the conterminous United States (excluding Alaska, Hawaii, and Puerto Rico) while diffuse, represents a potential annual net mass flux of 51,000 kg, a value comparable to the estimated annual environmental releases from other known ClO4(-) sources.
Overwhelming evidence now exists that perchlorate is produced through natural processes and can be ubiquitously found at environmentally relevant concentrations in arid and semi-arid locations. A number of potential production mechanisms have been hypothesized and ClO4- production by ozone oxidation of surface bound Cl- was demonstrated. However, no information concerning the impact of concentration, final reaction products distribution, impact of reaction phase, or oxidation of important oxychlorine intermediates has been reported. Using IC-MS-MS analysis and replicate oxidation experiments, we show that exposing aqueous solutions or Cl- coated sand or glass surfaces to O3 (0.96%) generated ClO4- with molar yields of 0.007 and 0.01% for aqueous Cl- solutions and 0.025 and 0.42% for Cl- coated sand and glass, respectively. Aqueous solutions of Cl- produced less ClO4- than Cl- coated sand or glass as well as a higher ratio of ClO3- to ClO4-. Reduction of the initial Cl- mass resulted in substantially higher molar yields of ClO4- and ClO3-. In addition, alkaline absorbers that captured gaseous products contained substantial quantities of Cl-, ClO3-, and ClO4-. Solutions of possible oxychlorine intermediates (OCl- and ClO3-) exposed to O3 produced only scant amounts of ClO4- while a ClO2- solution exposed to O3 produced substantial molar yields of ClO4- (4% molar yield). Scanning electron microscopy coupled with energy energy-dispersive X-ray analysis demonstrated a significant loss of Cl- and an increase in oxygen on the Cl- coated silica sand exposed to O3. While the experimental conditions are not reflective of natural conditions this work clearly demonstrates the relative potential of Cl- precursors in perchlorate production and the likely importance of dry aerosol oxidation over solution phase reactions. It also suggests that ClO2- may be a key intermediate while ClO3- and OCl- are unlikely to play a significant role.
The rate of oxidation of ClO(2)(-) by HOBr is first-order in each reactant and is general-acid-assisted in the presence of phosphate or carbonate buffers. The products are ClO(2) and ClO(3)(-), where the relative yield depends on the concentration ratio of ClO(2)(-)/OH(-). The kinetic dependence indicates the presence of a steady-state intermediate, HOBrOClO(-) (or HOBrClO(2)(-)), that undergoes general-acid-assisted reactions to generate a metastable intermediate, BrOClO (or BrClO(2)). This intermediate reacts very rapidly by two competing pathways: in one path ClO(2)(-) reacts to form 2ClO(2) and Br(-), and in the other path OH(-) (or H(2)O) reacts to form ClO(3)(-) and Br(-). Competition between these pathways determines the yield of ClO(2) but does not affect the rate of loss of HOBr. The reactions are followed by the formation of ClO(2) in the presence of excess ClO(2)(-). The rate expression for the loss of HOBr is k(1)[ClO(2)(-)][HOBr] summation operator(k(HA)[HA])/(k(-)(1) + summation operator(k(HA)[HA])), where k(1) (for the formation of the intermediate) is 97 M(-)(1) s(-)(1) and k(HA)/k(-)(1) (M(-)(1)) values, which depend on the acid (HA) strength, are 3.1 x 10(5) for H(3)O(+), 8.3 for H(2)PO(4)(-), and 0.064 for HCO(3)(-) (25.0 degrees C, &mgr; = 1.0 M). Reactions between HOBr and ClO(2)(-) are much faster than those between HOCl and ClO(2)(-).
Ozone reactions with XO(2)(-) (X = Cl or Br) are studied by stopped-flow spectroscopy under pseudo-first-order conditions with excess XO(2)(-). The O(3)/XO(2)(-) reactions are first-order in [O(3)] and [XO(2)(-)], with rate constants k(1)(Cl) = 8.2(4) x 10(6) M(-1) s(-1) and k(1)(Br) = 8.9(3) x 10(4) M(-1) s(-1) at 25.0 degrees C and mu = 1.0 M. The proposed rate-determining step is an electron transfer from XO(2)(-) to O(3) to form XO(2) and O(3)(-). Subsequent rapid reactions of O(3)(-) with general acids produce O(2) and OH. The OH radical reacts rapidly with XO(2)(-) to form a second XO(2) and OH(-). In the O(3)/ClO(2)(-) reaction, ClO(2) and ClO(3)(-) are the final products due to competition between the OH/ClO(2)(-) reaction to form ClO(2) and the OH/ClO(2) reaction to form ClO(3)(-). Unlike ClO(2), BrO(2) is not a stable product due to its rapid disproportionation to form BrO(2)(-) and BrO(3)(-). However, kinetic spectra show that small but observable concentrations of BrO(2) form within the dead time of the stopped-flow instrument. Bromine dioxide is a transitory intermediate, and its observed rate of decay is equal to half the rate of the O(3)/BrO(2)(-) reaction. Ion chromatographic analysis shows that O(3) and BrO(2)(-) react in a 1/1 ratio to form BrO(3)(-) as the final product. Variation of k(1)(X) values with temperature gives Delta H(++)(Cl) = 29(2) kJ mol(-1), DeltaS(++)(Cl) = -14.6(7) J mol(-1) K(-1), Delta H(++)(Br) = 54.9(8) kJ mol(-1), and Delta S(++)(Br) = 34(3) J mol(-1) K(-1). The positive Delta S(++)(Br) value is attributed to the loss of coordinated H(2)O from BrO(2)(-) upon formation of an [O(3)BrO(2)(-)](++) activated complex.
Perchlorate is known to be a minor component of the hyperarid Atacama Desert salts, and its origin has long been a subject of speculation. Here we report the first measurement of the triple-oxygen isotope ratios (18O/16O and 17O/16O) for both man-made perchlorate from commercial sources and natural perchlorate extracted from Atacama soils. We found that the delta 18O values (i.e., normalized 18O/ 16O ratios) of man-made perchlorate were at -18.4+/-1.2%, whereas natural perchlorate has a variable delta 18O value, ranging from -4.5% to -24.8%. The delta 18O and delta 17O values followed the bulk Earth's oxygen isotope fractionation line for man-made perchlorate, but all Atacama perchlorates deviated from this line, with a distinctly large and positive 170 anomaly ranging from +4.2% to +9.6%. These findings provide a tool for the identification and forensics of perchlorate contamination in the environment. Additionally, they confirm an early speculation that the oxidation of volatile chlorine by 03 and the formation of HClO4 can be a sink (albeit a minor one) for atmospheric chlorine.
A simple and rapid method has been developed to simultaneously measure sub-microg/L quantities of the oxyhalide anions bromate, chlorate, iodate, and perchlorate in water samples. Water samples (10 mL) are passed through barium and hydronium cartridges to remove sulfate and carbonate, respectively. The method utilizes the direct injection of 10 microL volumes of water samples into a liquid chromatography-tandem triple-quadrupole mass spectrometry (LC-MS/MS) system. Ionization is accomplished using electrospray ionization in negative mode. The method detection limits were 0.021 microg/L for perchlorate, 0.045 microg/L for bromate, 0.070 microg/L for iodate, and 0.045 microg/L for chlorate anions in water. The LC-MS/MS method described here was compared to established EPA methods 300.1 and 317.1 for bromate analysis and EPA method 314.0 for perchlorate analysis. Samples collected from sites with known contamination were split and sent to certified laboratories utilizing EPA methods for bromate and perchlorate analysis. At concentrations above the reporting limits for EPA methods, the method described here was always within 20% of the established methods, and generally within 10%. Twenty-one commercially available bottled waters were analyzed for oxyhalides. The majority of bottled waters contained detectable levels of oxyhalides, with perchlorate < or = 0.74 microg/L, bromate < or = 76 microg/L, iodate < or = 25 microg/ L, and chlorate < or = 5.8 microg/L. Perchlorate, iodate, and chlorate were detectable in nearly all natural waters tested, while bromate was only detected in treated waters. Perchlorate was found in several rivers and reservoirs where itwas not found previously using EPA 314.0 (reporting limit of 4 microg/L). This method was also applied to common detergents used for cleaning laboratory glassware and equipmentto evaluate the potential for sample contamination. Only chlorate appeared as a major oxyhalide in the detergents evaluated, with concentrations up to 517 microg/g. Drinking water treatment plants were also evaluated using this method. Significant formations of chlorate and bromate are demonstrated from hypochlorite generation and ozonation. From the limited data set provided here, it appears that perchlorate is a ubiquitous contaminant of natural waters at trace levels.
Groundwater from remote parts of the Middle Rio Grande Basin in north-central New Mexico has perchlorate (ClO4-) concentrations of 0.12-1.8 micro/L. Because the water samples are mostly preanthropogenic in age (0-28000 years) and there are no industrial sources in the study area, a natural source of the ClO4- is likely. Most of the samples have Br-, Cl-, and SO4(2-) concentrations that are similar to those of modern bulk atmospheric deposition with evapotranspiration (ET) factors of about 7-40. Most of the ET values for Pleistocene recharge were nearly twice that for Holocene recharge. The N03-/Cl- and CIO-/Cl-ratios are more variable than those of Br-/Cl- or S04(2-)/Cl-. Samples thought to have recharged under the most arid conditions in the Holocene have relatively high N03-/Cl- ratios and low delta 15N values (+1 per mil (% per thousand)) similar to those of modern bulk atmospheric N deposition. The delta 18O values of the N03- (-4 to 0% per thousand) indicate that atmospheric N03- was not transmitted directly to the groundwater but may have been cycled in the soils before infiltrating. Samples with nearly atmospheric N03-/CI- ratios have relatively high Cl04- concentrations (1.0-1.8 ug/L) with a nearly constant Cl04-/CI- mole ratio of (1.4 +/- 0.1) x 10(-4), which would be consistent with an average Cl04-concentration of 0.093 0.005 ,ug/L in bulk atmospheric deposition during the late Holocene in north-central NM. Samples thought to have recharged under wetter conditions have higher delta 15N values (+3 to +8 % per thousando), lower NO3-/Cl- ratios, and lower ClO4-/Cl- ratios than the ones most likely to preserve an atmospheric signal. Processes in the soils that may have depleted atmospherically derived NO3-also may have depleted ClO4- to varying degrees prior to recharge. If these interpretations are correct, then ClO4- concentrations of atmospheric origin as high as 4 microg/L are possible in preanthropogenic groundwater in parts of the Southwest where ET approaches a factor of 40. Higher Cl04- concentrations in uncontaminated groundwater could occur in recharge beneath arid areas where ET is greater than 40, where long-term accumulations of atmospheric salts are leached suddenly from dry soils, or where other (nonatmospheric) natural sources of ClO4- exist.
Perchlorate (CLO4-) occurrence in groundwater has previously been linked to industrial releases and the historic use of Chilean nitrate fertilizers. However, recently a number of occurrences have been identified for which there is no obvious anthropogenic source. Groundwater from an area of 155,000 km2 in 56 counties in northwest Texas and eastern New Mexico is impacted bythe presence of ClO4-. Concentrations were generally low (<4 ppb), although some areas are impacted by concentrations up to 200 ppb. ClO4- distribution is not related to well type (public water system, domestic, agricultural, or water-table monitoring) or aquifer (Ogallala, Edward Trinity High Plains, Edwards Trinity Plateau, Seymour, or Cenozoic). Results from vertically nested wells strongly indicate a surface source. The source of ClO4- appears to most likely be atmospheric deposition. Evidence supporting this hypothesis primarily relates to the presence of ClO4- in tritium-free older water, the lack of relation between land use and concentration distribution, the inability of potential anthropogenic sources to account for the estimated mass of ClO4-, and the positive relationship between conserved anions (e.g., IO3-, Cl-, SO4(-2)) and ClO4-. The ClO4- distribution appears to be mainly related to evaporative concentration and unsaturated transport. This process has led to higher ClO4- and other ion concentrations in groundwater where the water table is relatively shallow, and in areas with lower saturated thickness. Irrigation may have accelerated this process in some areas by increasing the transport of accumulated salts and by increasing the number of evaporative cycles. Results from this study highlight the potential for ClO4- to impact groundwater in arid and semi-arid areas through long-term atmospheric deposition.
A substantial reservoir (up to 1 kg ha(-1)) of natural perchlorate is present in diverse unsaturated zones of the arid and semi-arid southwestern United States. The perchlorate co-occurs with meteoric chloride that has accumulated in these soils throughout the Holocene [0 to 10-15 ka (thousand years ago)] and possibly longer periods. Previously, natural perchlorate widely believed to be limited to the Atacama Desert, now appears widespread in steppe-to-desert ecoregions. The perchlorate reservoir becomes sufficiently large to affect groundwater when recharge from irrigation or climate change flushes accumulated salts from the unsaturated zone. This new source may help explain increasing reports of perchlorate in dry region agricultural products and should be considered when evaluating overall source contributions.
Evidence of atmospherically produced perchlorate is being accumulated, yet information regarding its formation process is largely unknown. For the first time, the present study demonstrates that perchlorate can be generated as an end-product of photochemical transformation reactions of chlorine precursors such as aqueous salt solutions of hypochlorite, chlorite, and chlorate upon exposure to ultraviolet (UV) radiation. For example, under exposure to UV light from photochemical reactor lamps at a peak wavelength of 253.7 nm for 7 days, the observed perchlorate concentrations were 5, 25, and 626 microg/L at initial chlorite concentrations of 100, 1000, and 10,000 mg/L, respectively. In addition, perchlorate was generated within 7 days from aqueous chlorite solutions at mid-latitude (33 degrees 59'N, 101 degrees 89'W) spring and summer solar radiation. Via UV radiation from the artificial lamps and sunlight, chlorite was converted to chloride (68%) and chlorate (32%) as end-products on the basis of molar percentage. However, perchlorate was not detected from aqueous chloride solutions at initial concentrations up to 10,000 mg/L under the experimental conditions. Relevant mechanistic pathways were proposed based on the fact that chlorine dioxide (as a primary intermediate) may play a significant role in phototransformation of the precursors leading to perchlorate.
Observations at Thule, Greenland, that made use of direct light from the moon on 2,3, 4,5, and 7 February 1988 revealed nighttime
chlorine dioxide (OClO) abundances that were less than those obtained in Antarctica by about a factor of 5, but that exceeded
model predictions based on homogeneous (gas-phase) photochemistry by about a factor of 10. The observed time scale for the
formation of OClO after sunset strongly supports the current understanding of the diurnal chemistry of OClO. These data suggest
that heterogeneous (surface) reactions due to polar stratospheric clouds can occur in the Arctic, providing a mechanism for
possible Arctic ozone depletion.
Naturalperchloratehasauniqueoxygenisotope signature
- H Bao
- B Gu
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Widespread presence of naturally occurringperchlorateinHighPlainsofTexasandNewMexico
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Rajagopalan, S.; Anderson, T. A.; Fahlquist, L.; Rainwater, K. A.; Ridley, M.; Jackson, A. W. Widespread presence of naturally occurringperchlorateinHighPlainsofTexasandNewMexico. Environ. Sci. Technol. 2006, 40, 3156–3162.
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