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At least 181 records · Page 10Linked to original sources
USGS2019

Constraining the oxygen isotopic composition of nitrate produced by nitrification

Measurements of the stable isotope ratios of nitrogen ( 15 N/ 14 N) and oxygen ( 18 O/ 16 O) in nitrate (NO 3 – ) enable identification of sources, dispersal, and fate of natural and contaminant NO 3 – in aquatic environments. The 18 O/ 16 O of NO 3 – produced by nitrification is often assumed to reflect the proportional contribution of oxygen atom sources, water, and molecular oxygen, in a 2:1 ratio. Culture and seawater incubations, however, indicate oxygen isotopic equilibration between nitrite (NO 2 – ) and water, and kinetic isotope effects for oxygen atom incorporation, which modulate the NO 3 – 18 O/ 16 O produced during nitrification. To investigate the influence of kinetic and equilibrium effects on the isotopic composition of NO 3 – produced from the nitrification of ammonia (NH 3 ), we incubated streamwater supplemented with ammonium (NH 4 + ) and increments of 18 O-enriched water. Resulting NO 3 – 18 O/ 16 O ratios showed (1) a disproportionate sensitivity to the 18 O/ 16 O ratio of water, mediated by isotopic equilibration between water and NO 2 – , as well as (2) kinetic isotope discrimination during O atom incorporation from molecular oxygen and water. Empirically, the NO 3 – 18 O/ 16 O ratios thus produced fortuitously converge near the 18 O/ 16 O ratio of water. More elevated NO 3 – 18 O/ 16 O values commonly reported in soils and oxic groundwater may thus derive from processes additional to nitrification, including NO 3 – reduction.

Environmental Science & Technology↗
USGS2018

Human-associated indicator bacteria and human-specific viruses in surface water: a spatial assessment with implications on fate and transport

Hydrologic, seasonal, and spatial variability of sewage contamination was studied at six locations within a watershed upstream from water reclamation facility (WRF) effluent to define relative loadings of sewage from different portions of the watershed. Fecal pollution from human sources was spatially quantified by measuring two human-associated indicator bacteria (HIB) and eight human-specific viruses (HSV) at six stream locations in the Menomonee River watershed in Milwaukee, Wisconsin from April 2009 to March 2011. A custom, automated water sampler, which included HSV filtration, was deployed at each location providing unattended, flow-weighted, large-volume (30-913 L) sampling. In addition, wastewater influent samples were composited over discrete seven-day periods from the two Milwaukee WRFs. Of the eight HSV only three were detected, present in up to 38% of the 228 stream samples, while at least one HSV was detected in all WRF influent samples. HIB occurred more often with significantly higher concentrations than the HSV in stream and WRF influent samples (p<0.05). HSV yield calculations showed a loss from upstream to the most downstream sub-watershed of the Menomonee River, and in contrast, a positive HIB yield from this same sub-watershed emphasizes the complexity in fate and transport properties between HSV and HIB. This study demonstrates the utility of analyzing multiple HSV and HIB to provide a weight of evidence approach for assessment of fecal contamination at the watershed level, provides an assessment of relative loadings for prioritizing areas within a watershed, and demonstrates how loadings of HSV and HIB can be inconsistent, inferring potential differences in fate and transport between the two indicators of human fecal presence.

Wisconsin↗
USGS2018

Toxicity assessment of groundwater contaminated by petroleum hydrocarbons at a well-characterized, aged, crude oil release site

Management of petroleum-impacted waters by monitored natural attenuation requires an understanding of the toxicology of both the original compounds released and the transformation products formed during natural breakdown. Here, we report data from a groundwater plume consisting of a mixture of crude oil compounds and transformation products in an effort to bridge the gap between groundwater quality information and potential biological effects of human exposures. Groundwater samples were characterized for redox processes, concentrations of nonvolatile dissolved organic carbon (NVDOC) and total petroleum hydrocarbons in the diesel range, as well as for activation of human nuclear receptors (hNR) and toxicologically relevant transcriptional pathways. Results show upregulation of several biological pathways, including peroxisome proliferator-activated receptor gamma and alpha, estrogen receptor alpha, and pregnane X receptor (PXR) with higher levels of hNR activity observed in more contaminated samples. Our study of affected groundwater contaminated by a crude-oil release 39 years ago shows these types of waters may have the potential to cause adverse impacts on development, endocrine, and liver functioning in exposed populations. Additionally, positive trends in activation of some of the molecular targets (e.g., PXR) with increasing NVDOC concentrations (including polar transformation products) demonstrate the importance of improving our understanding of the toxicity associated with the unknown transformation products present in hydrocarbon-impacted waters. Our results begin to provide insight into the potential toxicity of petroleum-impacted waters, which is particularly timely given the ubiquitous nature of waters impacted by petroleum contamination not only recently but also in the past and the need to protect drinking-water quality.

Environmental Science & Technology↗
USGS2018

Elevated manganese concentrations in United States groundwater, role of land surface–soil–aquifer connections

Chemical data from 43 334 wells were used to examine the role of land surface–soil–aquifer connections in producing elevated manganese concentrations (>300 μg/L) in United States (U.S.) groundwater. Elevated concentrations of manganese and dissolved organic carbon (DOC) in groundwater are associated with shallow, anoxic water tables and soils enriched in organic carbon, suggesting soil-derived DOC supports manganese reduction and mobilization in shallow groundwater. Manganese and DOC concentrations are higher near rivers than farther from rivers, suggesting river-derived DOC also supports manganese mobilization. Anthropogenic nitrogen may also affect manganese concentrations in groundwater. In parts of the northeastern U.S. containing poorly buffered soils, ∼40% of the samples with elevated manganese concentrations have pH values < 6 and elevated concentrations of nitrate relative to samples with pH ≥ 6, suggesting acidic recharge produced by the oxidation of ammonium in fertilizer helps mobilize manganese. An estimated 2.6 million people potentially consume groundwater with elevated manganese concentrations, the highest densities of which occur near rivers and in areas with organic carbon rich soil. Results from this study indicate land surface–soil–aquifer connections play an important role in producing elevated manganese concentrations in groundwater used for human consumption.

Environmental Science & Technology↗
USGS2018

Linking the agricultural landscape of the Midwest to stream health with structural equation modeling

Multiple physical and chemical stressors can simultaneously affect the biological condition of streams. To better understand the complex interactions of land-use practices, water quality, and ecological integrity of streams, the U.S. Geological Survey National Water Quality Assessment Project is conducting regional-scale assessments of stream condition across the United States. In the summer of 2013, weekly water samples were collected from 100 streams in the Midwestern United States. Employing watershed theory, we used structural equation modeling (SEM) to represent a general hypothesis for how 16 variables (previously identified to be important to stream condition) might be inter-related. Again, using SEM, we evaluated the ability of this “stressor network” to explain variations in multimetrics of algal, invertebrate, and fish community health, trimming away any environmental variables not contributing to an explanation of the ecological responses. Seven environmental variables—agricultural and urban land use, sand content of soils, basin area, percent riparian area as forest, channel erosion, and relative bed stability—were found to be important for all three-community metrics. The algal and invertebrate models included water-chemistry variables not included in the fish model. Results suggest that ecological integrity of Midwest streams are affected by both agricultural and urban land uses and by the natural geologic setting, as indicated by the sand content of soils. Chemicals related to crops (pesticides and nutrients) and residential uses (pyrethroids) were found to be more strongly related to ecological integrity than were natural factors (riparian forest, watershed soil character).

Environmental Science & Technology↗
USGS2019

Fungicides: An overlooked pesticide class?

Fungicides are indispensable to global food security and their use is forecasted to intensify. Fungicides can reach aquatic ecosystems and occur in surface water bodies in agricultural catchments throughout the whole growing season due to their frequent, prophylactic application. However, in comparison to herbicides and insecticides, the exposure to and effects of fungicides have received less attention. We provide an overview of the risk of fungicides to aquatic ecosystems covering fungicide exposure (i.e., environmental fate, exposure modelling, and mitigation measures) as well as direct and indirect effects of fungicides on microorganisms, macrophytes, invertebrates, and vertebrates. We show that fungicides occur widely in aquatic systems, that the accuracy of predicted environmental concentrations is debatable, and that fungicide exposure can be effectively mitigated. We additionally demonstrate that fungicides can be highly toxic to a broad range of organisms and can pose a risk to aquatic biota. Finally, we outline central research gaps that currently challenge our ability to predict fungicide exposure and effects, promising research avenues, and shortcomings of the current environmental risk assessment for fungicides.

Environmental Science & Technology↗
USGS2019

Assessing the lead solubility potential of untreated groundwater of the United States

In the U.S., about 44 million people rely on self-supplied groundwater for drinking water. Because most self-supplied homeowners do not treat their water to control corrosion, drinking water can be susceptible to lead (Pb) contamination from metal plumbing. To assess the types and locations of susceptible groundwater, a geochemical reaction model that included pure Pb minerals and solid solutions of calcite (Ca x Pb 1– x CO 3 ) and apatite [Ca x Pb 5-x (PO 4 ) 3 (OH; Cl; F)] was developed to estimate the lead solubility potential (LSP) for over 8300 untreated groundwater samples collected from domestic and public-supply sites between 2000 and 2016 in the U.S. The LSP is the calculated amount of Pb metal that could dissolve at 25 °C before a Pb-bearing mineral precipitates. About 33% of untreated groundwater samples had LSP greater than 15 μg/L—the USEPA action level for dissolved plus particulate forms of Pb. Five percent of samples had high LSP (above 300 μg/L) and tended to occur in the eastern and southeastern U.S. Measured Pb concentrations above 15 μg/L were rarely detected (<1%) but always coincided with high LSP values. Future work will provide a better understanding of the relation between water chemistry, Pb-mineral formation, and dissolved Pb concentrations in tap water.

Environmental Science & Technology↗
USGS2018

Reconnaissance of mixed organic and inorganic chemicals in private and public supply tapwaters at selected residential and workplace sites in the United States

Safe drinking water at the point-of-use (tapwater, TW) is a United States public health priority. Multiple lines of evidence were used to evaluate potential human health concerns of 482 organics and 19 inorganics in TW from 13 (7 public supply, 6 private well self-supply) home and 12 (public supply) workplace locations in 11 states. Only uranium (61.9 μg L –1 , private well) exceeded a National Primary Drinking Water Regulation maximum contaminant level (MCL: 30 μg L –1 ). Lead was detected in 23 samples (MCL goal: zero). Seventy-five organics were detected at least once, with median detections of 5 and 17 compounds in self-supply and public supply samples, respectively (corresponding maxima: 12 and 29). Disinfection byproducts predominated in public supply samples, comprising 21% of all detected and 6 of the 10 most frequently detected. Chemicals designed to be bioactive (26 pesticides, 10 pharmaceuticals) comprised 48% of detected organics. Site-specific cumulative exposure–activity ratios (∑ EAR ) were calculated for the 36 detected organics with ToxCast data. Because these detections are fractional indicators of a largely uncharacterized contaminant space, ∑ EAR in excess of 0.001 and 0.01 in 74 and 26% of public supply samples, respectively, provide an argument for prioritized assessment of cumulative effects to vulnerable populations from trace-level TW exposures.

Environmental Science & Technology↗
USGS2019

Cryptosporidium incidence and surface water influence of groundwater supplying public water systems in Minnesota, USA

Regulations for public water systems (PWS) in the U.S. consider Cryptosporidium a microbial contaminant of surface water supplies. Ground- water is assumed free of Cryptosporidium unless surface water is entering supply wells. We determined the incidence of Cryptosporidium in PWS wells varying in surface water influence. Community and noncommunity PWS wells (n = 145) were sampled (n = 964) and analyzed for Cryptosporidium by qPCR and immunofluorescence assay (IFA). Surface water influence was assessed by stable isotopes and the expert judgment of hydrogeologists using site-specific data. Fifty-eight wells (40%) and 107 samples (11%) were Cryptosporidium- positive by qPCR, and of these samples 67 were positive by IFA. Cryptosporidium concentrations measured by qPCR and IFA were significantly correlated (p < 0.001). Cryptosporidium incidence was not associated with surface water influence as assessed by stable isotopes or expert judgment. We successfully sequenced 45 of the 107 positive samples to identify species, including C. parvum (41), C. andersoni (2), and C. hominis (2), and the predominant subtype was C. parvum IIa A17G2R1. Assuming USA regulations for surface water-supplied PWS were applicable to the study wells, wells positive for Cryptosporidium by IFA would likely be required to add treatment. Cryptosporidium is not uncommon in groundwater, even when surface water influence is absent.

Minnesota↗
USGS2019

Hormones and pharmaceuticals in groundwater used as a source of drinking water across the United States

This is the first large-scale, systematic assessment of hormone and pharmaceutical occurrence in groundwater used for drinking across the United States. Samples from 1091 sites in Principal Aquifers representing 60% of the volume pumped for drinking-water supply had final data for 21 hormones and 103 pharmaceuticals. At least one compound was detected at 5.9% of 844 sites representing the resource used for public supply across the entirety of 15 Principal Aquifers, and at 11.3% of 247 sites representing the resource used for domestic supply over subareas of nine Principal Aquifers. Of 34 compounds detected, one plastics component (bisphenol A), three pharmaceuticals (carbamazepine, sulfamethoxazole, and meprobamate), and the caffeine degradate 1,7-dimethylxanthine were detected in more than 0.5% of samples. Hydrocortisone had a concentration greater than a human-health benchmark at 1 site. Compounds with high solubility and low K oc were most likely to be detected. Detections were most common in shallow wells with a component of recent recharge, particularly in crystalline-rock and mixed land-use settings. Results indicate vulnerability of groundwater used for drinking water in the U.S. to contamination by these compounds is generally limited, and exposure to these compounds at detected concentrations is unlikely to have adverse effects on human health.

Environmental Science & Technology↗
USGS2019

Integrated assessment of wastewater reuse, exposure risk, and fish endocrine disruption in the Shenandoah River watershed

Reuse of municipal and industrial wastewater treatment plant (WWTP) effluent is an important component in augmenting global freshwater supplies. The Shenandoah River Watershed was selected to conduct on-site exposure experiments to assess endocrine disrupting characteristics of different source waters. This investigation of the Shenandoah River Watershed integrates WWTP wastewater reuse modeling, hydrological and chemical characterization, and in vivo endocrine disruption bioassessment to assess contaminant sources, exposure pathways, and biological effects. The percentage of accumulated WWTP effluent in each river reach (ACCWW) was used to predict environmental concentrations for consumer product chemicals (boron), pharmaceutical compounds (carbamazepine), and steroidal estrogens (estrone, 17-beta-estradiol, estriol, and 17-alpha-ethinylestradiol). Fish endocrine disruption was evaluated using vitellogenin induction in male or juvenile fathead minnows. Water samples were analyzed for >500 inorganic and organic constituents to characterize the complex contaminant mixtures. Municipal ACCWW at drinking water treatment plant surface-water intakes ranged from <0.01 to 2.1 % under mean-annual streamflow and up to 4.7 % under August streamflow. Measured and predicted environmental concentrations resulted in 17-beta-estradiol equivalency quotients ranging from <0.05 to 5.1 ng L-1 indicating low-to-moderate risk of fish endocrine disruption. Results from the fish exposure experiments also showed limited estrogenic effects as indicated by the low (0.5- to 3.2-fold) vitellogenin induction.

Shenandoah River watershed↗
USGS2019

Geochemical factors controlling dissolved elemental mercury and methylmercury formation in Alaskan wetlands of varying trophic status

Transformations of aqueous inorganic divalent mercury (Hg(II)i) to volatile dissolved gaseous mercury (Hg(0)(aq)) and toxic methylmercury (MeHg) governs mercury bioavailability and fate in northern ecosystems. This study quantified concentrations of aqueous mercury species (Hg(II)i, Hg(0)(aq), MeHg) and relevant geochemical constituents in pore waters of eight Alaskan wetlands that differ in trophic status (i.e., bog-to-fen gradient) to gain insight on processes controlling dark Hg(II)i reduction and Hg(II)i methylation. Regardless of wetland trophic status, positive correlations were observed between pore water Hg(II)i and dissolved organic carbon (DOC) concentrations. The concentration ratio of Hg(0)(aq) to Hg(II)i exhibited an inverse relationship to Hg(II)i concentration. A ubiquitous pathway for Hg(0)(aq) formation was not identified based on geochemical data, but we surmise that dissolved organic matter (DOM) influences mercury retention in wetland pore waters by complexing Hg(II)i and decreasing the concentration of volatile Hg(0)(aq) relative to Hg(II)i. There was no evidence of Hg(0)(aq) abundance directly limiting mercury methylation. The concentration of MeHg relative to Hg(II)i was greatest in wetlands of intermediate trophic status, and geochemical data suggest mercury methylation pathways vary between wetlands. Our insights on geochemical factors influencing aqueous mercury speciation should be considered in context of the long-term fate of mercury in northern wetlands.

Environmental Science & Technology↗
USGS2019

Toxicokinetics of imidacloprid-coated wheat seeds in Japanese quail (Coturnix japonica) and an evaluation of hazard

Birds are potentially exposed to neonicotinoid insecticides by ingestion of coated seeds during crop planting. Adult male Japanese quail were orally dosed with wheat seeds coated with an imidacloprid (IMI) formulation at either 0.9 mg/kg body weight (BW) or 2.7 mg/kg BW (~3 and 9% of IMI LD50 for Japanese quail, respectively) for 1 or 10 days. Quail were euthanized between 1 and 24 h post-exposure to assess toxicokinetics. Analysis revealed rapid absorption (1 h) into blood, and distribution to brain, muscle, kidney and liver. Clearance to below detection limits occurred at both dose levels and exposure durations in all tissues within 24 h. Metabolism was extensive, with 5-OH-IMI and IMI-olefin detected at greater concentrations than IMI in tissues and fecal samples. There was no lethality or overt signs of toxicity at either dose level. Furthermore, no evidence of enhanced expression of mRNA genes associated with hepatic xenobiotic metabolism, oxidative DNA damage or alterations in concentrations of corticosterone and thyroid hormones was observed. Application of the toxicokinetic data was used to predict IMI residue levels in liver with reasonable results for some field exposure and avian mortality events. It would appear that some affected species are either consuming larger quantities of seeds or exhibit differences in ADME or sensitivity than predicted by read-across from these data.

Environmental Science & Technology↗
USGS2019

Mercury exposure and altered parental nesting behavior in a wild songbird

Methylmercury is a neurotoxin and endocrine disruptor and may impair avian reproduction directly through embryotoxicity or by altering parental care behaviors. We studied mercury exposure and incubation behavior of free-living tree swallows (Tachycineta bicolor) nesting in artificial nest boxes. Using small temperature dataloggers, we measured incubation constancy (the proportion of each day the female spent incubating eggs), the number of incubation recesses taken per day, and the duration of incubation recesses. We also assessed maternal mercury exposure by measuring mercury concentrations in both blood and eggs. Females with higher mercury concentrations exhibited lower incubation constancy, took more frequent and shorter incubation recesses, and were more likely to take incubation recesses that caused nest temperature decreases that were likely to slow embryonic development. Overall, females that laid eggs with the highest observed mercury concentration (0.53 μg/g fww) spent an average of 12% less time incubating their eggs over the 14-day incubation period than females that laid eggs with the lowest mercury concentration (0.07 μg/g fww). Because less time spent incubating can lower egg temperatures, slow embryonic development, and potentially lengthen the incubation period, these results suggest that environmentally relevant mercury concentrations may negatively influence reproduction by altering parental nesting behaviors of wild songbirds

Environmental Science & Technology↗
USGS2019

Kinetic study on clogging of a geothermal pumping well triggered by mixing-induced biogeochemical reactions

The sustainability of ground-source geothermal systems can be severely impacted by microbially mediated clogging processes. Biofouling of water wells by hydrous ferric oxide is a widespread problem. Although the mechanisms and critical environmental factors associated with clogging development are widely recognized, effects of mixing processes within the wells and time scales for clogging processes are not well characterized. Here we report insights from a joint hydrological, geochemical, and metagenomics characterization of a geothermal doublet in which hydrous ferric oxide and hydrous manganese oxide deposits had formed as a consequence of mixing shallow groundwater containing dissolved oxygen and nitrate with deeper, anoxic groundwater containing dissolved iron (Fe II ) and manganese (Mn II ). Metagenomics identify distinct bacteria consortia in the pumping well oxic and anoxic zones, including autotrophic iron-oxidizing bacteria. Batch mixing experiments and geochemical kinetics modeling of the associated reactions indicate that Fe II and Mn II oxidation are slow compared to the residence time of water in the pumping well; however, adsorption of Fe II and Mn II by accumulated hydrous ferric oxide and hydrous manganese oxide in the well bore and pump riser provides “infinite” time for surface-catalyzed oxidation and a convenient source of energy for iron-oxidizing bacteria, which colonize the surfaces and also catalyze oxidation. Thus, rapid clogging is caused by mixing-induced redox reactions and is exacerbated by microbial activity on accumulated hydrous oxide surfaces.

Orleans↗
USGS2019

Hydrocarbons in upland groundwater, Marcellus Shale Region, Northeastern Pennsylvania and Southern New York, USA

Water samples from 50 domestic wells located <1 km (proximal) and >1 km (distal) from shale-gas wells in upland areas of the Marcellus Shale region were analyzed for chemical, isotopic, and groundwater-age tracers. Uplands were targeted because natural mixing with brine and hydrocarbons from deep formations is less common in those areas compared to valleys. CH 4 -isotope, predrill CH 4 -concentration, and other data indicate that one proximal sample (5% of proximal samples) contains thermogenic CH 4 (2.6 mg/L) from a relatively shallow source (Catskill/Lock Haven Formations) that appears to have been mobilized by shale-gas production activities. Another proximal sample contains five other volatile hydrocarbons (0.03–0.4 μg/L), including benzene, more hydrocarbons than in any other sample. Modeled groundwater-age distributions, calibrated to 3 H, SF 6 , and 14 C concentrations, indicate that water in that sample recharged prior to shale-gas development, suggesting that land-surface releases associated with shale-gas production were not the source of those hydrocarbons, although subsurface leakage from a nearby gas well directly into the groundwater cannot be ruled out. Age distributions in the samples span ∼20 to >10000 years and have implications for relating occurrences of hydrocarbons in groundwater to land-surface releases associated with recent shale-gas production and for the time required to flush contaminants from the system.

New York, Pennsylvania↗
USGS2019

Occurrence and sources of radium in groundwater associated with oil fields in the southern San Joaquin Valley, California

Geochemical data from 40 water wells were used to examine the occurrence and sources of radium (Ra) in groundwater associated with three oil fields in California (Fruitvale, Lost Hills, South Belridge). 226Ra+228Ra activities (range=0.010-0.51 Bq/L) exceeded the 0.185 Bq/L drinking-water standard in 18% of the wells (not drinking-water wells). Radium activities were correlated with TDS concentrations (p<0.001, ρ=0.90, range=145-15,900 mg/L), Mn+Fe concentrations (p<0.001, ρ=0.82, range=<0.005-18.5 mg/L), and pH (p<0.001, ρ=-0.67, range=6.2-9.2), indicating Ra in groundwater was influenced by salinity, redox, and pH. Ra-rich groundwater was mixed with up to 45% oil-field water at some locations, primarily infiltrating through unlined disposal ponds, based on Cl, Li, noble-gas, and other data. Yet 228Ra/226Ra ratios in pond-impacted groundwater (median=3.1) differed from those in oil-field water (median=0.51). PHREEQC mixing calculations and spatial geochemical variations suggest the Ra in oil-field water was removed by co-precipitation with secondary barite and adsorption on Mn-Fe precipitates in the near-pond environment. The saline, organic-rich oil-field water subsequently mobilized Ra from downgradient aquifer sediments via Ra-desorption and Mn/Fe-reduction processes. This study demonstrates that infiltration of oil-field water may leach Ra into groundwater by changing salinity and redox conditions in the subsurface rather than by mixing with a high-Ra source.

California↗
USGS2019

Cell-Based metabolomics for untargeted screening and prioritization of vertebrate-active stressors in streams across the United States

The U.S. Geological Survey and the U.S. Environmental Protection Agency have assessed contaminants in 38 streams across the U.S., using an extensive suite of target-chemical analysis methods along with a variety of biological effects tools. Here we report zebrafish liver (ZFL) cell-culture based NMR metabolomic analysis of these split stream samples. We used this untargeted approach to evaluate the sites according to overall impact on the ZFL metabolome and found that neither the total number of organics detected at the sites, nor their cumulative concentrations, were good predictors of these impacts. Further, we used partial-least squares regression to compare ZFL endogenous metabolite profiles to values for 455 potential stressors (organics, inorganics, and physical properties) measured in these waters and found that the profiles covaried with at most 280 of the stressors, which were subsequently ranked into quartiles based on the strength of their covariance. While contaminants of emerging concern (CECs) were well represented in the top, most strongly, covarying quartile – suggesting considerable potential for eliciting biological responses at these sites – there was even higher representation of various well-characterized legacy contaminants (e.g., PCBs). These results emphasize the importance of complementing chemical analysis with untargeted bioassays to help focus regulatory efforts on the most significant ecosystem threats.

Environmental Science & Technology↗