Potential Toxicity of Dissolved Metal Mixtures (Cd, Cu, Pb, Zn) to Early Life Stage White Sturgeon ( Acipenser transmontanus) in the Upper Columbia River, Washington, United States.

The Upper Columbia River (UCR) received historical releases of smelter waste resulting in elevated metal concentrations in downstream sediments. Newly hatched white sturgeon hide within the rocky substrate at the sediment-water interface in the UCR for a few weeks before swim-up. Hiding behavior could expose them to metal contaminants, and metal toxicity could contribute to population declines in white sturgeon over the past 50 years. This study evaluates whether there is a link between the toxicity of dissolved metals across the sediment-water interface in the UCR and the survival of early life stage (ELS) white sturgeon. Toxicity of dissolved metal mixtures is evaluated using a combination of previously collected laboratory and field data and recently developed metal mixture toxicity models. The laboratory data consist of individual metal (Cd, Cu, Pb, and Zn) toxicity studies with ELS white sturgeon. The field data include the chemical composition of surface and pore water samples that were collected across the sediment-water interface in the UCR. These data are used in three metal accumulation and two response models. All models predict low toxicity in surface water, whereas effects concentrations greater than 20% are predicted for 60-72% of shallow pore water samples. The flux of dissolved metals, particularly Cu, from shallow pore water to surface water likely exposes prime ELS sturgeon habitat to toxic conditions.

Evaluation of a combined macrophyte-epiphyte bioassay for assessing nutrient enrichment in the Portneuf River, Idaho, USA.

We describe and evaluate a laboratory bioassay that uses Lemna minor L. and attached epiphytes to characterize the status of ambient and nutrient-enriched water from the Portneuf River, Idaho. Specifically, we measured morphological (number of fronds, longest surface axis, and root length) and population-level (number of plants and dry mass) responses of L. minor and community-level (ash-free dry mass [AFDM] and chlorophyll a [Chl a]) responses of epiphytes to nutrient enrichment. Overall, measures of macrophyte biomass and abundance increased with increasing concentrations of dissolved phosphorus (P) and responded more predictably to nutrient enrichment than morphological measures. Epiphyte AFDM and Chl a were also greatest in P-enriched water; enrichments of N alone produced no measurable epiphytic response. The epiphyte biomass response did not directly mirror macrophyte biomass responses, illustrating the value of a combined macrophyte-epiphyte assay to more fully evaluate nutrient management strategies. Finally, the most P-enriched waters not only supported greater standing stocks of macrophyte and epiphytes but also had significantly higher water column dissolved oxygen and dissolved organic carbon concentrations and a lower pH. Advantages of this macrophyte-epiphyte bioassay over more traditional single-species assays include the use of a more realistic level of biological organization, a relatively short assay schedule (~10 days), and the inclusion of multiple biological response and water-quality measures.

Bioavailability and Toxicity Models of Copper to Freshwater Life: The State of Regulatory Science.

Efforts to incorporate bioavailability adjustments into regulatory water quality criteria in the United States have included four major procedures: hardness-based single-linear regression equations, water-effect ratios (WERs), biotic ligand models (BLMs), and multiple-linear regression models (MLRs) that use dissolved organic carbon, hardness, and pH. The performance of each with copper (Cu) is evaluated, emphasizing the relative performance of hardness-based versus MLR-based criteria equations. The WER approach was shown to be inherently highly biased. The hardness-based model is in widest use, and the MLR approach is the US Environmental Protection Agency's (USEPA's) present recommended approach for developing aquatic life criteria for metals. The performance of criteria versions was evaluated with numerous toxicity datasets that were independent of those used to develop the MLR models, including olfactory and behavioral toxicity, and field and ecosystem studies. Within the range of water conditions used to develop the Cu MLR criteria equations, the MLR performed well in terms of predicting toxicity and protecting sensitive species and ecosystems. In soft waters, the MLR outperformed both the BLM and hardness models. In atypical waters with pH <5.5 or >9, neither the MLR nor BLM predictions were reliable, suggesting that site-specific testing would be needed to determine reliable Cu criteria for such settings. The hardness-based criteria performed poorly with all toxicity datasets, showing no or weak ability to predict observed toxicity. In natural waters, MLR and BLM criteria versions were strongly correlated. In contrast, the hardness-criteria version was often out of phase with the MLR and, depending on waterbody and season, could be either strongly overprotective or underprotective. The MLR-based USEPA-style chronic criterion appears to be more generally protective of ecosystems than other models. Environ Toxicol Chem 2023;42:2529-2563. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

The Capacity of Freshwater Ecosystems to Recover from Exceedences of Aquatic Life Criteria.

In the United States, national chemical water quality criteria for the protection of aquatic life assume that aquatic ecosystems have sufficient resiliency to recover from criteria exceedences occurring up to once every 3 years. This resiliency assumption was critically reviewed through two approaches: (1) synthesis of case studies, and (2) population modeling. The population modeling examined differences in recovery of species with widely different life histories. One invertebrate (Hyalella azteca) and four fish species were modeled (fathead minnow, brook trout, lake trout, and shortnose sturgeon) with various disturbance magnitudes and intervals. The synthesis of ecosystem case studies showed generally faster recoveries for insect communities rather than fish, and recoveries from pulse (acute) disturbances were often faster than recoveries from press (chronic) disturbances. When the recovery dataset excluded severe disturbances that seemed unrepresentative of common facility discharge upsets that might cause criteria exceedences, the median recovery time was 1 year, 81% of the cases were considered recovered within 3 years, and 95% were considered recovered within 10 years. The modeling projected that short-lived fish species with high recovery times could thrive despite enduring 50% mortality disturbances every other year. However, long-lived fish species had longer recovery times and declined under the one disturbance every 3 years scenario. Overall, the analyses did not refute the long-standing judgements that 3 years is generally sufficient for recovery from nonrepetitive, moderate intensity disturbances of a magnitude up to 2× the chronic criteria in waters without other pollution sources or stresses. However, these constraints may not always be met and if long-lived fish species are a concern, longer return intervals such as 5-10 years could be indicated. Environ Toxicol Chem 2022;41:2887-2910. Published 2022. This article is a U.S. Government work and is in the public domain in the USA.

Nutrient limitation of algae and macrophytes in streams: Integrating laboratory bioassays, field experiments, and field data.

Successful eutrophication control strategies need to address the limiting nutrient. We conducted a battery of laboratory and in situ nutrient-limitation tests with waters collected from 9 streams in an agricultural region of the upper Snake River basin, Idaho, USA. Laboratory tests used the green alga Raphidocelis subcapitata, the macrophyte Lemna minor (duckweed) with native epiphytes, and in situ nutrient-limitation tests of periphyton were conducted with nutrient-diffusing substrates (NDS). In the duckweed/epiphyte test, P saturation occurred when concentrations reached about 100 µg/L. Chlorophyll a in epiphytic periphyton was stimulated at low P additions and by about 100 µg/L P, epiphytic periphyton chlorophyll a appeared to be P saturated. Both duckweed and epiphyte response patterns with total N were weaker but suggested a growth stimulation threshold for duckweed when total N concentrations exceeded about 300 µg/L and approached saturation at the highest N concentration tested, 1300 µg/L. Nutrient uptake by epiphytes and macrophytes removed up to 70 and 90% of the N and P, respectively. The green algae and the NDS nutrient-limitation test results were mostly congruent; N and P co-limitation was the most frequent result for both test series. Across all tests, when N:P molar ratios >30 (mass ratios >14), algae or macrophyte growth was P limited; N limitation was observed at N:P molar ratios up to 23 (mass ratios up to 10). A comparison of ambient periphyton chlorophyll a concentrations with chlorophyll a accrued on control artificial substrates in N-limited streams, suggests that total N concentrations associated with a periphyton chlorophyll a benchmark for desirable or undesirable conditions for recreation would be about 600 to 1000 µg/L total N, respectively. For P-limited streams, the corresponding benchmark concentrations were about 50 to 90 µg/L total P, respectively. Our approach of integrating controlled experiments and matched biomonitoring field surveys was cost effective and more informative than either approach alone.

Direct and Delayed Mortality of Ceriodaphnia dubia and Rainbow Trout Following Time-Varying Acute Exposures to Zinc.

The potential for delayed mortality following short-term episodic pollution events was evaluated by exposing cladocerans (Ceriodaphnia dubia) and rainbow trout (Oncorhynchus mykiss) to zinc (Zn) in various 1- to 48-h and 1- to 96-h exposures, respectively, followed by transferring the exposed organisms to clean water for up to 47 h for C. dubia and up to 95 h for trout for additional observation. For C. dubia, 1-h exposures of up to 3790 µg Zn/L never resulted in mortality during the actual Zn exposures, but by 48 h, a 1-h exposure to 114 µg/L, a concentration similar to the present US national water quality acute criterion for the test water conditions, ultimately killed 70% of C. dubia. With C. dubia, the speed of action of Zn toxicity was faster for intermediate concentrations than for the highest concentrations tested. For rainbow trout, pronounced delayed mortalities by 96 h only occurred following ≥8-h exposures. For both species, ultimate mortalities from Zn exposures ≤8 h mostly presented as delayed mortalities, whereas for exposures ≥24 h, almost all ultimate mortalities presented during the actual exposure periods. With Zn, risks of delayed mortality following exposures to all concentrations tested were much greater for the more sensitive, small-bodied invertebrate (C. dubia) than for the less sensitive, larger-bodied fish (rainbow trout). These results, along with previous studies, show that delayed mortality is an important consideration in evaluating risks to aquatic organisms from brief, episodic exposures to some substances. Environ Toxicol Chem 2021;40:2484-2498. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Relevance of risk predictions derived from a chronic species sensitivity distribution with cadmium to aquatic populations and ecosystems.

Criteria to protect aquatic life are intended to protect diverse ecosystems, but in practice are usually developed from compilations of single-species toxicity tests using standard test organisms that were tested in laboratory environments. Species sensitivity distributions (SSDs) developed from these compilations are extrapolated to set aquatic ecosystem criteria. The protectiveness of the approach was critically reviewed with a chronic SSD for cadmium comprising 27 species within 21 genera. Within the data set, one genus had lower cadmium effects concentrations than the SSD fifth percentile-based criterion, so in theory this genus, the amphipod Hyalella, could be lost or at least allowed some level of harm by this criteria approach. However, population matrix modeling projected only slightly increased extinction risks for a temperate Hyalella population under scenarios similar to the SSD fifth percentile criterion. The criterion value was further compared to cadmium effects concentrations in ecosystem experiments and field studies. Generally, few adverse effects were inferred from ecosystem experiments at concentrations less than the SSD fifth percentile criterion. Exceptions were behavioral impairments in simplified food web studies. No adverse effects were apparent in field studies under conditions that seldom exceeded the criterion. At concentrations greater than the SSD fifth percentile, the magnitudes of adverse effects in the field studies were roughly proportional to the laboratory-based fraction of species with adverse effects in the SSD. Overall, the modeling and field validation comparisons of the chronic criterion values generally supported the relevance and protectiveness of the SSD fifth percentile approach with cadmium.

Copper Concentrations in the Upper Columbia River as a Limiting Factor in White Sturgeon Recruitment and Recovery.

Currently there is little natural recruitment of white sturgeon (Acipenser transmontanus) in the Upper Columbia River located in British Columbia, Canada and Washington, USA. This review of life history, physiology, and behavior of white sturgeon, along with data from recent toxicological studies, suggest that trace metals, especially Cu, affect survival and behavior of early life stage fish. Sturgeon free embryos, first feeding embryos, and mixed feeding embryos utilize interstitial spaces between gravel. Although concentrations of Cu in the water column of the Upper Columbia River are typically less than US water quality criteria defined to protect aquatic life, samples at the sediment-water interface were as large as 24 µg/L and exceed the criteria. Toxicological studies reviewed here demonstrate mortality, loss of equilibrium, and immobility at Cu concentrations of 1.5 to <16 µg/L and reduced swimming activity was documented at 0.88 to 7 µg/L. Contaminated invertebrates and slag particles provide other routes of exposure. These additional routes of exposure can cause indirect effects from starvation due to potential lack of prey items and ingestion of contaminated prey or slag particles. The lack of food in stomachs during these critical early life stages may coincide with a threshold "point of no return" at which sturgeon will be unable to survive even if food becomes available following that early time frame. These findings become especially important as work progresses to enhance white sturgeon recruitment in the Upper Columbia River. To date, decisions against including trace metals as a factor in sturgeon recovery have focused on surface-water concentrations and measurements of lethality (LC50) to establish threshold concentrations for sturgeon sensitivity. However, information provided here suggests that measurements from the sediment-water interface and effect concentrations (EC50) be considered with white sturgeon life history characteristics. These data support minimizing Cu exposure risk to enhance a successful white sturgeon recovery effort. Integr Environ Assess Manag 2020;16:378-391. Published 2020. This article is a US Government work and is in the public domain inthe USA.

Time-dependent accumulation of Cd, Co, Cu, Ni, and Zn in natural communities of mayfly and caddisfly larvae: Metal sensitivity, uptake pathways, and mixture toxicity.

Conceptual and quantitative models were developed to assess time-dependent processes in four sequential experimental stream studies that determined abundances of natural communities of mayfly and caddisfly larvae dosed with single metals (Cd, Co, Cu, Ni, Zn) or multiple metals (Cd + Zn, Co + Cu, Cu + Ni, Cu + Zn, Ni + Zn, Cd + Cu + Zn, Co + Cu + Ni, Cu + Ni + Zn). Metal mixtures contained environmentally relevant metal ratios found in mine drainage. Free metal ion concentrations, accumulation of metals by periphyton, and metal uptake by four families of aquatic insect larvae were either measured (Brachycentridae) or predicted (Ephemerellidae, Heptageniidae, Hydropsychidae) using equilibrium and biodynamic models. Toxicity functions, which included metal accumulations by larvae and metal potencies, were linked to abundances of the insect families. Model results indicated that mayflies accumulated more metal than caddisflies and the relative importance of metal uptake by larvae via dissolved or dietary pathways highly depended on metal uptake rate constants for each insect family and concentrations of metals in food and water. For solution compositions in the experimental streams, accumulations of Cd, Cu, and Zn in larvae occurred primarily through dietary uptake, whereas uptake of dissolved metal was more important for Co and Ni accumulations. Cd, Cu, and Ni were major contributors to toxicity in metal mixtures and for metal ratios examined. Our conceptual approach and quantitative results should aid in designing laboratory experiments and field studies that evaluate metal uptake pathways and metal mixture toxicity to aquatic biota.

Bioaccumulation and Toxicity of Cadmium, Copper, Nickel, and Zinc and Their Mixtures to Aquatic Insect Communities.

We describe 2 artificial stream experiments that exposed aquatic insect communities to zinc (Zn), copper (Cu), and cadmium (year 2014) and to Zn, Cu, and nickel (year 2015). The testing strategy was to concurrently expose insect communities to single metals and mixtures. Single-metal tests were repeated to evaluate the reproducibility of the methods and year-to-year variability. Metals were strongly accumulated in sediments, periphyton, and insect (caddisfly) tissues, with the highest concentrations occurring in periphyton. Sensitive mayflies declined in metal treatments, and effect concentrations could be predicted effectively from metal concentrations in either periphyton or water. Most responses were similar in the replicated tests, but median effect concentration values for the mayfly Rhithrogena sp. varied 20-fold between the tests, emphasizing the difficulty comparing sensitivities across studies and the value of repeated testing. Relative to the single-metal responses, the toxicity of the mixtures was either approximately additive or less than additive when calculated as the product of individual responses (response addition). However, even less-than-additive relative responses were sometimes greater than responses to similar concentrations tested singly. The ternary mixtures resulted in mayfly declines at concentrations that caused no declines in the concurrent single-metal tests. When updating species-sensitivity distributions (SSDs) with these results, the mayfly responses were among the most sensitive 10th percentile of available data for all 4 metals, refuting older literature placing mayflies in the insensitive portion of metal SSDs. Testing translocated aquatic insect communities in 30-d artificial streams is an efficient approach to generate multiple species effect values under quasi-natural conditions that are relevant to natural streams. Environ Toxicol Chem 2020;39:812-833. Published 2020 Wiley Periodicals, Inc. on behalf of SETAC. This article is a US government work, and as such, is in the public domain in the United States of America.

Metal Bioavailability Models: Current Status, Lessons Learned, Considerations for Regulatory Use, and the Path Forward.

Since the early 2000s, biotic ligand models and related constructs have been a dominant paradigm for risk assessment of aqueous metals in the environment. We critically review 1) the evidence for the mechanistic approach underlying metal bioavailability models; 2) considerations for the use and refinement of bioavailability-based toxicity models; 3) considerations for the incorporation of metal bioavailability models into environmental quality standards; and 4) some consensus recommendations for developing or applying metal bioavailability models. We note that models developed to date have been particularly challenged to accurately incorporate pH effects because they are unique with multiple possible mechanisms. As such, we doubt it is ever appropriate to lump algae/plant and animal bioavailability models; however, it is often reasonable to lump bioavailability models for animals, although aquatic insects may be an exception. Other recommendations include that data generated for model development should consider equilibrium conditions in exposure designs, including food items in combined waterborne-dietary matched chronic exposures. Some potentially important toxicity-modifying factors are currently not represented in bioavailability models and have received insufficient attention in toxicity testing. Temperature is probably of foremost importance; phosphate is likely important in plant and algae models. Acclimation may result in predictions that err on the side of protection. Striking a balance between comprehensive, mechanistically sound models and simplified approaches is a challenge. If empirical bioavailability tools such as multiple-linear regression models and look-up tables are employed in criteria, they should always be informed qualitatively and quantitatively by mechanistic models. If bioavailability models are to be used in environmental regulation, ongoing support and availability for use of the models in the public domain are essential. Environ Toxicol Chem 2019;39:60-84. © 2019 SETAC.

Evaluation of acute copper toxicity to juvenile freshwater mussels (fatmucket, Lampsilis siliquoidea) in natural and reconstituted waters.

The influence of dissolved organic carbon (DOC) and water composition on the toxicity of copper to juvenile freshwater mussels (fatmucket, Lampsilis siliquoidea) were evaluated in natural and reconstituted waters. Acute 96-h copper toxicity tests werec onducted at four nominal DOC concentrations (0, 2.5, 5, and 10 mg/L as carbon [C]) in dilutions of natural waters and in American Society for Testing and Materials (ASTM) reconstituted hard water. Toxicity tests also were conducted in ASTM soft, moderately hard, hard, and very hard reconstituted waters (nominal hardness 45-300 mg/L as CaCO3). Three natural surface waters (9.5-11 mg/L DOC) were diluted to obtain a series of DOC concentrations with diluted well water, and an extract of natural organic matter and commercial humic acid was mixed with ASTM hard water to prepare a series of DOC concentrations for toxicity testing. Median effective concentrations (EC50s) for dissolved copper varied >40-fold (9.9 to >396 gg Cu/L) over all 21 treatments in various DOC waters. Within a particular type of DOC water, EC50s increased 5- to 12-fold across DOC concentrations of 0.3 to up to 11 mg C/L. However, EC50s increased by only a factor of 1.4 (21-30 gg Cu/L) in the four ASTM waters with wide range of water hardness (52-300 mg CaCO3/L). Predictions from the biotic ligand model (BLM) for copper explained nearly 90% of the variability in EC50s. Nearly 70% of BLM-normalized EC50s for fatmucket tested in natural waters were below the final acute value used to derive the U.S. Environmental Protection Agency acute water quality criterion for copper, indicating that the criterion might not be protective of fatmucket and perhaps other mussel species.

Scientific integrity issues in Environmental Toxicology and Chemistry: Improving research reproducibility, credibility, and transparency.

High-profile reports of detrimental scientific practices leading to retractions in the scientific literature contribute to lack of trust in scientific experts. Although the bulk of these have been in the literature of other disciplines, environmental toxicology and chemistry are not free from problems. While we believe that egregious misconduct such as fraud, fabrication of data, or plagiarism is rare, scientific integrity is much broader than the absence of misconduct. We are more concerned with more commonly encountered and nuanced issues such as poor reliability and bias. We review a range of topics including conflicts of interests, competing interests, some particularly challenging situations, reproducibility, bias, and other attributes of ecotoxicological studies that enhance or detract from scientific credibility. Our vision of scientific integrity encourages a self-correcting culture that promotes scientific rigor, relevant reproducible research, transparency in competing interests, methods and results, and education. Integr Environ Assess Manag 2019;00:000-000. © 2019 SETAC.

Understanding the captivity effect on invertebrate communities transplanted into an experimental stream laboratory.

Little is known about how design and testing methodologies affect the macroinvertebrate communities that are held captive in mesocosms. To address this knowledge gap, we conducted a 32-d test to determine how seeded invertebrate communities changed once removed from the natural stream and introduced to the laboratory. We evaluated larvae survival and adult emergence in controls from 4 subsequent studies, as well as corresponding within-river community changes. The experimental streams maintained about 80% of the invertebrates that originally colonized the introduced substrates. Many macroinvertebrate populations experienced changes in numbers through time, suggesting that these taxa are unlikely to maintain static populations throughout studies. For example, some taxa (Tanytarsini, Simuliidae, Cinygmula sp.) increased in number, grew (Simuliidae), and possibly recruited new individuals (Baetidae) as larvae, while several also completed other life history events (pupation and emergence) during the 30- to 32-d studies. Midges and mayflies dominated emergence, further supporting the idea that conditions are conducive for many taxa to complete their life cycles while held captive in the experimental streams. However, plecopterans were sensitive to temperature changes >2 °C between river and laboratory. Thus, this experimental stream testing approach can support diverse larval macroinvertebrate communities for durations consistent with some chronic criterion development and life cycle assessments (i.e., 30 d). The changes in communities held captive in the experimental streams were mostly consistent with the parallel changes observed from in situ river samples, indicating that mesocosm results are reasonably representative of real river insect communities. Environ Toxicol Chem 2018;37:2820-2834. Published 2018 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

Characterizing toxicity of metal-contaminated sediments from the Upper Columbia River, Washington, USA, to benthic invertebrates.

Sediments from the Upper Columbia River, Washington, USA, are contaminated with metals from smelting operations. We conducted short-term and long-term tests with the midge Chironomus dilutus and the amphipod Hyalella azteca and short-term tests with the freshwater mussel Lampsilis siliquoidea with 54 sediments from the Upper Columbia River to characterize thresholds for toxicity of metals to benthic invertebrates. Test sediments were screened for toxicity by comparisons with low-metal reference sediments. Toxic effects on amphipods occurred primarily in sediments from the upstream (riverine) reach, and toxic effects on midges occurred in sediments from both the upstream reach and the downstream (reservoir) reach. Little toxicity was observed in mussel tests. Toxicity thresholds (20% effect concentrations [EC20s]) for metals in sediment and porewater were estimated from logistic concentration-response models. Copper (Cu) concentrations in the simultaneously extracted metal fraction of sediments and bioavailable Cu in porewater, as characterized by biotic ligand models, had consistent associations with toxicity endpoints. Concentration-response models for sediment Cu produced EC20s for 6 endpoints, with long-term amphipod survival and reproduction being the most sensitive. A logistic regression model fitted to an endpoint sensitivity distribution for sediment Cu predicted that approximately one-half of the sediments tested would be toxic to at least one endpoint and that approximately 20% of test sediments would be toxic to more than half of the endpoints. These results indicate that sediments from the upstream reach of the Upper Columbia River, which contain high concentrations of metals associated with slags, cause a wide range of toxic effects in laboratory tests and are likely to have adverse effects on benthic invertebrate communities. Environ Toxicol Chem 2018;37:3102-3114. Published 2018 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

An evaluation of freshwater mussel toxicity data in the derivation of water quality guidance and standards for copper.

The state of Oklahoma has designated several areas as freshwater mussel sanctuaries in an attempt to provide freshwater mussel species a degree of protection and to facilitate their reproduction. We evaluated the protection afforded freshwater mussels by the U.S. Environmental Protection Agency (U.S. EPA) hardness-based 1996 ambient copper water quality criteria, the 2007 U.S. EPA water quality criteria based on the biotic ligand model and the 2005 state of Oklahoma copper water quality standards. Both the criterion maximum concentration and criterion continuous concentration were evaluated. Published acute and chronic copper toxicity data that met American Society for Testing and Materials guidance for test acceptability were obtained for exposures conducted with glochidia or juvenile freshwater mussels. We tabulated toxicity data for glochidia and juveniles to calculate 20 species mean acute values for freshwater mussels. Generally, freshwater mussel species mean acute values were similar to those of the more sensitive species included in the U.S. EPA water quality derivation database. When added to the database of genus mean acute values used in deriving 1996 copper water quality criteria, 14 freshwater mussel genus mean acute values included 10 of the lowest 15 genus mean acute values, with three mussel species having the lowest values. Chronic exposure and sublethal effects freshwater mussel data available for four species and acute to chronic ratios were used to evaluate the criterion continuous concentration. On the basis of the freshwater mussel toxicity data used in this assessment, the hardness-based 1996 U.S. EPA water quality criteria, the 2005 Oklahoma water quality standards, and the 2007 U.S. EPA water quality criteria based on the biotic ligand model might need to be revised to afford protection to freshwater mussels.

Sensitivity of mottled sculpins (Cottus bairdi) and rainbow trout (Onchorhynchus mykiss) to acute and chronic toxicity of cadmium, copper, and zinc.

Studies of fish communities of streams draining mining areas suggest that sculpins (Cottus spp.) may be more sensitive than salmonids to adverse effects of metals. We compared the toxicity of zinc, copper, and cadmium to mottled sculpin (C. bairdi) and rainbow trout (Onchorhynchus mykiss) in laboratory toxicity tests. Acute (96-h) and early life-stage chronic (21- or 28-d) toxicity tests were conducted with rainbow trout and with mottled sculpins from populations in Minnesota and Missouri, USA, in diluted well water (hardness = 100 mg/L as CaCO3). Acute and chronic toxicity of metals to newly hatched and swim-up stages of mottled sculpins differed between the two source populations. Differences between populations were greatest for copper, with chronic toxicity values (ChV = geometric mean of lowest-observed-effect concentration and no-observed-effect concentration) of 4.4 microg/L for Missouri sculpins and 37 microg/L for Minnesota sculpins. Cadmium toxicity followed a similar trend, but differences between sculpin populations were less marked, with ChVs of 1.1 microg/L (Missouri) and 1.9 microg/L (Minnesota). Conversely, zinc was more toxic to Minnesota sculpins (ChV = 75 microg/L) than Missouri sculpins (chronic ChV = 219 microg/L). Species-average acute and chronic toxicity values for mottled sculpins were similar to or lower than those for rainbow trout and indicated that mottled sculpins were among the most sensitive aquatic species to toxicity of all three metals. Our results indicate that current acute and chronic water quality criteria for cadmium, copper, and zinc adequately protect rainbow trout but may not adequately protect some populations of mottled sculpins. Proposed water quality criteria for copper based on the biotic ligand model would be protective of both sculpin populations tested.

Larval aquatic insect responses to cadmium and zinc in experimental streams.

To evaluate the risks of metal mixture effects to natural stream communities under ecologically relevant conditions, the authors conducted 30-d tests with benthic macroinvertebrates exposed to cadmium (Cd) and zinc (Zn) in experimental streams. The simultaneous exposures were with Cd and Zn singly and with Cd+Zn mixtures at environmentally relevant ratios. The tests produced concentration-response patterns that for individual taxa were interpreted in the same manner as classic single-species toxicity tests and for community metrics such as taxa richness and mayfly (Ephemeroptera) abundance were interpreted in the same manner as with stream survey data. Effect concentrations from the experimental stream exposures were usually 2 to 3 orders of magnitude lower than those from classic single-species tests. Relative to a response addition model, which assumes that the joint toxicity of the mixtures can be predicted from the product of their responses to individual toxicants, the Cd+Zn mixtures generally showed slightly less than additive toxicity. The authors applied a modeling approach called Tox to explore the mixture toxicity results and to relate the experimental stream results to field data. The approach predicts the accumulation of toxicants (hydrogen, Cd, and Zn) on organisms using a 2-pKa bidentate model that defines interactions between dissolved cations and biological receptors (biotic ligands) and relates that accumulation through a logistic equation to biological response. The Tox modeling was able to predict Cd+Zn mixture responses from the single-metal exposures as well as responses from field data. The similarity of response patterns between the 30-d experimental stream tests and field data supports the environmental relevance of testing aquatic insects in experimental streams. Environ Toxicol Chem 2017;36:749-762. Published 2016 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

A long-term copper exposure in a freshwater ecosystem using lotic mesocosms: Invertebrate community responses.

A lotic mesocosm study was carried out in 20-m-long channels, under continuous, environmentally realistic concentrations of copper (Cu) in low, medium, and high exposures (nominally 0, 5, 25, and 75 µg L-1 ; average effective concentrations <0.5, 4, 20, and 57 µg L-1 respectively) for 18 mo. Total abundance, taxa richness, and community structure of zooplankton, macroinvertebrates, and emerging insects were severely affected at Cu treatment levels of 25 and 75 µg L-1 . Some taxa were sensitive to Cu, including gastropods such as Lymnaea spp. and Physa sp., crustaceans such as Chydorus sphaericus, Gammarus pulex, and Asellus aquaticus, rotifers such as Mytilina sp. and Trichocerca sp., leeches such as Erpobdella sp., and the emergence of dipteran insects such as Chironomini. Other taxa appeared to be tolerant or favored by indirect effects, as in Chironimidae larvae, the emergence of Orthocladiinae, and the zooplankter Vorticella sp., which increased in the 25 and 75 µg L-1 treatments. After approximately 8 mo of Cu exposure, the macroinvertebrate community in the high treatment was decimated to the point that few organisms could be detected, with moderate effects in the medium treatment, and very slight effects in the low-Cu treatment. Subsequently, most taxa in the high-Cu exposure began a gradual and partial recovery. By the end of the study at 18 mo, macroinvertebrate taxa richness was similar to control richness, although overall abundances remained lower than controls. After 18 mo of copper exposure, a no-observed-effect concentration at the community level for consumers was set at 5 µg L-1 (4 µg L-1 as average effective concentration), and a lowest-observed-effect concentration at 25 µg L-1 (20 µg L-1 as average effective concentration). Environ Toxicol Chem 2017;36:2698-2714. © 2017 SETAC.

Quantifying Fish Swimming Behavior in Response to Acute Exposure of Aqueous Copper Using Computer Assisted Video and Digital Image Analysis.

Behavioral responses of aquatic organisms to environmental contaminants can be precursors of other effects such as survival, growth, or reproduction. However, these responses may be subtle, and measurement can be challenging. Using juvenile white sturgeon (Acipenser transmontanus) with copper exposures, this paper illustrates techniques used for quantifying behavioral responses using computer assisted video and digital image analysis. In previous studies severe impairments in swimming behavior were observed among early life stage white sturgeon during acute and chronic exposures to copper. Sturgeon behavior was rapidly impaired and to the extent that survival in the field would be jeopardized, as fish would be swept downstream, or readily captured by predators. The objectives of this investigation were to illustrate protocols to quantify swimming activity during a series of acute copper exposures to determine time to effect during early lifestage development, and to understand the significance of these responses relative to survival of these vulnerable early lifestage fish. With mortality being on a time continuum, determining when copper first affects swimming ability helps us to understand the implications for population level effects. The techniques used are readily adaptable to experimental designs with other organisms and stressors.