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Comparison of gadopentetic acid (Gd-DTPA) and bromide in a dual-tracer field experiment
Abstract
At a test site consisting of a storage pond and connected artificial aquifer, the long-time behaviour of gadopentetic acid (Gd-DTPA) was compared with the classic tracer bromide (Br-) in a 70-day dual-tracer experiment. The mixed tracer solution was injected into the oligotrophic pond, which is separated from the aquifer by an infiltration bank. The water drained from the aquifer was returned to the pond together with additional fresh groundwater, causing reduced concentrations of Gd-DTPA and Br- in the system. Transmetallation of Gd-DTPA by rare earth elements and yttrium was negligible but Cu2+ and Ni2+ might have played a role. Adsorption and/or biodegradation of Gd-DTPA were negligible. The decline of Gd-DTPA/Br ratios by 18% in the pond over 68 days was caused by reversible sorption of Br- in the aquifer, which caused variation of Br- background. Thus, Br- behaves less conservatively than Gd-DTPA in the aquifer. Comparison of both proves the suitability of Gd-chelates as tracers in hydrological studies. The advantage of Gd-DTPA as a tracer is that natural Gd3+ in water can continuously be monitored by analysing the suite of naturally occurring rare-earth elements. Thus, stable organic Gd-chelates are determinable with high precision at very low concentrations.
... A study of Möller et al. [201] reports that Gd complexes are stable and pass through wastewater systems almost unchanged, showing that it is neither adsorbed not co-precipitated, nor does it undergo ion exchange with organic or inorganic particulate sewage matter. Other studies report on the conservative behaviour of anthropogenic complexes of Gd [202]. Some authors as Telgmann et al. [203] report on the trans-metallation with endogenous ions of Fe 3+ , Zn 2+ , and Cu 2+ as being responsible for the release of toxic Gd 3+ ions. ...
The production of rare earth elements, REE, has significantly increased over the past years, in parallel with the latest advances in nanotechnologies and representing a new group of emerging contaminants. They find application in construction, transport, agriculture, electronics, catalysis, and biomedicine. Their extraordinary intrinsic characteristics are fundamental for overcoming current technological challenges. The accumulation of REE is consistent in near-shore waters being affected by runoff, wastewater discharge, and proximity to built-up areas. Bioavailability in water, sediments, and accumulation in marine biota as well their endocrine disruptor effect is mostly unknown. There is a significant gap of knowledge on the ecotoxicological behaviour of REE in marine areas. The existing investigations have been performed inside well-mixed estuarine systems, due to complex hydrodynamics and multiple sediment transport situations. This hampers the definition of regulatory thresholds for REE concentrations and emissions. The review summarizes the existing information on REE geochemistry and physicochemical conditions influencing dissolution, surface complexation reactions, and distribution at the continent–ocean interface, as well as their speciation, bioavailability, and detrimental effects on living organisms. Strategies for reducing REE usage and inputs are also discussed.
... Under natural conditions, Gd-CAs are highly stable and soluble (Bau et al. 2006;Möller and Dulski 2010;Birka et al. 2016;Beck et al. 2017), and differently from geogenic Gd (Gd geo ), Gd anth behaves conservatively (Verplanck et al. 2005;Kulaksiz and Bau 2007;Dulski et al. 2011). Gd anth is mainly associated with surface waters of highly populated urban areas with a well-developed health care system (high number of MRI facilities) and that receive water discharge from WWTPs (Lawrence et al. 2009;Birka et al. 2013;Song et al. 2017). ...
Anthropogenic gadolinium (Gdanth) is a frequent contaminant in surface water that receives wastewater treatment (WWT) effluents due to the high stability of Gd-based contrast agents (Gd-CAs) used in magnetic resonance imaging (MRI) exams and excreted by patients. This study describes the presence of Gdanth in surface water of a small drainage area (circa 4 km2), which does not receive WWT effluents. The unexpected Gdanth anomalies were attributed to raw sewage leaking from underground effluent removal pipes. The study area is within a university campus with a hospital that regularly runs MRI exams employing Gd-CAs. Besides Gd, the whole lanthanide (Ln) series was measured and except for Gd, all remaining Ln data were correlated, implicating that besides the natural Gd, a distinct Gd species contributes up to 95% to its whole content in the water samples. Besides surface water, samples of the local sewage and pluvial water networks were collected and analyzed. The ratio between measured and expected Gd values (Gd/Gd*) in surface water samples ranged between 1 and 46, the first corresponding to pristine locations and absence of Gd anomaly and the second nearby the sewage and pluvial water networks. The Gdanth anomalies presented transient values, probably associated with the application of the Gd-CAs to patients and their permanence in the hospital. Other proxies commonly associated to sewage discharge also presented transient values, not necessarily correlated Gdanth, because of the input of distinct anthropogenic sources in the study area.
... A first study on the stability of Gd-complex show that it pass through wastewater treatment plants almost unchanged showing that it is neither adsorbed, co-precipitated nor undergo ion exchange with organic or inorganic particulate sewage matter (Möller et al., 2003). Other studies about the stability of anthropogenic gadolinium showed that the anthropogenic gadolinium seemed to behave conservatively in aquatic environment (Verplanck et al., 2005;Kulaksiz and Bau, 2007;Dulski et al., 2011). Therefore, it may be an excellent tracer of wastewater contamination. ...
... Source: Reprinted with permission of [69]. 2005, Petelet-Giraud et al. in 2009, Lawrence and Bariel in 2010 and Dulski et al. in 2011[76][77][78][79]. ...
The development of analytical methods and strategies to determine gadolinium and its complexes in biological and environmental matrices is evaluated in this review. Gadolinium (Gd) chelates are employed as contrast agents for magnetic resonance imaging (MRI) since the 1980s. In general they were considered as safe and well-tolerated, when in 2006, the disease nephrogenic systemic fibrosis (NSF) was connected to the administration of MRI contrast agents based on Gd. Pathogenesis and etiology of NSF are yet unclear and called for the development of several analytical methods to obtain elucidation in this field. Determination of Gd complex stability in vitro and in vivo, as well as the quantification of Gd in body fluids like blood and urine was carried out. Separation of the Gd chelates was achieved with high performance liquid chromatography (HPLC) and capillary electrophoresis (CE). For detection, various methods were employed, including UV-vis absorbance and fluorescence spectroscopy, electrospray ionization mass spectrometry (ESI-MS) and inductively coupled plasma mass spectrometry (ICP-MS). A second challenge for analysts was the discovery of high concentrations of anthropogenic Gd in surface waters draining populated areas. The source could soon be determined to be the increasing administration of Gd complexes during MRI examinations. Identification and quantification of the contrast agents was carried out in various surface and groundwater samples to determine the behavior and fate of the Gd chelates in the environment. The improvement of limits of detection (LOD) and limits of quantification (LOQ) was and still is the goal of past and ongoing projects.
REE and Y (REY) distribution in the lowland Havel River passing the Federal State of Berlin, Germany, depends on contributions of point sources such pharmaceutical and high-tech industries, acid water from the open pit lignite mining, and medical application of very stable organic Gd chelates. Another omnipresent dispersed source of REY are water-soluble Ca-phosphates containing micro-amounts of Eu(II)-bearing barite as components of common agricultural fertilizers. After distribution in the field during the cold season (October through March) these Ca-phosphates dissolve and secondary phosphates and calcite precipitate both being enriched in light REE. Heavy REE are preferably exported by runoff together with part of the micro-contaminant barite leading to high Yb/Nd ratios in the Havel water and REY distribution patterns with only small Eu deficits. During the warm season (April through September) light REE together with phosphate are leached from secondary soil minerals by runoff. The micro-component barite is retained in vegetation-covered soil. Thus, REY patterns of Havel water show significant Eu deficits. The high Gd anomalies result from medical applications of Gd-chelates which after urination pass the sewage treatment plants. The seasonal variations of total Gd in the Havel River are artifacts based on seasonal locally varied discharge of effluents from sewage treatment plants. The natural Gd concentration of 8 pmol/l in the northern Havel is enhanced to 3300 pmol/l, when the Havel River leaves Berlin territory. The elimination of phosphate from Lake Tegel water affects the fractionation of REE but not the concentration of total Gd. Although enhanced in total phosphorus (TP), the REE concentrations in the water from the Spree River and the Teltow Canal are less than in the Havel water before their confluence. Only Yb and Lu do not decrease. The contributors of the Havel River are high in total organic carbon (TOC) and dissolved organic carbon (DOC) compared to the Havel water before their indicating that REY are preferentially sorbed by settling organic matter. Applying PHREEQC and assuming that only 10% of TP is present as ortho-phosphate yields that only carbonate complexes are essential.
We demonstrate the utility of nuclear medical imaging technologies and a readily available radiotracer, [99mTc]TcO4-, for the non-invasive monitoring of Fe(II) production in acetate-stimulated sediments from Old Rifle, CO, USA. Microcosms consisting of sediment in artificial groundwater media amended with acetate were probed by repeated injection of radiotracer over three weeks. Gamma camera imaging was used to non-invasively quantify the rate and extent of [99mTc]TcO4- partitioning from solution to sediment. Aqueous Fe(II) and sediment-associated Fe(II) were also measured and correlated with the observed tracer behavior. For each injection of tracer, curves of 99mTc concentration in solution vs. time were fitted to an analytic function that accounts for both the observed rate of sedimentation as well as the rate of 99mTc association with the sediment. The rate and extent of 99mTc association with the biostimulated sediment correlated well with the production of Fe(II) and a mechanism of [99mTc]TcO4- reduction via reaction with surface bound Fe(II) to form an immobile Tc(IV) species was inferred. After three weeks of bioreduction, a subset of microcosms was aerated in order to reoxidize the Fe(II) to Fe(III), which also destroyed the affinity of the [99mTc]TcO4- for the sediments. However, within 3 days post oxidation, the rate of Tc(VII) reduction was faster than immediately before oxidation implying a rapid return to more extensive bioreduction. Furthermore, aeration soon after a tracer injection showed that sediment-bound Tc(IV) is rapidly resolubilized to Tc(VII). In contrast to the 99mTcO4-, a second commercially available tracer, 99mTc-DTPA (diethylenetriaminepentaacetic acid), had minimal association with sediment in both controls and biostimulated sediments. These experiments show the promise of [99mTc]TcO4- and 99mTc-DTPA as non-invasive imaging probes for a redox sensitive radiotracer and a conservative flow tracer, respectively.
Distribution coefficients were obtained for yttrium and the rare earth elements (YREEs) in aqueous solutions containing freshly precipitated hydroxides of trivalent cations (Fe3, Al3+, Ga3+, and In3+). Observed patterns of logiKS-, where iKS = [MSi][M3+]-1[i] -1, [MSi] is the concentration of a sorbed YREE, [M3+] is the concentration of a free hydrated YREE ion, and [Si] is the concentration of a sorptive solid substrate (Fe(III), Al, Ga, In) - exhibited similarities to patterns of YREE solution complexation constants with hydroxide (OHβ 1) and fluoride (Fβ1), but also distinct differences. The logiKS pattern for YREE sorption on Al hydroxide precipitates is very similar to the pattern of YREE hydroxide stability constants (logOHβ1) in solution. Linear free-energy relationships between logiKS and logOHβ1 showed excellent correlation for YREE sorption on Al hydroxide precipitates, good correlation for YREE sorption on Ga or In hydroxide precipitates, yet poor correlation for YREE sorption on Fe(III) hydroxide precipitates. Whereas the correlation between logiKS and logFβ1 was generally poor, patterns of log (iKS/Fβ1) displayed substantially increased smoothness compared to patterns of logiKS. This indicates that the conspicuous sequence of inflections along the YREE series in the patterns of log iKS and logFβ1 is very similar, particularly for In and Fe(III) hydroxide precipitates. While the logiKS patterns obtained with Fe(III) hydroxide precipitates in this work are quite distinct from those obtained with Al, Ga, and In hydroxide precipitates, they are in good agreement with patterns of YREE sorption on ferric oxyhydroxide precipitates reported by others. Furthermore, our logiKS patterns for Fe(III) hydroxide precipitates bear a striking resemblance to predicted logiKS patterns for natural surfaces that are based on YREE solution chemistry and shale-normalized YREE concentrations in seawater. Yttrium exhibits an itinerant behavior among the REEs: sorption of Y on Fe(III) hydroxide precipitates is intermediate to that of La and Ce, while for Al hydroxide precipitates Y sorption is similar to that of Eu. This behavior of Y can be rationalized from the propensities of different YREEs for covalent vs. ionic interactions. The relatively high shale-normalized concentration of Y in seawater can be explained in terms of primarily covalent YREE interactions with scavenging particulate matter, whereby Y behaves as a light REE, and primarily ionic interactions with solution ligands, whereby Y behaves as a heavy REE.
Rare-earth element (REE) distribution patterns of surface water and commonly also of ground water from industrialised and highly populated areas show anthropogenic gadolinium (Gd) anomalies. They result from the application of organic Gd compounds, such as the derivatives of the gadopentetic acid (Gd-DTPA), as a contrast medium in magnetic resonance imaging. After excretion from the human body, the Gd complex enters the surface water mostly by the effluents of sewage treatment plants. The chemical complex is very stable over at least 6 months under natural conditions. Owing to its anionic state, it is neither adsorbed onto surfaces of abundant clay mineral particles nor by particulate organic matter, both strongly contrasting with the behaviour of the free REE ions. Thus, this complex behaves like a pseudo-natural marker and provides a tool for tracing the mixing of surface and ground water with recycled water, and the infiltration of surface water into aquifers. In urban areas, where water production is commonly based on bank filtration, the anthropogenic Gd of the surface water can be followed to the water production wells. Like boron, δD and δ18O, Gd can be used as a marker in the estimation of the recycled water fraction in ground water systems. Examples of anthropogenic Gd distribution in surface water, sewage and ground water in Berlin, Germany, are discussed. Mixing ratios of bank filtrates and ground water are estimated.
Anthropogenic gadolinium (Gd), used as a contrast agent in magnetic resonance imaging, may enter rivers and groundwaters with the effluents of wastewater treatment plant (WWTP). Such contaminations, which are mainly found in densely populated areas with highly developed medical systems, induce positive gadolinium anomalies in waters. This study reports on the occurrence of positive Gd anomaly in wastewaters, surface and groundwaters in a slightly populated Mediterranean watershed. Water samples have been collected along the Hérault River, in its tributaries, in wells and springs supplying drinking water and in WWTP effluents during two sampling campaigns in February and July 2003. Systematically pronounced positive gadolinium anomalies (Gd/Gd( *)) were observed in WWTP effluents with values reaching 306. These observations have shown that Gd/Gd( *) can also be found in wastewater drained from rural communities, not equipped with MRI facilities. Positive gadolinium anomalies were detected in two tributaries of the Hérault River and in some wells supplying drinking water, corresponding to an excess of anthropogenic Gd in water up to 15.4pM. A monthly monitoring on one well has confirmed the persistence of gadolinium anomalies all along the year, suggesting a continual wastewater contamination on this site. A spatial monitoring on one tributary showed that wastewater contribution modifies completely the normalized REE pattern of river water, resulting in a decrease of REE amount correlated to the Gd anomaly appearance.
An analytical scheme was developed for the determination of Gd-diethylenetriaminepentaacetate (Gd-DTPA), Gd and the other rare earth elements (REE) in river water by inductively coupled plasma (quadrupole) mass spectrometry (ICP-Q-MS). The preconcentration step was essential, since the limits of detection of this multielemental analytical technique are higher than the trace concentrations of the interesting elements in river water. Solid phase extraction (SPE) with different commercially available complexing agents (Chelex 100, Toyopearl and ethylhexylphosphates) was employed for the preconcentration of REE. The investigations revealed that complex stability (varying in dependence of the pH value) has a strong influence on the degree of the enrichment of Gd-DTPA. Based on acidified water samples (pH<3) a procedure using ethylhexylphosphates was proposed for the preconcentration of Gd and REE from surface water samples. For this purpose C(18)-cartridges loaded with ethylhexylphosphates were used, resulting in an enrichment factor of 40.
The behavior of natural and synthetic toxins during bank filtration is commonly investigated either in controlled laboratory experiments or through observations at bank filtration sites. In laboratory batch and column experiments a range of parameters can be varied to assess processes potentially responsible for the elimination of substances. However, hypotheses gained from such experiments need to be verified for field situations. Observations at bank filtration sites are limited to the conditions encountered at such sites, and they are highly dependent on the occurrence of the agents to be assessed in the surface water. For example, cyanotoxins usually occur only during a few weeks of the year. Between the two extremes of laboratory experiments and field observations, controlled field experiments offer an intermediate approach that may substantially improve the understanding of processes relevant in natural systems.
A method for analysing diethylenetriaminepentaacetic acid (DTPA) in pulp and paper mill effluent using ion-interaction reversed-phase liquid chromatography is presented. The analysis is based on formation of the iron(III) complex of DTPA and its separation on a C18 column using 4 mM octylamine in a water-acetonitrile mobile phase. A photodiode array detector is used in the analysis to enable peak purity of the Fe-DTPA peak to be compared between samples and standards. DTPA concentrations ranging from < 1 to 200 mg l−1 may be measured using the technique. Elimination of the FeCl3 reagent in the sample-preparation stage enabled the measurement of DTPA complexed to iron(III). This feature has been used to demonstrate that a significant proportion of the DTPA present in effluent is present in the iron form. The method has been applied to the analysis of DTPA in pulp and paper mill effluent at concentrations ranging from 1 to 20 mg l−1. Recoveries of DTPA spiked into two sets of samples at levels of 2 and 4 mg l−1 averaged 102% with standard deviations of 12 and 16%, respectively. The use of the method to measure DTPA at various locations in the process has indicated that there was a major reduction in the DTPA concentration in pulp and paper mill effluent across the pulping and effluent treatment processes.
The kinetics of transmetallation of Gd3+ in diethylenetriaminpentaacetic acid (Gd-DTPA) by rare earth elements (except Yb), Y3+ and Cu2+ has been studied in test solutions ranging from pH 5 to 6.5 in order to understand the distribution and longevity of their chelates in the hydrosphere. Chelated and non-chelated species were separated by adsorption of the free ions by clay minerals before analysis by ICP-MS. This simple method allows determining the distribution of DTPA chelates at concentration levels as low as a few 10pmol/l. The transmetallation constants at ionic strength of 0.01mol/l and room temperature are commensurable with those derived from published formation constants of the corresponding DTPA complexes. It could be proved that DTPA chelates of rare earth elements, Y and Cu are stable at least over 6 months. The pattern of the second-order rate constants shows a strong tetrad effect, which is not displayed by the pattern of transmetallation constants. Based on these results, the rate of transmetallation of Gd-DTPA under natural conditions is derived. The resultant process yields 10% turn-over of initial Gd-DTPA within two months, if Cu2+ concentrations are below 1nmol/l. At higher concentrations, the turn-over increases with elapsed time. Equilibrium among REE and Y is expected only after tens of years. This makes Gd-DTPA a powerful tracer in hydrological studies.
Because most Southeast Asian basins are flushed rapidly by waters from the western Pacific, the effects of respiration and silica dissolution within those basins are hardly discernible based on general hydrographic and geochemical observations (Broecker et al., 1987). However, a different situation is expected for the Sulu Sea because its deep water is isolated from other deep sea basins by shallow sills of <400 m depth. Hence, any heterogeneity of elemental distributions within the basin must be ascribed to vertical physical and biogeochemical processes. We have obtained detailed vertical profiles of dissolved rare earth elements (REEs) together with conductivity-temperature-depth (CTD) and hydrographic measurements in the Sulu Sea during the 1996–97 Hakuho-Maru cruise. Vertical profiles clearly indicate that the REE(III)s are enriched in the deep water due to regeneration and are involved in vertical biogeochemical cycling. The light REE(III)s (La, Pr, and Nd) showed a subsurface maximum at 500 m and a minimum ∼1500 m in depth. None of the hydrographic properties or nutrients shows such features; therefore, the REE(III)s and their elemental ratios may be useful as tracers of water masses. The relationship of REE(III)s versus dissolved Si suggests that the REE(III)s are regenerated in a delayed fashion relative to Si, and it is likely that their dissolution largely occurs at the bottom interface. The mean residence time of the deep water is estimated to be 300 ± 150 yr. Consequently, the calculated benthic flux of REE(III)s becomes roughly comparable with the river and atmospheric fluxes. Because of oxidation to Ce(IV), the Ce profile shows a decrease from ∼6 pmol/kg at the surface to a constant value at 3.9 pmol/kg below 1500 m, unlike the other REEs. The REEs in the Sulu Sea are enriched in the middle REEs and Ce relative to those of the North Pacific Deep Water and must derive from local sources around the Sulu Sea.
A new filtration method using a 0.04 μm hollow fiber filter was applied to the river, estuarine, and coastal waters in the Chao Phraya estuary for geochemical investigation. The filtered waters were analyzed for all the lanthanides, Y and In by using inductively coupled plasma mass spectrometry (ICPMS). The dissolved concentrations of rare earth elements (REEs) are significantly lower than those reported previously for other rivers, presumably because of effective removal of river colloids by the ultra-filtration. The variation of dissolved REEs in the estuary is dependent on the season. The light REEs vary considerably in the low salinity (S < 3) zone presumably due to adsorption–desorption interaction with suspended particles. In January when the river discharge is low, the REEs show maxima in the mid salinity (S = 5–12) zone suggesting that dissolved REEs are supplied to the waters by either desorption from suspended loads or remineralization of underlying sediments. The rapid removal of the REEs is also taking place in the turbid-clear water transition zone (S = 12–15), presumably due to biological uptake associated with blooming of Noctilca occurred at the time of January sampling. In the medium to high discharge season (July and November), the dissolved REE(III)s at S > 3 show almost conservative trends being consistent with some of the previous works. Europium is strongly enriched in the river and estuarine waters compared to the South China Sea waters. Thus, the REE source of the Chao Phraya River must be fractionated and modified in entering to the South China Sea. Dissolved In and Ce in the high salinity (S = 20–25) zone of the estuary are lower than those of the offshore waters, and therefore, the dissolved flux of the Chao Phraya River cannot account for the higher concentrations of dissolved In and Ce in the surface waters of the South China Sea. The negative Ce anomaly is progressively developed with increasing salinity, being consistent with continued oxidation of Ce(III) to Ce(IV) in the estuary. Fractionation of the light-to-heavy REEs seems to take place, whereas the Y/Ho fractionation is unclear in the estuarine mixing zone.
The gas chromatographic (GC) and the liquid chromatographic (HPLC) methods were applied to the determination of the ethylenediaminetetraacetic acid (EDTA) and the diethylenetriaminepentaacetic acid (DTPA) in waste water effluents of pulp and paper mills. The waste waters of the six pulp and paper mills of different bleaching sequences were investigated. In the effluents EDTA and DTPA were found at the concentrations ranging between 0.24-8.4 mg/1 and 0.51-9.2 mg/l, respectively. Preliminary results of the reduction of EDTA (17–30 %) and DTPA (54–68 a/o) in waste water treatment plants are also presented.
The rate of photolysis of iron complexes with three common complexing agents, NTA, EDTA and DTPA was analysed. Aqueous solutions of each complex were illuminated in a Xenotest 1200. Using a sun spectrum from 60°N (Stockholm latitude), environmentally related half lifetimes were calculated.The half lifetimes were 43, 11 and 8 min for the three 1:1 complexes, resp., dissolved in the top layer of a water system and illuminated at the yearly maximum of sun light in the specified area. In the environment several factors operate to reduce this rate. However, photolytic degradation pathways seem to be an important environmental fate of these substances.
Tracer tests provide highly valuable information about the transport properties of saturated rocks which is essential to the characterization of a potential radioactive waste repository site. In the frame of El Berrocal project, a set of tracer tests was performed in a complex geometry of inclined boreholes, combined with highly fractured transmissive zones. The aims of the tracer test programme were to gain experience, knowledge and insight into field transport experiments. To achieve this a detailed programme of new instrumentation design, site characterization and laboratory tasks was developed. For field monitoring a new electronic system was developed. The system is able to measure up to 256 parameters per borehole, with surface equipment to control pumping rates and physical and chemical parameters at both injection and extraction boreholes. The experiments progressed from single borehole dilution tests under both natural flow and forced gradient conditions to convergent flow tracer tests. Dilution tests helped to discriminate the most suitable borehole sections at which to inject tracers. The tracers were selected by the results of the laboratory programme. Uranine (fluorescein), DTPA-gadolinium (diethylenetriaminopentacetic acid, gadolinium (III)), and deuterium were injected simultaneously in one borehole section and recovered at another borehole 20 m away, pumping at a flowrate of 0.1 1 min−1. First results showed a thickness porosity of 1.2 × 10−3 m and a longitudinal dispersivity of 17.0 m using uranine data acquired over a period of 4 d, at which point the recovery concentration had reached a maximum. However, gadolinium and deuterium appeared to travel faster, arriving at peak values after only 2 d of injection.
Ethylenediamine tetraacetic acid (EDTA) and diethylenetriamine pentaacetic acid (DTPA) are synthetic chelating agents that form stable complexes with most metals and are used in a variety of industrial applications. They are increasingly used with peroxide and ozone bleaching of wood pulp to sequester iron and manganese. These chelates have been widely reported to either resist degradation or undergo slow biodegradation. EDTA and DTPA have few known environmental impacts in receiving waters.A study was conducted to assess the biodegradability of EDTA and DTPA and to determine if these compounds could be transformed in conventional effluent treatment processes. Four dissimilar inocula were used in batch and continuous aerobic tests using a variety of enrichment techniques. Selection pressure was applied to bacterial populations by providing EDTA and DTPA as sole carbon sources. Additionally, experiments were conducted using degraders of chemically similar compounds nitrilotriacetic acid and triethanolamine. In all experiments, the results showed that neither EDTA or DTPA are biodegraded under aerobic conditions.
Rare earth element (REE) concentrations were measured in 5 well water samples and 3 springs located along a groundwater flow path in a shallow, tuffaceous alluvial aquifer from southern Nevada, USA. The REE concentrations in these groundwaters decrease in the direction of groundwater flow. A previous investigation demonstrated that REE solid-liquid phase partitioning coefficients (i.e., Kd’s) for groundwaters from tuffaceous alluvial aquifers in southern Nevada are relatively high (mean Kd = 102.6). Our groundwater REE data, in conjunction with these Kd’s, support strong sorption of aqueous REEs to aquifer surface sites as the primary removal mechanism of REEs from these groundwaters. In addition, relatively high aqueous REE concentrations occur at distinct locations along the groundwater flow path. The elevated REE concentrations are explained by addition of deeper groundwaters, influx of geothermal waters from a hot spring system, differences in solution complexation, and/or mixtures of regional and local recharge sources. Solution complexation modelling of REEs in the groundwaters indicate that carbonate complexes account for more than 99% of each REEs in solution. Moreover, groundwater Yb/Nd ratios (a measure of REE fractionation) are associated with alkalinity (HCO3− + CO32−; r = 0.71). The data and speciation model results indicate that REE fractionation (i.e., the observed heavy REE, HREE, enrichments compared to rock-sources) is controlled by formation of progressively stronger carbonate complexes in solution with increasing atomic number, which inhibits HREE sorption compared to light REEs (LREE); and a greater affinity for the LREEs to sorb to surface sites in the local tuffaceous alluvial aquifers compared to the HREEs.
Concentrations of the rare earth elements (REE) were measured in circumneutral pH groundwaters from southern Nevada and Death Valley, CA. Groundwaters from the regional lower Paleozoic carbonate-rock aquifer (Cambrian–Devonian) have flat shale-normalized patterns that closely resemble the shale-normalized patterns of the aquifer rock samples (principally Cambrian). Groundwaters associated with younger carbonate rocks (chiefly Permian) in the study region exhibit heavy REE (HREE) enriched, shale-normalized REE patterns with substantial negative Ce anomalies that also mimic these carbonate rocks. In addition, groundwaters from the felsic volcanic rock aquifers have the same flat to light REE (LREE) enriched shale-normalized patterns with large negative Eu anomalies as the felsic volcanic rocks. The similar REE patterns of all the groundwaters and associated aquifer rocks studied suggest that the groundwaters inherited REE signatures from the host rocks through which they flow. Because negative Ce anomalies are not an uncommon feature of carbonate rocks of marine origin, the negative Ce anomalies reported here for these groundwaters may reflect a Permian marine Ce signature. Previously, we demonstrated that carbonate complexes dominate REE speciation in southern Nevada and Death Valley groundwaters. Moreover, solid–liquid partitioning coefficients (Kd) indicate that the affinity of LREEs to sorb to aquifer surface sites is substantially greater than for the HREEs in the southern Nevada carbonate- and felsic volcanic-rock alluvial aquifers. Consequently, the HREEs enrichments reported here for groundwaters associated with younger Paleozoic carbonate rocks compared to these source rocks is consistent with REE carbonate complexation and preferential removal of LREEs to aquifer surface sites.
Standard reference water samples (SRWS) were collected from two mine sites, one near Ophir, CO, USA and the other near Redding, CA, USA. The samples were filtered, preserved, and analyzed for rare earth element (REE) concentrations (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) by inductively coupled plasma-mass spectrometry (ICP-MS). These two samples were acid mine waters with elevated concentrations of REEs (0.45–161 μg/l). Seventeen international laboratories participated in a ‘round-robin’ chemical analysis program, which made it possible to evaluate the data by robust statistical procedures that are insensitive to outliers. The resulting most probable values are reported. Ten to 15 of the participants also reported values for Ba, Y, and Sc. Field parameters, major ion, and other trace element concentrations, not subject to statistical evaluation, are provided.
Rare earth patterns of surface and groundwaters near big cities often show anthropogenic Gd (Gd(ant)) anomalies in addition to geogenic Ce and Y anomalies. The Gdant anomaly is caused by very stable organic complexes, one of which is gadopentetic acid, Gd-DTRA. Derivatives of this and similar compounds are used as contrast agents in magnetic resonance imaging (MRI) of the human blood system. The organic Gd complexes are stable enough to pass nearly unaffected through sewage treatment plants and are, thereafter, discharged into surface water systems. Water of the rapidly flowing Isarco/Eisack and Adige/Etsch rivers (Provinces of Trento and Bolzano/Bozen, NE Italy) and their tributaries show remarkable variations in anthropogenic Gd contents (Gd(ant)). Low Gd(ant) values are found on Monday and Tuesday, whereas high values are observed during the remaining weekdays. Reliable Gd(ant) balances are calculated for the river system at the confluence of the Adige and its tributaries. At two places local decrease of Gd(ant) indicates exfiltration of groundwater. It is demonstrated that Gd(ant) can be used as a reliably conservative tracer to study the water budget in rapidly flowing alpine river systems. The studied different river waters show considerable negative Ce and positive Y anomalies. Negative Ce anomalies are caused by scavenging of Ce(III) by FeO(OH) precipitates and subsequent oxidation to CeO(2).Y anomalies are attributed to less sorption of Y than REE onto particulate matter. Thus, Y moves faster than REE. Both, Ce and Y anomalies, are of geogenic origin.
“Anthropogenic” gadolinium, Gd, used in contrast agents in magnetic resonance imaging, is a micropollutant that enters river and lake waters with the discharge from wastewater treatment plants, WWTPs. Such discharge is also the source of other micropollutants, for example pharmaceuticals, such as steroids, antihistamins, and antibiotics. Together with the “natural” Gd, the anthropogenic Gd produces positive Gd anomalies in rare-earth element distribution patterns and is, therefore, easily detectable. This pilot study reports on the occurrence of anthropogenic Gd in rivers in Pennsylvania (Ohio, Beaver, Allegheny, Monongahela, Juniata, and Susquehanna) and in near-shore surface water from Lake Erie close to the city of Buffalo. Additional data are reported for the Delaware River and the headwaters of Spring Creek in Central Pennsylvania, and for Lake Ontario and Niagara River, all of which do not show significant anthropogenic Gd. Most pronounced impact of anthropogenic Gd discharged from WWTPs is observed in the Pittsburgh Metropolitan area. Such contamination is similar to that observed in densely populated areas with highly developed medical and healthcare systems in Europe and Japan. Its worldwide applicability adds to the promising potential of anthropogenic Gd as a cost-effective tracer for the presence of WWTP effluent in river, lake, ground, and drinking waters.
The concentrations of EDTA and DTPA were measured by gas chromatography in Finnish lake waters and sediments influenced by pulp and paper industry. Concentrations of EDTA in lake water ranged from <1.0 to 11.4 μ/1. Elevated concentrations of EDTA were observed downstream of the mills. The decline in the use of EDTA in total-chlorine-free (TCF) processes is clearly shown by decreased waste water and lake water concentrations of EDTA. Sediment concentrations of EDTA varied between 80 and 310 μg/kg. In contrast to EDTA, DTPA was not found in lake waters and sediments.
The concurrent exchange of REE3+ and Y3+ (combined to M3+) and Cu2+ for Gd3+ in Gd-DTPA (Gd-diethylenetriaminepentaacetic acid or gadopentetic acid) in the presence of clay is a very slow process if the concentrations of M3+, Cu2+ and Gd-DTPA in solution are in the range of 0.01–22 nmol/L. The kinetics of transmetallation was followed for 1033 h without reaching equilibrium, although the release of metal ions from the clay pool is a fast process. The sum of all newly formed mono-nuclear M-DTPA species is less than the difference [Gd-DTPAo] − [Gd-DTPA] even after 1033 h but the sum of all derived M-DTPA + Cu-DTPA chelates exceeds this difference indicating that within this time span poly-nuclear chelates of Cu also formed. Formation of CuGd-DTPA chelates is the fastest process followed by formation of less stable MGd-DTPA chelates. With progress of formation of CuGd-DTPA the concentration of Gd-DTPA is lowered and consequently MGd-DTPA decomposes. Furthermore Cu2+ reacts with MGd-DTPA to form CuM-DTPA. The observed rate constants vary from species to species, whereas the pseudo-first-order-rate constants kM are nearly the same for all lanthanides. The observed rate constant for kCu exceeds those of kM because Cu concentrations are higher than M. The changes in M speciation under the influence of DTPA are estimated for a typical composition of surface water. Input of Gd-DTPA leaves only La and, to a lesser degree, Ce unaffected by transmetallation. The total concentrations of both Cu and intermediate to heavy REE increase, whereas total Gd decreases because released Gd3+ is adsorbed by clay minerals. Depending on Cu2+ and GdL2− concentrations in natural surface and groundwaters, Gd-DTPA decreases by about 10% within a year. Equilibrium is theoretically reached only after more than 70 a.
Tracers are used widely to determine the direction and velocity of ground-water movement. Failures of tracer tests are most commonly a result of incorrect choice of tracers, insufficient concentrations of tracers, and a lack of an understanding of the hydrogeologic system being tested. Some of the most useful general tracers are bromide chloride, rhodamine WT, and various fluorocarbons. For certain purposes, dyed clubmoss and baker's yeast have proved valuable. Many radionuclides including 3H, 82Br, and 198Au are almost ideal for numerous purposes, but radiation hazards associated with their use together with local, State, and Federal regulations have discouraged widespread field applications in recent years within the United States.
Studies of the stability of various metal EDTA, DTPA and DOTA complexes in order to evaluate their applicability as non-sorbing
tracers have been performed. In laboratory tests, the stability generally increases for the individual metal ions in the EDTA<DTPA<DOTA
order. For most metal ions, the same trend can be observed for the thermodynamic stability constants. In the in situ experiment,
various metal EDTA tracers were used in very low concentrations; YbEDTA−, for example had a breakthrough and recovery which were very similar to the non-sorbing tracers used. According to the extremely
low tracers concentrations used, thermodynamic data indicate that all metal EDTA tracers should have been decomplexed as a
result of the competition with the naturally occurring cations in the groundwater. This was not found, which indicates that
the decomplexation rate and sorption mechanism are important in estimating the applicability of the metal complexes as tracers.
The DOTA complexes of elements in the middle of the lanthanide series have indicated high stability in the laboratory tests
and therefore appear to be good candidates as non-sorbing tracers. However, in contrary to the metal EDTA, tracers, the DOTA
complexes of La3+ and Lu3+ seemed to be slightly delayed in the in situ experiment.
All major rivers in northwestern Germany that flow into the North Sea, including the Weser River, display rare earth element (REE) patterns with large positive gadolinium (Gd) anomalies that indicate the presence of anthropogenic Gd derived from contrast agents used in magnetic resonance imaging. This microcontaminant cannot be removed by common sewage treatment technology and enters rivers and lakes with the discharge from waste water treatment plants. As elsewhere, a large fraction of the natural dissolved REE in the Weser River are associated with colloids. These colloids aggregate during mixing of freshwater and seawater in the low-salinity part of the Weser Estuary and the dissolved REE are partially removed from the river water together with the colloids. In marked contrast to the natural REE, the anthropogenic Gd behaves conservatively during this estuarine mixing and transits through the Weser Estuary almost unaffected. This indicates that the speciation of anthropogenic Gd is different from that of natural Gd and suggests a long environmental half-life of the anthropogenic Gd complexes used as contrast agents. The amount of anthropogenic Gd introduced into seawater via rivers is significant and produces anthropogenic positive Gd anomalies in coastal seawater. This is observed in the southwestern North Sea, off the coast of the East Frisian Islands, where anthropogenic Gd is mostly derived from the rivers Rhine and Thames. Its long environmental half-life and conservative estuarine behaviour suggest that anthropogenic Gd might be utilized as a pseudo-natural far-field tracer for truly dissolved riverine REE input into seawater and for discharge from waste water treatment plants and for sewage in river, ground and drinking water. The widespread distribution of anthropogenic Gd is an example of how the increasing use of "exotic" (ultra)trace elements in high-tech processes will in the future significantly hamper studies of the distribution and geochemical behaviour of such elements in natural systems.
Experiments were conducted to evaluate the impact of organic complexation on the development of Ce anomalies and the lanthanide tetrad effect during the adsorption of rare-earth elements (REE) onto MnO2. Two types of aqueous solutions—NaCl and NaNO3—were tested at pH 5 and 7.5. Time-series experiments indicate that a steady-state is reached within less than 10 h when REE occur as free inorganic species, whereas steady state is not reached before 10 d when REE occur as REE-humate complexes. The distribution coefficients (KdREE) between suspended MnO2 and solution show no or only very weak positive Ce anomaly or lanthanide tetrad effect when REE occur as humate complexes, unlike the results obtained in experiments with REE occurring as free inorganic species. Monitoring of dissolved organic carbon (DOC) concentrations show that log KdREEorganic/KdDOC ratios are close to 1.0, implying that the REE and humate remain bound to each other upon adsorption. Most likely, the Ce anomaly reduction/suppression in the organic experiments arises from a combination of two processes: (i) inability of MnO2 to oxidize Ce(III) because of shielding of MnO2 surfaces by humate molecules and (ii) Ce(IV) cannot be preferentially removed from solution due to quantitative complexation of the REE by organic matter. We suggest that the lack of lanthanide tetrad effect arises because the adsorption of REE-humate complexes onto MnO2 occurs dominantly via the humate side of the complexes (anionic adsorption), thereby preventing expression of the differences in Racah parameters for 4f electron repulsion between REE and the oxide surface. The results presented here explain why, despite the development of strongly oxidizing conditions and the presence of MnO2 in the aquifer, no (or insignificant) negative Ce anomalies are observed in organic-rich waters. The present study demonstrates experimentally that the Ce anomaly cannot be used as a reliable proxy of redox conditions in organic-rich waters or in precipitates formed at equilibrium with organic-rich waters.
New data on the dissolved (<0.04 μm) rare earth elements (REEs) and In in the Japanese Ara, Tama, and Tone river-estuaries and Tokyo Bay are presented. Unique shale-normalized REE patterns with a distinct positive Gd anomalies and a strong heavy-REE enrichment were seen throughout the data. The dissolved Gd anomaly is caused by local anthropogenic input mainly due to recent use of Gado-pentetic acid as a medical agent for magnetic resonance imaging (MRI) in hospitals. The heavy-REE enrichment may be attributed to fractionation during weathering and transport in the upstream of the rivers, and only partially to removal of light- and middle-REE enriched river colloids by the use of a new ultrafiltration technique. Dissolved In concentrations in the Japanese rivers are extraordinarily high as compared to those in the pristine Chao Phraya river of Thailand reported elsewhere (Nozaki et al., in press). Like Gd, the high dissolved In in the study area can also be ascribed to recent use of In-containing organic compound, In(DTPA)2− in medical diagnosis. Thus, in the highly populated and industrialized area, dissolved heavy metal concentrations in rivers and estuaries may be significantly perturbed by human activities and the fate of those anthropogenic soluble substances in the marine environment needs to be investigated further.
Experiments were carried out to investigate the sorption of the complete lanthanide series (Ln or rare earth elements, REE) on a kaolinite and an a Na-montmorillonite at 22°C over a wide range of pH (3–9). Experiments were conducted at two ionic strengths, 0.025 and 0.5 M, using two different background electrolytes (NaNO3 or NaClO4) under atmospheric conditions or N2 flow (glove box). The REE sorption does not depend on the background electrolyte or the presence of dissolved CO2, but is controlled by the nature of the clay minerals, the pH and the ionic strength. At 0.5 M, both clay minerals exhibit the same pH dependence for the Ln sorption edge, with a large increase in the sorption coefficient (KD) above pH 5.5. At 0.025 M, the measured KD is influenced by the Cation Exchange Capacity (CEC) of the minerals. Two different behaviours are observed for smectite: between pH 3 and 6, the KD is weakly pH-dependent, while above pH 6, there is a slight decrease in log KD. This can be explained by a particular arrangement of the particles. For kaolinite, the sorption coefficient exhibits a linear increase with increasing pH over the studied pH range. A fractionation is observed that due to the selective sorption between the HREEs and the LREEs at high ionic strength, the heavy REE is being more sorbed than the light REE. These results can be interpreted in terms of the surface chemistry of clay minerals, where two types of surface charge are able to coexist: the permanent structural charge and the variable pH-dependent charge. The fractionation due to sorption observed at high ionic strength can be interpreted either because of a competition with sodium or because of the formation of inner-sphere complexes. Both processes could favour the sorption of HREEs according to the lanthanide contraction.
Multidentate chelating agents such as NTA, EDTA and DTPA are receiving widespread use in a variety of industrial applications and are entering natural water systems. The presence of these chelates in the environment can be undesirable because they solubilise toxic heavy metals. We have analysed the relative biodegradabilities of NTA, EDTA and DTPA in several different chemical environments. The objective was to determine whether any particular chelate is significantly more biodegradable than the others and therefore more desirable from an environmental point of view.Our results suggest that total degradation (including biological and non-biological) rates decrease in the order: DTPA > EDTA > NTA over the short term and NTA ∼ DTPA > EDTA over the long term. However, photolysis appeared to account for a significant proportion of DTPA degradation. Therefore, considering only biodegradation: NTA > EDTA ∼ DTPA. Degradation rates of all three chelates are not rapid enough, even under ideal laboratory conditions, to preclude concern about their release to the environment.
Scavenging experiments were performed at pH 3.6 to 6.2 with synthetic solutions containing dissolved Fe (≈7 mg/L), Rare Earths and Yttrium (ΣREY: ≈61 μg/L) in a matrix of 0.01 M HCl, and with natural water from Nishiki-numa spring, Japan, with the aim to study the fractionation that results from the interaction of dissolved REY with precipitating Fe oxyhydroxide. All patterns of apparent REY distribution coefficients between Fe oxyhydroxide and solution, appDREY, show negative anomalies at Y, La, and Gd, and the M-type lanthanide tetrad effect. These features become more pronounced with increasing pH. At pH ≤ 4.6, positive anomalies of appDCe give evidence for oxidative scavenging of Ce on the Fe oxyhydroxide. A time-series experiment at pH 3.5 suggests that a stationary exchange equilibrium for the REY(III) is reached within less than 6.5 min, whereas the Ce(IV)/Ce(III) redox-equilibrium is not attained before 120 min. Oxidation rates of Ce(III) were found to decrease significantly during the first minutes after Fe oxyhydroxide formation, indicating that the capacity for Ce(III) oxidation is drastically higher in systems in which fresh Fe oxyhydroxides precipitate than in systems in which dissolved REY interact with pre-formed Fe oxyhydroxides. This additionally complicates the use of Ce anomalies of natural precipitates as quantitative paleo-redox-proxies. Radius-independent fractionation of REY(III) is very similar in experiments using synthetic solutions and natural water, despite the additional precipitation of hydrous Al oxides from the latter. Because there is no change of solution-complexation (speciation) along the REY series, radius-independent fractionation of REY(III) is likely due to differences between the stabilities of surface-complexes of the individual members of the REY series. The results presented here are an experimental verification of a natural process that may produce the lanthanide tetrad effect in geological samples.
Positive Gd anomalies in shale-normalised rare earth element (REESN) patterns of natural waters may provide information on the types of ligands which control surface complexation of REE on particle surfaces. However, REESN patterns of rivers which drain densely populated and industrialised areas in Central Europe and North America are characterised by pronounced positive GdSN anomalies, whereas rivers in thinly populated, non-industrialised areas in Värmland and Dalarna, central Sweden, and Hokkaido, Japan, do not show such anomalies. Acidification experiments suggest that, unlike the other REE, the excess Gd found in German rivers is almost completely related to the ‘dissolved’ REE fraction (< 0.2 μm) in a water sample and not to the acid-soluble particulate fraction, suggesting a negligible particle reactivity of the excess Gd. The positive GdSN anomalies are of anthropogenic origin and are most likely to result from the application of gadopentetic acid, Gd(DTPA)2−, in magnetic resonance imaging (MRI). In MRI, gadopentetic acid, which is an organic aqueous Gd(III) complex with very high stability constant, is used as a paramagnetic contrast agent. Since positive GdSN anomalies in rivers, lakes, semi-closed sea basins, and coastal seas, which receive riverine REE input from industrialised, densely populated areas may (partly) be of anthropogenic origin, the positive GdSN anomaly can no longer be used as a natural geochemical indicator.
Biological degradability of ethylenediamine derivatives depends on the type and number of substituents. The susceptibility to biodegradation decreases in the sequence of substituents -COCH3, -CH3, -C2H5, -CH2CH2OH, -CH2COOH and with polysubstitution. The biodegradability depends also on the kind and number of nitrogen atoms. Complexing agents with a single-nitrogen atom in the molecule (e.g. NTA) succumb relatively readily to biodegradation whereas, compounds with two or more tertiary amino groups are biologically highly stable and do not undergo biodegradation even in experiments with activated sludge adapted at an age of up to 30 days (EDTA, DTPA, PDTA, HEDTA). A lowering of the degree of substitution brings about an increased susceptibility to biodegradation. This holds, e.g., for replacement of tertiary amino groups with secondary ones; thus the symmetrically disubstituted ethylenediamine-N,N'-diacetic acid (EDDA) possesses still sufficient complexing ability while belonging already to the group of potentially degradable substances.
The biological degradability (Zahn-Wellens test) of ethylenediamine derivatives with carboxymethyl and 2-hydroxyethyl groups was investigated. Mixed bacterial culture (activated sludge) was used as inoculum (non-adapted sludge and sludge adapted at different mean biomass retention time, the so-called sludge age). Biodegradability of ethylene(propylene)di(tri)amine-based complexing agents depends on the character and number of substituents and nitrogen atoms in the molecule. Tetra(penta)substituted derivatives with two or more tertiary nitrogen atoms and carboxymethyl or 2-hydroxyethyl groups in the molecule (EDTA, DTPA, PDTA, HEDTA) are very stable from an environmental point of view. On the contrary, disubstituted derivatives with two secondary nitrogen atoms in the molecule (e.g., EDDA) are potentially degradable.
This study reports a pronounced positive Gd anomaly in a small river and in the largest French Mediterranean lagoon. Along the studied catchment, this anomaly is also present in the effluents of the municipal sewage treatment plants, suggesting an anthropogenic origin for the Gd excess. The anomaly corresponds to a distinct increase of Gd concentrations (up to 19 pmol/l) in the river and around 5.4 pmol/l in the lagoon. The excess flux of Gd is compatible with the medical use of water soluble Gd complexes as contrasting agent in magnetic resonance imaging.
The anthropogenic Gd (Gdant) loads and fluxes of surface- and groundwaters, and of effluents from sewage treatment plants of Prague and its surroundings, have been determined. While passing Prague the Gdant load of the Vltava river increases from 4.5 to 19.2 nmol/m3, which is caused by the effluents of the central sewage treatment plant with a 6 day average of 250 nmol/m3. The Berounka river with its enhanced content doubles the Gdant flux of the Vltava river before entering Prague. All minor creeks draining Prague add less than 3% of the Gdant load in the Vltava river downstream of Prague. The 11-days average of the amount of the administered Gd complexes of the gadopentetic acid (Gd-DTPA), gadobenic acid, and other compounds in Prague's hospitals (22 g-Gdant/d) exceeds the 6 days average of 15 g-Gdant/d in the effluent of the central sewage treatment plant. This strongly indicates uncontrolled losses of sewage from sewers to the groundwater.
In many surface waters, sewage treatment plant (STP) effluent is a substantial source of both regulated and unregulated contaminants, including a suite of complex organic compounds derived from household chemicals, pharmaceuticals, and industrial and medical byproducts. In addition, STP effluents in some urban areas have also been shown to have a positive gadolinium (Gd) anomaly in the rare earth element (REE) pattern, with the Gd derived from its use in medical facilities. REE concentrations are relatively easy to measure compared to many organic wastewater compounds and may provide a more widely utilized tracer of STP effluents. To evaluate whether sewage treatment plant-associated Gd is a useful tracer of treatment plant effluent, an investigation of the occurrence, fate, and transport of rare earth elements was undertaken. The rare earth element patterns of four of five STP effluents sampled display positive Gd anomalies. The one site that did not have a Gd anomaly serves a small community, population 1200, with no medical facilities. Biosolids from a large metropolitan STP are not enriched in Gd even though the effluent is, suggesting that a substantial fraction of Gd remains in the aqueous phase through routine treatment plant operation. To evaluate whether STP-derived Gd persists in the fluvial environment, a 14-km study reach downstream of an STP was sampled. Gadolinium anomalies were present at all five downstream sites, but the magnitude of the anomaly decreased. Effluent from STPs is a complex mixture of organic and inorganic constituents, and to better understand the chemical interactions and their effect on REEs, the aqueous speciation was modeled using comprehensive chemical analyses of water samples collected downstream of STP input. These calculations suggest that the REEs will likely remain dissolved because phosphate and carbonate complexes dominate over free REE ions. This study supports the application of Gd anomalies as a useful tracer of urban wastewater.
Rare earth elements fractionation and concentration variation along a ground water flow path within shallow, basin fill aquifer
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Elimination of microcystins by slow sand filtration at the UBA experimental field Riverbank filtration: understanding contaminant biogeochemistry and pathogen removal The Netherlands
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Simulating bank filtration and artificial recharge on a technical scale
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