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Distribution of Polycyclic Aromatic Hydrocarbons in Soils of an Arid Urban Ecosystem
Abstract and Figures
Polycyclic aromatic hydrocarbons (PAHs) are widespread environmental pollutants produced by incomplete combustion sources
such as home heating, biomass burning, and vehicle emissions. PAH concentrations in soils are influenced by source inputs
and environmental factors that control loss processes and soil retention. Many studies have found higher concentrations of
these pollutants in soils within cities of temperate climates that have a centralized urban core. Less is known about the
factors regulating PAH abundance in warm, arid urban ecosystems with low population densities but high traffic volumes. The
relative importance of sources such as motor vehicle traffic load and aridland ecosystem characteristics, including temperature,
silt, and soil organic matter (SOM) were explored as factors regulating PAH concentrations in soils near highways across the
metropolitan area of Phoenix, AZ (USA). Highway traffic is high compared with other cities, with an average of 155,000 vehicles/day.
Soils contained low but variable amounts of SOM (median 2.8 ± 1.8% standard deviation). Across the city, median PAH concentrations
in soil were low relative to other cities, 523 ± 1,886μg/kg, ranging from 67 to 10,117μg/kg. Diagnostic ratio analyses confirmed
that the source of PAHs is predominantly fuel combustion (i.e., vehicle emissions) rather than petrogenic, biogenic, or other
combustion sources (coal, wood burning). However, in a multiple regression analysis including traffic characteristics and
soil properties, SOM content was the variable most strongly related to PAH concentrations. Our research suggests that dryland
soil characteristics play an important role in the retention of PAH compounds in soils of arid cities.
KeywordsSonoran desert–Soil organic matter–Urban ecosystem–PAH–Carbon deposition–Arid
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... In soil environments, microplastics can degrade through microbial action as microorganisms can utilize the carbon in plastic polymer chains for their growth (Mohanan et al., 2020;Huang et al., 2023). Owing to the low organic matter in dryland soils (Marusenko et al., 2011), soil microbes in these locations may resort to metabolize anthropogenic carbon sources such as microplastics. Studies have shown microplastics to have an acute toxic effect on soil organisms such as nematodes (Kim et al., 2020). ...
... Our study utilizes samples from the Ecological Survey of Central Arizona (ESCA) performed by the Central Arizona-Phoenix Long-Term Ecological Research (CAP-LTER), a large-scale field survey that is conducted in the CAP-LTER study area characterizing the urbanized, suburbanized, and agricultural areas of metropolitan Phoenix and the surrounding Sonoran Desert (Grimm and Redman, 2004). Previous studies have investigated various key ecological indicators and contaminants, including soot black carbon concentrations and isotopic compositions, PAHs and lead concentrations in soils (Marusenko et al., 2011;Zhuo et al., 2012;Hamilton and Hartnett, 2013). We leveraged the Ecological Survey of Central Arizona (ESCA) 200-point survey (2005 and 2015) to study spatial distributions and the temporal change of microplastic abundances. ...
... Topsoil samples (2 cm depth) were used for this study as this range could be expected to have the highest abundance of microplastics accumulated over time by direct input from terrestrial sources and atmospheric deposition. Top soil samples from the same study area were sampled and analyzed in a previous study for other environmental contaminants, such as PAHs (Marusenko et al., 2011). The soils analyzed in this study are desert soil samples, mainly from urban and suburban areas of metropolitan Phoenix and remote areas in the surrounding areas of the Sonoran Desert. ...
... Like pyrogenic anthracene and phenanthrene, the combustion of biomass and municipal waste could potentially be sources of fluoranthene and pyrene in the studied region. BaA/(BaA + Chr) ratio > 0.2 was found in the water, indicating that automobile exhaust sources could be a potential source of pollution (Marusenko et al., 2011). Based on the diagnostic ratios of PAHs, the primary sources of pollution in the studied region are pyrogenic, including fuel and biomass combustion. ...
The Shitalakshya River, vital to the Dhaka district, faces severe pollution challenges due to industrial discharges, urban runoff, and other anthropogenic activities. This study investigated the concentration of polycyclic aromatic hydrocarbons (PAHs) and heavy metals in the river water, utilizing GC–MS/MS and ICP-MS techniques. The results revealed a total PAH concentration ranging from 4.97 to 5.87 ng/mL, with 3-ring PAHs being the most prevalent. Heavy metals such as Fe, As, Ni, and Zn were found in significant concentrations, exceeding international standards for drinking water and aquatic life. The ecological risk assessment identified benzo(b)fluoranthene, benzo(k)fluoranthene, and indeno(1,2,3-cd)pyrene as the highest threats to aquatic organisms. Health risk assessments indicated substantial risks from dermal and ingestion exposures, particularly due to arsenic, highlighting potential long-term health implications for local residents. The study underscores the urgent need for comprehensive monitoring, pollution source identification, and stringent regulatory measures to mitigate these risks.
... Some studies also have been conducted on the sources and distributions of PAHs in atmosphere (Zheng and Fang, 2000), sediments (river, wetland and marine) (Budzinski et al., 1997;Gschwend et al., 1981) and marine (Richardson, 2003). However, it is di cult to identify the PAHs from raw coal and little is known about above ratio of PAHs from raw coal (Marusenko et al., 2011;Liu et al., 2007;Zhang et al., 2006). Therefrom, it is necessary to acquire the above ratio of PAHs in raw coal. ...
The concentrations of 16 Priority Pollutant polycyclic aromatic hydrocarbons (PAHs) in coals of varying rank were determined by high-performance liquid chromatography for obtaining the distribution of PAHs in raw coal with different metamorphic degree. The results indicate that the Σ 16 PAHs in coal ranged from 1416.28~131786.7 and 1896.85~133012.45 ng/g respectively with a the maximum yield when R 0 , max=1.47%. With the increase of coal rank, the toxicity of PAHs in raw coal increases and then decreases. The range of Flua / (Flua + Pyr), Ant / (Ant + Phe) and BaA / (BaA + Chr) is 0.237~0.340, 0.073~0.085, 0.064~0.178 and the total index of PAHs ranged from 3.17 to 3.74 in coals. Above diagnostic ratios are quite distinguished from petroleum origin, coal combustion and low-temperature combustion of coal gangue in previous work, which can be used to identify the sources of PAHs in complicated environment study.
... Unfortunately, we lack records documenting practices such as irrigation and the season when trees were planted and cannot draw conclusions about their possible effects. Highway environments can contain elevated levels of de-icing materials in cold-weather climates (Fay and Shi 2012), heavy metals in roadside soil (Werkenthin et al. 2014), and other air-borne (Kuttler and Strassburger 1999) and soil pollutants (Bryselbout et al. 2000;Marusenko et al. 2011), which all have the potential to affect tree growth. Exposure to sodium-based de-icing salts has been associated with diminished stem growth in roadside trees, though these impacts vary among species and roadside conditions (Blomqvist 1998). ...
Background: Highway rights-of-ways (ROWs, or verges) contain multiple stressors which can influence tree growth, including compacted soils, soils with little topsoil, poor drainage, air and soil pollutants, construction activities, and de-icing salts in cold climates. Yet highway ROWs often provide ample planting space for growing trees, which can contribute to the mitigation of negative environmental impacts associated with highways. Methods: For this study, we assessed the trunk diameter of 1,058 trees from 11-, 22-, and 31-year-old planting cohorts along a highway in the Chicago metropolitan region (Illinois, USA) to examine factors which could influence long-term growth. We analyzed the impact of location factors within the ROW (e.g., distance and elevation relative to highway, slope, and aspect) on trunk diameter at breast height (DBH), since these factors are relevant to the landscape design process. Using estimates from i-Tree, we compared carbon sequestration, carbon storage, runoff reduction, and air-pollution removal within and among the 3 cohorts. Results: Of the 6 site location characteristics we evaluated, no single characteristic consistently impacted DBH, though some characteristics were significant within a single cohort. DBH measurements of most species were smaller than model predictions based on existing urban tree models. Since all cohorts included large- and small-statured trees, and even within species DBH could be highly variable, the range in per-tree ecosystem services varied substantially within cohorts, especially the 31-year-old cohort. Conclusions: These findings highlight both the potential for and challenges of growing trees alongside highways.
... This leads to a decrease in the mineralizing and nitrifying activities of the microorganisms (White and McDonnell 1988). The main source of PAHs is fuel combustion (i.e., vehicle emissions), compared to petrogenic, biogenic, or other combustion sources (coal, wood combustion) (Marusenko et al. 2011). ...
At the moment, there is a large number of work aimed at studying the influence of urban environmental factors, both individually and in a complex way, on the nitrogen cycle in soils. Studying all the processes of the nitrogen cycle is a rather difficult job. That is why there is little research that covers all aspects of the nitrogen cycle in urban soils. In addition, there are works with conflicting results or that should be continued to obtain more accurate and reliable data. This chapter describes the results of studies examining the impact of urban environments on the nitrogen cycle. The first part of the chapter examines the specific conditions of the urban environment that affect the process of nitrogen transformation. The next section is devoted to a discussion on the processes involved in the nitrogen cycle, namely, nitrogen fixation, mineralization, nitrification, and denitrification, occurring in urban soils. It examines the influence of physical (compaction, waterlogging, sealing), chemical (pH, C/N ratio, fertilization, nitrogen deposition, heavy metals, and hydrocarbons), and biological effects on the mentioned processes. A conclusion is made on the consequences of disturbing the course of microbiological processes of nitrogen transformation in urban soils.
... In sediment and soil, the diagnostic ratios were similar and indicated a mix of sources. The diagnostic ratios used in this analysis were reported by Marusenko et al. (2011) andJiao et al. (2017) (see Table S10b, c). ...
Persistent organic pollutants (POPs) and polycyclic aromatic hydrocarbons (PAHs) were determined in abiotic samples from Concepción Bay in Central Chile. Samples were soxhlet extracted and injected in gas chromatography–mass spectrometry (GCMS). Polybrominated diphenyl ethers (PBDEs) showed the highest levels in air (3–1100 pg m⁻³), in water (2–64 pg L⁻¹), in sediment, and soil (1–78 ng g⁻¹ (dw)). PAHs were also high in the air (1–6 ng m⁻³), in water (1–7 ng L⁻¹), in sediment (90–300 ng g⁻¹ (dw)), and in soil (15–2300 ng g⁻¹ (dw)). The polychlorinated biphenyls (PCBs) and chlorinated pesticides were generally low and did not show clear trends along the water column, with exception of PAHs. New data are presented in this work to assess the health status of a relevant coastal area in central Chile.
... One possible explanation for this different relationship of the Σ16EPA-PAH with the Σ7OPAH concentrations might be that the local emissions contained a higher OPAH/PAH ratio than all other sites of our study. Alternatively, pronounced photochemical reactions in this semi-arid region might have produced more OPAHs than in the other study regions (Marquès et al., 2016(Marquès et al., , 2017Marusenko et al., 2011). On the other hand, the topsoil of the extremely PAH-contaminated chemical waste dump at Bratislava had a particularly low Σ7OPAH/Σ16EPA-PAH concentration ratio (Bandowe et al., 2011), likely because of unusually large PAH sources, which might have originated from PAH-rich industrial waste materials (e.g., industrially produced soot used for tires can contain high PAH concentrations). ...
Hazardous oxygenated polycyclic aromatic hydrocarbons (OPAHs) originate from combustion (primary sources) or postemission conversion of polycyclic aromatic hydrocarbons (PAHs) (secondary sources). We evaluated the global distribution of up to 15 OPAHs in 195 mineral topsoils from 33 study sites (covering 52° N–47° S, 71° W–118 °E) to identify indications of primary or secondary sources of OPAHs. The sums of the (frequently measured 7 and 15) OPAH concentrations correlated with those of the Σ16EPA‐PAHs. The relationship of the Σ16EPA‐PAH concentrations with the Σ7OPAH/Σ16EPA‐PAH concentration ratios (a measure of the variable OPAH sources) could be described by a power function with a negative exponent <1, leveling off at a Σ16EPA‐PAH concentration of approximately 400 ng g–1. We suggest that below this value, secondary sources contributed more to the OPAH burden in soil than above this value, where primary sources dominated the OPAH mixture. This was supported by a negative correlation of the Σ16EPA‐PAH concentrations with the contribution of the more readily biologically produced highly polar OPAHs (log octanol‐water partition coefficient <3) to the Σ7OPAH concentrations. We identified mean annual precipitation (Spearman ρ = .33, p < .001, n = 143) and clay concentrations (ρ = .55, p < .001, n = 33) as important drivers of the Σ7OPAH/Σ16EPA‐PAH concentration ratios. Our results indicate that at low PAH contamination levels, secondary sources contribute considerably and to a variable extent to total OPAH concentrations, whereas at Σ16EPA‐PAH contamination levels >400 ng g–1, there was a nearly constant Σ7OPAH/Σ16EPA‐PAH ratio (0.08 ± 0.005 [SE], n = 80) determined by their combustion sources.
In this study, 16 polycyclic aromatic hydrocarbons (PAHs) optimally controlled by the U.S. Environmental Protection Agency (EPA) were investigated. Three representative coal-fired power plants were selected as the research areas in Bijie, Guizhou Province, and 24 soil samples were collected totally from power plants at different depths and at different distances from the point pollution sources (plants). The physicochemical properties and microbial characteristics of the soil from the three power plants were also studied. The results showed that 16 PAHs were detected in all soils of the three power plants, with total concentrations ranging from 0.2 to 12.2 mg kg⁻¹, and that PAHs in the soils were mainly 2, 3 rings with percentages ranging from 42% to 82%. The proportions of low molecular weight (LMW) PAHs were higher near the contaminated plants. Moreover, since they were easily dispersed further away with atmospheric transfer, the proportions of lighter LMW PAHs were also higher far from the point source, while the proportions of heavier high molecular weight (HMW) PAHs were higher at some distance from the point source. In addition, the distribution patterns of PAHs in the soil at different depths were slightly different because the microbial activity in the surface soil at each sampling site was greater than that in the deeper soil, and the leaching behavior of each compound was different. Finally, based on the principal component analysis (PCA) method, coal combustion is not the only source of PAHs in soils from power plants, and vehicle emissions cannot be negligible.
Oases environments in oases to be sensitive to anthropogenic activity because of ecological fragility. Polycyclic aromatic hydrocarbon (PAH) pollution resulting from anthropogenic activity leads to ecological degradation in oases. To examine the impact of anthropogenic activity on the oasis ecological environment, the present study focused on the spatial distribution and source apportionment of soil PAHs and bacterial community responses in typical oases in Xinjiang, China. The results showed that the soil PAH level were higher in the city centres of Urumqi (9–6340 μg kg⁻¹), Aksu (8–957 μg kg⁻¹) and Korla (8–1103 μg kg⁻¹) and lower in the centres of Hotan city (11–268 μg kg⁻¹) and Qira county (7–163 μg kg⁻¹). Source apportionment suggested that gasoline emissions, diesel emissions, vehicle emissions, coal combustion, coke processing and biomass burning were the sources of soil PAHs. The integrated lifetime cancer risks of soil PAH exceeding the guideline safety values (10⁻⁶) recommended by United States Environmental Protection Agency. The ingestion and dermal exposure pathways caused the greatest health risk (contribution ≤82%). Additionally, in the soil with low PAH concentrations, the richness and evenness of the soil bacterial community were great, and the molecular ecological network (MEN) structure was complex. Among populations, Proteobacteria and Actinobacteria (relative abundance ≥17%) are the main dominant species in the bacterial communities and the keystone species in the MEN.
PAHs are mainly produced by combustion processes and consist of a number of toxic compounds. While the concentrations of individual PAHs in soil produced by natural processes (e.g., vegetation fires, volcanic exhalations) are estimated to be around 1—10 μg kg⁻¹, recently measured lowest concentrations are frequently 10 times higher. Organic horizons of forest soils and urban soils may even reach individual PAH concentrations of several 100 μg kg⁻¹. The PAH mixture in temperate soils is often dominated by benzofluoranthenes, chrysene, and fluoranthene. The few existing studies on tropical soils indicate that the PAH concentrations are relatively lower than in temperate soils for most compounds except for naphthalene, phenanthrene, and perylene suggesting the presence of unidentified PAH sources. PAHs accumulate in C-rich topsoils, in the stemfoot area, at aggregate surfaces, and in the fine-textured particle fractions, particularly the silt fraction. PAHs are mainly associated with soil organic matter (SOM) and soot-like C. Although the water-solubility of PAHs is low, they are encountered in the subsoil suggesting that they are transported in association with dissolved organic matter (DOM). The uptake of PAHs by plants is small. Most PAHs detected in plant tissue are from atmospheric deposition. However, earthworms bioaccumulate considerable amounts of PAHs in short periods. The reviewed work illustrates that there is a paucity of data on the global distribution of PAHs, particularly with respect to tropical and southern hemispheric regions. Reliable methods to characterize bioavailable PAH pools in soil still need to be developed.
Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous organic pollutants in urban environments. Incomplete combustion of petroleum and coal are the primary sources of elevated concentrations of urban PAHs. The purposes of the study were: 1) to determine and compare the concentration of PAHs in soils taken from two major US cities, New Orleans and Detroit; and 2) to examine the main sources of PAHs in urban soils by diagnostic PAH ratios. A total of 107 New Orleans soil samples were taken from 6 census tracts (n = 13–19 per census tract) and compared with 106 Detroit soil samples from 6 census tracts. Sampling sites included house foundations, open spaces, and soil bordering residential and busy streets. The average total PAH (sum of 17 PAH concentrations) of Detroit soils was 7,843 μ g/kg, compared to 5,100 μ g/kg for New Orleans soils. Several diagnostic PAH concentration ratios were calculated for source determination for Detroit and New Orleans, respectively: phenanthrene/anthracene ratios (2.97 and 5.36), benz(a)anthracene/chrysene ratios (0.99 and 0.85), benzo(b)fluoranthene/benzo(k)fluoranthene ratios (1.51 and 1.53), and benzo(a)pyrene/benzo(e)pyrene ratios (0.98 and 0.92). The ratios indicate that PAH concentrations are attributable to pyrolytic sources, mainly vehicle exhaust. Travel and gasoline consumption data in Detroit and New Orleans support these findings.
Tehran as the biggest city of Iran with a population of more than 10 millions has potentially high pollutant exposures of gas oil and gasoline combustion from vehicles that are commuting in the highways every day. The vehicle exhausts contain polycyclic aromatic hydrocarbons, which are produced by incomplete combustion and can be directly deposited in the environment. In the present study, the presence of polycyclic aromatic hydrocarbons contamination in the collected samples of a western highway in Tehran was investigated. The studied location was a busy highway in Tehran. High performance liquid chromatography equipped with florescence detector was used for determination of polycyclic aromatic hydrocarbons concentrations in the studied samples. Total concentration of the ten studied polycyclic aromatic hydrocarbons compounds ranged from 11107 to 24342 ng/g dry weight in the dust samples and increased from 164 to 2886 ng/g dry weight in the soil samples taken from 300 m and middle of the highway, respectively. Also the average of ∑ PAHs was 1759 ng/L in the water samples of pools in parks near the highway. The obtained results indicated that polycyclic aromatic hydrocarbons contamination levels were very high in the vicinity of the highway.
The fate of 14 polycyclic aromatic hydrocarbon (PAH) compounds was evaluated with regard to interphase transfer potential and mechanisms of treatment in soil under unsaturated conditions. Volatilization and abiotic and biotic fate of the PAHs were determined using two soils not previously exposed to these compounds. Volatilization accounted for approximately 30 and 20% loss of naphthalene and 1-methylnaphthalene, respectively; for the remaining compounds, volatilization was negligible. Abiotic reactions accounted for approximately 2 to 20% of the reduction in concentration in solvent extracts for two- and three-ring PAH compounds; no statistically significant reduction was observed in PAH compounds containing greater than three aromatic rings. Biotic mechanisms were quantified as first-order rate constants corrected for volatilization and abiotic mechanisms. Half-life values increased from approximately 2 to 60 to more than 300 d for two-, three- and four- and five-ring PAH compounds, respectively. In general, biological degradation rates were not significantly different between the two soils. Information concerning interphase transfer potential and mechanisms of treatment provides the basis for a rational approach to remediation of soil contaminated with PAH compounds.
The level of the environment pollution with polycyclic aromatic hydrocarbons is mainly in correlation with degree of the region industrialization and the traffic density. The aim of this study was to determine the effect of exhaust gases of gasoline and diesel motors on the polycyclic aromatic hydrocarbons (PAHs) accumulation in the soil, along the main road M-21. Soil samples were collected from seven localities, at two depths (0–20 and 20–40 cm). The method used for PAHs determination was gas chromatography—mass spectrometry (GC-MS). The obtained results showed that PAH concentrations, mainly originating from diesel motors, were lower than 1 mg/kg soil. Concentrations of phenanthrene, benzo(a)anthracene and benzo(b)fluoranthene were elevated at all chosen localities and at depths of 0–40 cm.
Amounts of polycyclic aromatic hydrocarbons (PAHs) and oxygenated polycyclic aromatic hydrocarbons (oxy-PAHs) in samples collected from the air, from the dust on a guardrail, and from the soils on a tunnel roadway at five sampling sites in a regular roadway tunnel were chemically analyzed in order to determine their sources. Among the 23 PAHs found in the air samples, pyrene was found in the highest concentration (43±7.2 ng/m3), followed by fluoranthene (26±4.3 ng/m3). Among 20 oxy-PAHs found in the air samples, anthraquinone was found in the greatest amount (56±3.9 ng/m3). The average concentration of the major PAHs found in the guardrail dust samples were 6.9±0.77 μg/g for pyrene, 5.5±0.76 μg/g for fluoranthene, and 2.6±0.30 μg/g for phenanthrene. The average concentration of the major oxy-PAHs found in the guardrail dust samples were 9.2±3.5 μg/g for anthraquinone and 1.4±0.50 μg/g for 2-methylanthraquinone. The average concentration of the major PAHs found in the soil samples were 1.1±0.31 μg/g for fluoranthene, 0.92±0.21 μg/g for pyrene, and 0.72±0.16 μg/g for phenanthrene. The average concentration of the major oxy-PAHs found in the soil samples were 1.2±0.88 μg/g for anthraquinone, 0.18±0.04 μg/g for 4-biphenylcarboxaldehyde, and 0.13±0.08 μg/g for 2-methylanthraquinone. The BeP ratios calculated from the results suggest that most PAHs found in the samples collected from the roadway tunnel were from automobile exhaust gases.
Gasoline- and diesel-powered vehicles are known to contribute appreciable amounts of inhalable fine particulate matter to the atmosphere in urban areas. Internal combustion engines burning gasoline and diesel fuel contribute more than 21% of the primary fine particulate organic carbon emitted to the Los Angeles atmosphere. In the present study, particulate (d[sub p] [le] 2 [mu]m) exhaust emissions from six noncatalyst automobiles, seven catalyst-equipped automobiles, and two heavy-duty diesel trucks are examined by gas chromatography/mass spectrometry. The purposes of this study are as follows: (a) to search for conservative marker compounds suitable for tracing the presence of vehicular particulate exhaust emissions in the urban atmosphere, (b) to compile quantitative source profiles, and (c) to study the contributions of fine organic particulate vehicular exhaust to the Los Angeles atmosphere. More than 100 organic compounds are quantified, including n-alkanes, n-alkanoic acids, benzoic acids, benzaldehydes, PAH, oxy-PAH, steranes, pentacyclic triterpanes, azanaphthalenes, and others. Although fossil fuel markers such as steranes and pentacyclic triterpanes can be emitted from other sources, it can be shown that their ambient concentrations measured in the Los Angeles atmosphere are attributable mainly to vehicular exhaust emissions. 102 refs., 9 figs., 6 tabs.
The bioavailability of persistent organic pollutants in soils depends on their sorption strength that may vary among different pools. We hypothesized that polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) had different soil organic C-water partition coefficients (Koc) among particle-size fractions. We determined the concentrations of 20 PAHs and 12 PCBs in coarse-sand, fine-sand, silt, and clay fractions of 11 urban topsoils (0-5 cm). The Koc values were determined using sequeutial extraction with methanol-water mixtures (35 and 65% methanol) at 60°C. The ∑20 PAHs concentrations ranged from 0.3 to 186 mg kg-1, the ∑12 PCBs concentrations from 1.2 to 158 μg kg-1. In most soils, the PAH concentrations decreased in the order, silt > clay ≥ fine sand > coarse sand, and those of the PCBs in the order, clay > silt ≥ fine sand > coarse sand. The distribution of PAHs among particle-size fractions was more heterogeneous than reported in the literature because the soils received PAH-contaminated wastes (ashes, slags, rubble) with varying texture. In all soils, the proportions of two- or three-ring PAHs decreased with decreasing particle size, indicating that the PAH mixture was increasingly altered. The Koc values of the PAHs were three to 10 times higher than those of the PCBs with similar octanol-water partition coefficients (Kow). The mean Koc values of all individual PAHs were highest in silt. For all individual PCBs, mean Koc values were highest in clay. The Koc values of PAHs and PCBs varied up to a factor of 100 among the studied soils and particle-size fractions. Particle-size fractions with highest PAH and PCB concentrations also showed highest Koc values indicating low bioavailability.
Among the controls on the fate of harzardous persistent organic pollutants (POPs) in the environment, soil organic matter (SOM) and climate play an outstanding role. Thus, it may be possible to predict POP concentrations at background sites from SUM properties and climatic elements. We therefore related polycyclic aromatic hydrocarbon (PAH) and polychorinated biphenyl (PCB) concentrations in 18 mollic epipedons under native grassland to SOM properties (lignin-derived phenols, polycarboxylic benzoic acids [PCBAs], aromaticity, and polarity of alkali-extractable SOM) and climatic elements. The sum of 20 PAH (∑20PAHs) concentrations ranged from 63 to 321 μg kg-1, and that of 14 PCB (∑14 PCBs) concentrations ranged from 7.9 to 93 μg kg-1, except at one contaminated site (3136 μg kg-1). On average, phenanthrene (PHEN, 38% of the ∑20PAHs concentrations) and naphthalene (NAPH, 28%) were the most abundant PAHs, congeners 28 (22% of the ∑14PCB concentrations) and 101 (17%) were the most abundant PCBs. Soil organic C (SOC) concentrations correlated with the ∑20PAHs concentrations; the C concentration in the sum of eight PCBAs, a marker for black C, correlated with the concentrations of higher molecular weight PAHs, except in soils with cyric temperature regime. The ∑14PCBs concentrations was independent of any soil property. The contribution of NAPH to the ∑20PAHs concentrations and that of the up to chlorinated PCBs to the ∑14PCBs concentrations decreased with tetra-increasing mean annual temperature (MAT). The percentages of PCB 101 increased with increasing MAT. However, the temperature effect was not strong. Mean annual precipitation (MAP) neither effected PAH nor PCB patterns. Our results indicate that the easily measured SOC concentrations may be used to predict PAIl concentrations in native grassland soils of the prairie. Inclining MAT improves the prediction of NAPH concentrations. The influence of MAT on PCB concentrations is obvious, but the correlation is too weak to be used for reliable predictions.
Astonishing as it may seem, one organism's waste is often ideal food for another. Many waste products generated by human activities are routinely degraded by microorganisms under controlled conditions during waste-water treatment. Toxic pollutants resulting from inadvertent releases, such as oil spills, are also consumed by bacteria, the simplest organisms on Earth. Biodegradation of toxic or particularly persistent compounds, however, remains problematic. What has escaped the attention of many is that bacteria exposed to pollutants can adapt to them by mutating or acquiring degradative genes. These bacteria can proliferate in the environment as a result of the selection pressures created by pollutants. The positive outcome of selection pressure is that harmful compounds may eventually be broken down completely through biodegradation. The downside is that biodegradation may require extremely long periods of time. Although the adaptation process has been shown to be reproducible, it remains very difficult to predict.