The eastern oyster (Crassostrea virginica) supports a large aquaculture industry and is a keystone species along the Atlantic seaboard. Native oysters are routinely exposed to a complex mixture of contaminants that increasingly includes pharmaceuticals and personal care products (PPCPs). Unfortunately, the biological effects of chemical mixtures on oysters are poorly understood. Untargeted gas chromatography‐mass spectrometry metabolomics was utilized to quantify the response of oysters exposed to fluoxetine, N,N‐diethyl‐meta‐toluamide, 17α‐ethynylestradiol, diphenhydramine, and their mixture. Oysters were exposed to 1 µg/L of each chemical or mixture for 10 d, followed by an 8‐d depuration period. Adductor muscle (n = 14/treatment) was sampled at days 0, 1, 5, 10, and 18. Trajectory analysis illustrated that metabolic effects and class separation of the treatments varied at each time point and that, overall, the oysters were only able to partially recover from these exposures post‐depuration. Altered metabolites were associated with cellular energetics (i.e., Krebs cycle intermediates), as well as amino acid metabolism and fatty acids. Exposure to these PPCPs also affected metabolic pathways associated with anaerobic metabolism, osmotic stress, and oxidative stress, in addition to the physiological effects of each chemical's postulated mechanism of action. Following depuration, fewer metabolites were altered, but none of the treatments returned them to their initial control values, indicating that metabolic disruptions were long‐lasting. Interestingly, the mixture did not directly cluster with individual treatments in the scores plot from partial least squares discriminant analysis, and many of its affected metabolic pathways were not well predicted from the individual treatments. The present study highlights the utility of untargeted metabolomics in developing exposure biomarkers for compounds with different modes of action in bivalves. Environ Toxicol Chem 2020;00:1–18. © 2019 SETAC

Toxicity reference values for PFAS vary even when the same test organism is studied. While the need to confirm dosing solution concentrations is widely accepted, there are no experimental data to inform best practices when preparing PFAS solutions. Laboratory data indicate that dissolution time of PFAS solids cause statistically significant deviations between nominal and measured concentrations. Mixing times for select PFAS varied between 2‐5 hours, depending on carbon fluorine chain‐length.

Regulatory assessment of the bioaccumulation from water is commonly based on bioconcentration factors (BCFs) derived from fish flow‐through tests. Such experiments require many laboratory animals and are time‐consuming and costly. An alternative test setup for organic, neutral compounds using the amphipod Hyalella azteca was recently suggested, resulting in BCF values which show a strong correlation with fish BCF data. In the present study, the bioconcentration potential of the ionic compound laurate was elucidated in H. azteca. The sodium salt of 1‐14C laurate was applied to H. azteca in a flow‐through and a semistatic approach. Because of rapid biodegradation, a semistatic approach with frequent medium replacements was required to ensure a stable medium concentration. Laurate was also rapidly metabolized by H. azteca. A large proportion of the total radioactivity measured in the amphipod tissue was not extractable, suggesting that mineralized laurate was accumulated in the calcified exoskeleton of H. azteca. This was confirmed in a further study using carbonate [14C]. A lipid‐normalized (5.0%) Hyalella BCF of 8.9 was calculated for laurate, measured as free fatty acids. The results of the bioconcentration studies with H. azteca confirm the low bioaccumulation potential of the test item previously observed in fish. However, more organic ionic compounds with various properties need to be tested to assess whether a general correlation between fish and Hyalella BCF data exists. Environ Toxicol Chem 2020;00:1–13. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Low headspace oxygen was used in the hydroponic design to evaluate the toxicity of sulfide to wild rice (Zizania palustris). Oxygen levels in the headspace gas phase were maintained at <0.005 atm. Results from this study indicated that for the most sensitive endpoint (mesocotyl emergence), exposure of developing wild rice to sulfide at concentrations ≥3.1 mg/L sulfide was toxic based on assessment of NOEC and LOEC values in the presence of 0.8 mg/L Fe. However, exposure of developing wild rice to sulfide at concentrations ≥7.8 mg/L was necessary to significantly reduce emergence in the presence of 2.8 mg Fe/L based on the mesocotyl emergence, and shoot weight and length. Overall, mesocotyl emergence was consistently the most sensitive endpoint in the study, while seed activation, seedling survival, root growth, leaf number and biomass, and phytotoxicity were less sensitive endpoints. Results were similar to previous studies in which atmospheric oxygen was maintained in the headspace gas phase demonstrating that the concentration of oxygen in the headspace gas phase during mesocotyl emergence and early growth was not a significant factor in the sensitivity of wild rice to sulfide.

We report sublethal effects of environmentally relevant concentrations of chlorpyrifos (CPF) at the individual (swimming alterations) and biochemical level (esterases activities and antioxidant enzymes) in the Montevideo treefrog Boana pulchella larvae. The LC50‐96h for CPF in stage‐29 B. pulchella tadpoles was 0.98 mg/L and was close to the 65th‐percentile of published anuran species sensitivity. CPF disrupted biochemical processes in B. pulchella: tadpoles showed a significant inhibition of esterases activity and a significant induction of antioxidant enzymes, indicating a response to an environmental challenge causing oxidative stress. Using Principal Components Analysis, we could associate CPF reduction in esterases activity with swimming alterations, at 0.5 mg/L of the toxicant. Biochemical biomarkers reported here respond at levels 20 times lower than the LC50‐96 h and were associated with a biologically important response– swimming behavior. The link of responses across different levels of biological organization was here demonstrated. The species is suited as a model for ecotoxicological studies at different levels, including the individual and biochemical level, and may be considered a good reference organism in environmental control programs.

Environmental quality guideline values and remediation targets, specific to Antarctic ecosystems, are required for the risk assessment and remediation of contaminated sites in Antarctica. Ecotoxicological testing with Antarctic soil organisms is fundamental in determining reliable contaminant effect threshold concentrations. The present study describes the development of optimal culturing techniques and aqueous toxicity test procedures for an endemic Antarctic soil nematode, Plectus murrayi, which lives within interstitial waters between soil particles. Toxicity tests were of extended duration to account for the species’ physiology and life‐history characteristics. Plectus murrayi was sensitive to aqueous copper with a 50% effective concentration for egg‐hatching success of 139 µg/L. Hatched juveniles that were first exposed to copper as eggs appeared to be less sensitive than those first exposed at the hatched J2 stage, indicating a potential protective effect of the egg. Sensitivity of juveniles to copper increased with exposure duration, with 50% lethal concentrations of 478 and 117 µg/L at 21 and 28 d, respectively. The present study describes new methods for the application of an environmentally relevant test species to the risk assessment of contaminants in Antarctic soil and provides the first estimates of sensitivity to a toxicant for an Antarctic terrestrial microinvertebrate. Environ Toxicol Chem 2020;00:1–10. © 2019 SETAC

We describe two artificial stream experiments that exposed aquatic insect communities to Zn, Cu, and Cd (year 2014) and to Zn, Cu, and Ni (year 2015). The testing strategy was to concurrently expose insect communities to single metals and mixtures. Single metals tests were repeated to evaluate 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 metals treatments and effects concentrations could be predicted effectively from metals concentrations in either periphyton or in water. Most responses were similar in the replicated tests, but EC50 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 metals SSDs. The approach of testing translocated aquatic insect communities in 30‐day artificial streams is an efficient approach to generate multiple species effects values under quasi‐natural conditions that are relevant to natural streams.

Chlorination is commonly used to control biofouling organisms, however, chlorine rapidly hydrolyses in seawater to hypochlorite which undergoes further reaction with bromide, then with organic matter. These reaction products collectively termed chlorine‐produced oxidants (CPOs) can be toxic the marine biota. Because the lifetime of the most toxic forms is limited to several days, appropriate guideline values (GVs) need to be based on short‐term (acute) toxicity tests, rather than chronic tests. Flow‐through toxicity tests that provide continuous CPO exposure are the most appropriate, whereas static‐renewal tests generate variable exposure and effects dependent on the renewal rate. Literature data for acute CPO toxicity from flow‐through tests together with values from two sensitive 15‐min static tests, comprised 30 species from 9 taxonomic groups. These values were used in a species sensitivity distribution (SSD) to derive GVs that were protective of 99, 95 and 90% of species of 2.2, 7.2 and 13 µg CPO/L respectively. These are the first marine GVs for chlorine to be derived using SSDs, with all other international GVs being of unknown reliability being based on the use of assessment factors applied to data for the most sensitive species. In applying these conservative GVs in field situations, it would need to be demonstrated that concentrations of CPOs would be reduced to below the GV within an acceptable mixing zone both through dilution and dissociation.

Water quality standards for cobalt (Co) have not been developed for the European Union or United States. The objective of this research was to produce freshwater Co toxicity data that could be used by both the EU and US to develop appropriate regulatory standards (i.e., Environmental Quality Standards [EQS] or Predicted No Effect Concentration [PNEC] in Europe and Ambient Water Quality Criteria [AWQC] or State Water Quality Standards (WQS) in the US). Eleven species, including algae, an aquatic plant, and several invertebrate and fish species, were used in the performance of acute and chronic Co toxicity tests. Acute median‐lethal or median effective concentration (LC50 or EC50) values ranged from 90.1 µg Co/L for the duckweed (Lemna minor), to 157,000 µg Co/L for the midge (Chironomus tentans). Chronic 10% effect concentration (EC10) values ranged from 4.9 µg Co/L for the duckweed, to 2,170 µg Co/L for rainbow trout (Oncorhynchus mykiss). Chronic 20% effect concentration (EC20) values ranged from 11.1 µg Co/L for the water flea (Ceriodaphnia dubia), to 2,495 µg Co/L for O. mykiss. Results indicated that invertebrate and algae/plant species are more sensitive to chronic Co exposures than fish. Acute‐chronic ratios (derived as acute LC50s divided by chronic EC20s) were lowest for juvenile O. mykiss (0.6) and highest for the snail, Lymnaea stagnalis (2,670). Following the European‐based approach and using EC10 values, species sensitivity distributions (SSD) were developed and a median hazardous concentration for 5% of the organisms (HC5,50%) of 1.80 µg Co/L was derived. Chronic EC20 values were used, also in a SSD approach, to derive a US EPA‐style final chronic value (FCV) of 7.13 µg Co/L.

Toxic effects of selenium (Se) contamination in freshwaters have been well‐documented. However, study of Se contamination has focused on lentic and larger‐order lotic systems, whereas headwater streams have received little scrutiny. In central Appalachia, surface coal mining is a common Se source to headwater streams, thus providing a useful system to investigate Se bioaccumulation in headwater food chains and possible longitudinal patterns in Se concentrations. Toward that end, we assessed Se bioaccumulation in 2 reference and 4 mining‐influenced headwater streams. At each stream, we sampled ecosystem media, including streamwater, particulate matter (sediment, biofilm, leaf detritus), benthic macroinvertebrates, salamanders, and fish, every 400 m along 1.2 and 1.6 km reaches. We compared media Se concentrations within and among streams and evaluated longitudinal trends in media Se concentrations. Selenium concentrations in sampled media were higher in mining‐influenced streams compared to reference streams. We found the highest Se concentrations in benthic macroinvertebrates; however, salamanders and fish bioaccumulated Se to potentially harmful levels in mining‐influenced streams. Only one stream demonstrated dilution of streamwater Se with distance downstream, and few longitudinal patterns in Se bioaccumulation occurred along our study reaches. Collectively, our work provides a field‐based assessment of Se bioaccumulation in headwater food chains, from streamwater to fish, and highlights the need for future assessments of Se effects in headwater streams and receiving downstream waters.

Unlike most other conventional petroleum products that are derived from crude oil, gas‐to‐liquids (GTLs) are petroleum products that are synthesized from natural gas (methane). This process results in GTL products having no sulfur and low aromatic content, so they should have less impact on human health and the environment compared to crude oil‐derived products. GTLs have been registered for use as non‐aqueous base fluids (NABFs) in drilling muds, which aid in the process of drilling wells for oil and gas extraction; it is through these uses and others that they enter terrestrial environments. The primary objective of this study was to determine whether GTLs were less toxic to terrestrial soil biota than conventional NABFs used for land‐based drilling, such as diesel and low toxicity mineral oil (LTMO). A second objective was to understand the fate and impact of these fluids under more realistic soil and aging conditions of a common west Texas (USA) oil producing region (i.e. sandy loam soil with low organic matter, hot arid climate). Acute terrestrial toxicity studies were conducted on the soft‐bodied terrestrial invertebrate earthworm (Eisenia fetida) along with three plant species ‐ alfalfa (Medicago stavia), thickspike wheatgrass (Elymus lanceolatus), and fourwing saltbrush (Atriplex canescens). We also assessed changes in microbial community structure of the soils following additions of NABF. Overall, the GTL NABFs had lower toxicity compared to conventional NABFs like diesel and LTMO, as measured by invertebrate toxicity, plant seed germination, and impact on the microbial community.

Blooms of the cyanobacterium Microcystis spp. could affect fish health through the ingestion of colonies as well as exposure to dissolved microcystins in the water column. The goal of this study was to evaluate the dietary exposure pathway through which Microcystis spp. blooms may affect the liver function and nutritional status using a novel approach involving multiple analytical methods to assess the potential risk. This study was conducted using Threadfin shad, Dorosoma petenense, (TFS) is a pelagic fish commonly exposed to Microcystis spp. blooms in the upper San Francisco Estuary (SFE). The approach incorporated published and optimized methods that offer multiple lines of evidence including in situ hybridization, immunohistochemistry, histopathology, condition factor indices, and nutritional profiles. Measurements of TFS health and tissue condition were conducted at sites where Microcystis was present or absent during the 2007 bloom season. The results showed that dietary exposure to fish from Microcystis blooms resulted in the accumulation of microcystin in the gut and liver tissues of TFS collected from the sites with blooms. Although toxicity endpoints were likely confounded by antecedent conditions, our findings demonstrate dietary exposure of Microcystis toxins to fish using a novel approach with multiple lines of evidence.

Heavy metal pollution is widespread in China, particularly in its mining regions. Mercury (Hg) concentrations in birds from Guizhou Province were recently reported to be above adverse effect levels, even in nonmining areas. We sampled birds to investigate whether Hg might be a threat near lead (Pb), zinc (Zn), and tin (Sn) mines in Guangxi Zhuang Autonomous Region. We measured concentrations of 8 metals/metalloids in feathers of 627 resident birds representing 60 species sampled across 14 sites on 5 rivers. We found that Hg concentrations (mean ± standard deviation, 1.27 ± 2.02 ppm) were lower than in the recent Guizhou study. Mercury had the fewest correlations with other metals/metalloids; the mined metals (Pb, Sn, Zn) had the most such correlations. Levels of cadmium (Cd; 1.12 ± 2.64 ppm), arsenic (As; 4.78 ± 17.11 ppm), and Pb (17.18 ± 24.49 ppm) were closer to thresholds of adverse effects or relatively high compared to other studies. With the exception of a few hot spots for Hg, Cd, and As near mines, metal/metalloid levels were fairly evenly distributed among sites, consistent with the regional occurrence of mineable ore deposits. It appears that Hg is not threatening to all avian species in China, although it may be problematic for some species near Hg mines. In addition to Hg, however, other metals/metalloids may pose wildlife health hazards. Environ Toxicol Chem 2019;00:1–10. © 2019 SETAC

Since 2009, the Canadian and Alberta governments have been developing monitoring plans for surface water quality and quantity of the lower Athabasca River and its tributaries (2010–2013). The objectives of the present study to the fish monitoring program were to 1) assess the current status of fish in a tributary of the lower Athabasca River, 2) identify existing differences between upstream reference and within the oil sands deposit exposure sites, and 3) identify trends/changes in fish performance indicators relative to historical studies. The present study examines the fish performance indicators in slimy sculpin (Cottus cognatus) in the Steepbank River, Alberta, in terms of growth, gonad size, condition, and hepatic 7‐ethoxyresorufin‐O‐deethylase (EROD) activity as an indicator of exposure to oil‐sands‐related compounds. The sampling program followed historical sampling methods (1999–2000) to provide comparable data over time with an additional upstream site (n = 2) added as development progressed. Consistent changes were documented in sculpin collected from downstream sections of the Steepbank River within the oil sands deposit (n = 2) in 2010 through 2013. Sculpin demonstrated increased liver size with corresponding induction of EROD activity consistent with historical data and reductions in energy investment relative to reproductive development and gonadal steroid production capacity. There was no consistent evidence of changes in fish performance indicators with increased surface mining development, particularly adjacent to the Steepbank River Mid site. Although physical development in the Steepbank watershed has increased over the last 15 yr, these results are consistent with historical data suggesting that the magnitude of the response in the aquatic environment adjacent to the development has not changed. Environ Toxicol Chem 2019;00:1–14. © 2019 SETAC

We compared the toxicity of the neonicotinoids imidacloprid, thiacloprid, thiamethoxam, acetamiprid, and clothianidin in terms of the survival and reproduction of 2 species of soil invertebrates, Folsomia candida and Eisenia andrei. Tests were performed using LUFA 2.2 natural soil, following standard protocols aimed at answering 2 questions: 1) Is there a difference in the toxicity between pure compound and its formulation? and 2) Is there a difference in the sensitivity of the species exposed to the same compound? For E. andrei, formulations and pure compounds had similar toxicity to both endpoints tested. For F. candida, acetamiprid and imidacloprid had different toxicities, with acetamiprid being 4 times more toxic to survival (median lethal concentration [LC50] 0.12 mg active substance [a.s.]/kg dry soil) and imidacloprid being 4 times more toxic to reproduction of the springtail (median effect concentration [EC50] 0.25 mg a.s./kg dry soil) than their commercial formulations. The most toxic compound to E. andrei was acetamiprid (LC50 0.80 and EC50 0.35–0.40 mg a.s./kg), and the most toxic to F. candida was clothianidin (LC50 0.07 and EC50 0.05 mg a.s./kg). Estimated risk ratios indicated that only one application/yr of clothianidin in the formulation Poncho® may pose a threat to the populations of springtails and earthworms. Environ Toxicol Chem 2019;00:1–8. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Tissue distributions and body‐size dependent and species‐specific bioaccumulation of 12 organic ultraviolet absorbents (UVAs) were investigated in 9 species of wildlife freshwater fish from the Pearl River catchment, South China. The concentrations of the 12 UVAs were from 109 to 2320 ng/g lipid weight in the fish tissue samples. The UVAs 2‐hydroxy‐4‐methoxybenzophenone (BP‐3), octocrylene (OCR), UV531, and 5 benzotriazole UV stabilizers (UVP, UV329, UV234, UV328, and UV327) were detected in more than half of the fish tissue samples. The UVA UV531 showed an obvious potential for bioaccumulation in the wild freshwater fish, with an estimated bioaccumulation factor (log BAF) and a biota–sediment accumulation factor (BSAF) of 4.54 ± 0.55 and 4.88 ± 6.78, respectively. Generally, liver (989 ± 464 ng/g lipid wt) contained the highest level of UVAs, followed in decreasing order by belly fat (599 ± 318 ng/g lipid wt), swimming bladder (494 ± 282 ng/g lipid wt), dorsal muscle (470 ± 240 ng/g lipid wt), and egg (442 ± 238 ng/g lipid wt). The bioaccumulation of UVAs in the freshwater wild fish was species specific and compound dependent. Bottom‐dwelling detritus‐ingesting omnivorous fish contained obviously higher UVA concentrations, suggesting that detritus/sediment ingestion is a significant pathway for exposure of the wild freshwater fish to the UVAs. The UVAs UV531 and BP‐3 demonstrated a potential for growth dilution. Metabolism might play a significant role in elimination of the UVAs in the fish tissues, with the highest rate of metabolism in the liver. The UVAs did not demonstrate obvious trophic magnification in the freshwater ecosystem of the Pearl River catchment. More research is warranted to elucidate maternal transfer of the UVAs. Environ Toxicol Chem 2019;00:1–9. © 2019 SETAC

Tangshan city in Hebei Province is one of the most heavily polluted cities in China, with substantial industrial emissions. The development of effective air pollution emission reduction policies requires knowledge of the sources and health risks of polycyclic aromatic hydrocarbon (PAH)‐enriched fine particulate matter (PM2.5). We investigated the seasonal variation and source apportionment of 16 priority PAH‐enriched PM2.5 samples in Tangshan during 2014 and 2015, and we assessed the health risks associated with inhalation exposure to PAHs. The PM2.5 samples were collected from April 2014 to February 2015. We analyzed the concentrations of PM2.5 and PAH‐enriched PM2.5, and used principal component analysis and molecular diagnostic ratios to identify potential sources. We explored the relationship between distribution and meteorological conditions, and used an incremental lifetime cancer risk (ILCR) model to quantitatively evaluate exposure from the inhalation risk of PAHs. The average mass concentration of PM2.5 was 196 µg/m3, with a range 34.0 to 586 µg/m3. The median ∑16PAH values in PM2.5 were 190 ng/m3, with a range of 60.2 to 862 ng/m3 over the sampling period. The order of ∑16PAHs concentration was winter > autumn > summer > spring. The results show that the primary sources of PAH‐enriched PM2.5 are coal combustion, vehicle exhaust, and biomass burning. The annual mean of benzo[a]pyrene (BaP) was 8.37 ng/m3, more than 8‐fold greater than the BaP annual standard (1 ng/m3) set by the Chinese State Environmental Protection Agency. The ILCR values for 3 groups (children, teenagers, and adults) over the 4 seasons were between 10–6 and 10–4, indicating a potential health risk from PAHs in Tangshan. Environ Toxicol Chem 2019;00:1–10. © 2019 SETAC

Pesticides used in seed coatings can influence seed consumption by birds and, therefore, actual exposure risk for them. A quantification of such effects on consumption is currently not regarded as a refinement factor in environmental risk assessments, although it is a possible option and should be considered, for example, for comparing exposure risk of different pesticides. It can highlight avoidance behavior, preventing birds from taking up lethal or sublethal pesticide doses. To formulate a standard, we developed an indoor test procedure based on established pen test methods, including 2‐ and no‐choice phases with hunger periods. During testing, the highest standards of animal welfare were applied. Statistical approaches were used to determine the most appropriate number of replicates and for analysis. The effect on consumption of seeds is expressed as the ratio of consumed treated to untreated seeds. This consumption factor can be applied in avian risk assessments for seed treatments equivalent to an avoidance factor. We present, as an example, an application of the procedure to obtain a seed‐ and species‐specific consumption factor for oilseed rape seeds (Brassica napus) provided untreated and treated with fungicides to greenfinches (Carduelis chloris) and Japanese quail (Coturnix japonica). Overall, bird constitution was not negatively affected by the test procedure in either species. The test procedure was suitable for showing differences in expected consumption patterns, such as greater avoidance of treated seeds in 2‐choice than in no‐choice tests. However, the consumption differed between species and fungicide treatments, allowing us to rank avoidance effects of different fungicides. Using the presented standard procedure to generate comparable pesticide‐ and species‐specific consumption factors for more species and seed treatments may result in refinement of default values and reduce animal trials in different designs in the future. Environ Toxicol Chem 2019;00:1–12. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

The aquatic ecological environment is being threatened from overuse of pesticides, and the aquatic toxicity toward rainbow trout (Oncorhynchus mykiss) plays a significant role in environmental risk assessment of agrochemicals. In the present study, 2 norm index formulas were developed, from which several norm descriptors were derived. A quantitative structure–activity relationship (QSAR) model was established for the prediction of acute toxicity (median lethal concentration) toward rainbow trout of various pesticides. Results indicated that the present QSAR model presented an R2 of 0.8053. Meanwhile, internal validation (QLOO2 = 0.7606), external validation (Rtraining2 = 0.8011, Rtesting2 = 0.8108), Y‐randomization test, and applicability domain analysis further demonstrated the stability, reliability, and wide application domain of the present QSAR model. Accordingly, these norm descriptors might be applicable to the structures of pesticides for predicting the acute toxicity to aquatic organism. Environ Toxicol Chem 2019;00:1–7. © 2019 SETAC

Melanophores are pigmented cells that change the distribution of melanosomes, enabling animals to appear lighter or darker for camouflage, thermoregulation, and protection from ultraviolet radiation. A complex series of hormonal and neural mechanisms regulates melanophore pigment distribution, making these dynamic cells a valuable tool to screen toxicants as they rapidly respond to changes in the environment. We found that maltol, a naturally occurring flavor enhancer and fragrance agent, induces melanophore pigment aggregation in a dose‐dependent manner in Xenopus laevis tadpoles. To determine if maltol affects camouflage adaptation, we placed tadpoles into maltol baths situated over either a white or a black background. Maltol induced pigment aggregation in a similar dose‐dependent pattern regardless of background color. We also tested how maltol treatment compares to melatonin treatment and found that the degree of pigment aggregation induced by maltol is similar to treatment with melatonin but that maltol induces over a much longer time course. Last, maltol had no effect on mRNA expression in the brain of genes that regulate camouflage‐related pigment aggregation. The present results suggest that maltol does not exert its effects via the camouflage adaptation mechanism or via melatonin‐related mechanisms. These results are the first to identify a putative toxicological effect of maltol exposure in vivo and rule out several mechanisms by which maltol may exert its effects on pigment aggregation. Environ Toxicol Chem 2019;00:1–15. © 2019 SETAC

Active biomonitoring approaches are now recognized as relevant for monitoring water contamination and toxicity. Nevertheless, due to the confounding influence of variable and uncontrolled environmental conditions such as temperature, biological markers measured on transplanted individuals to assess water quality are difficult to interpret. The purpose of this study aims is to propose a methodology for adapting a laboratory test of chronic sub‐lethal toxicity based on the molting cycle of Gammarus fossarum to in situ assays. To this end, we (1) adapted the molt cycle temperature‐dependent model developed in Part 1 to the fluctuating temperatures measured in the field; (2) assessed the predictive power of our approach as “reference value” from gammarids caged in nine non‐impacted sites at different seasons; and (3) tested the relevance of our tool to interpret in situ reproductive bioassays from five upstream/downstream studies and a large‐scale deployment in twelve sites. Our approach based on modeling the progress of gammarid molting cycle as a function of temperature appeared as a relevant and robust tool for interpreting in situ observations in different environmental contexts in time and space. By avoiding using a “reference” or upstream situation as a baseline from which water quality could be assessed, this approach provides a real added value to water quality diagnosis in biomonitoring programs.

A former mining site has been the subject of extensive remediation and restoration, with a significant focus on disconnecting mine spoils from groundwater and managing the quantity and quality of runoff. A remaining task is ensuring concentrations of zinc (Zn) in the stream outflow of a pit lake are reduced below water quality standards. The efficacy of multiple capping materials for decreasing Zn dissolution from sediments was conducted under natural and reasonable worst‐case conditions (pH = 5.5). Capping materials included AquaBlok™, limestone, and limestone–bone char. Field exposures were conducted in limnocorrals that isolated overlying water columns above the sediment and capping treatments. Simultaneous in situ and ex situ toxicity tests were conducted using Daphnia magna, Hyalella azteca, and Chironomus dilutus. In situ caged organisms were protected from temperature shock (warm epilimnetic waters) by deploying within a Toxicity Assessment Container System (TACS). Organisms were exposed to surficial sediments, caps, and hypolimnetic overlying waters for 4 d. Ex situ testing was conducted in core tube mesocosms containing sediments and caps at similar temperatures (15–19 °C). Results demonstrated the usefulness of TACS deployment in stratified lake systems. There were no differences in responses between treatments involving sediment capping materials in both in situ and ex situ tests. The lack of differences was likely due to dissolved Zn in surface water being below the hardness‐adjusted threshold effects levels (164 μg L–1). This field‐ and laboratory‐based weight‐of‐evidence study provided site‐specific data to support the selection of an effective remedy, with reduced uncertainty compared to laboratory and chemistry‐only approaches. Environ Toxicol Chem 2019;39:240–249. © 2019 SETAC

Maternal transfer of persistent organic pollutants (POPs) confronts developing embryos with a pollution legacy and poses conservation concerns due to its potential impacts unto subsequent generations. We conducted a systematic review focusing on: 1) processes of POP maternal transfer, 2) challenges and opportunities to synthesizing current knowledge on POP concentrations in eggs, and 3) a meta‐analysis of patterns in current egg pollution data. Results suggest selective maternal transfer of individual compounds. These relate to biological factors such as the foraging and remigration behavior, and to the selective mobilization of POPs during vitellogenesis, such as increased diffusion limitation for lipophilic POPs and slower release and higher reabsorption of apolar POPs. A key gap relates to knowledge of further selective toxicokinetics during embryonic development, as research to date has mainly focused on initial uptake into eggs. Challenges in the synthesis of current data on egg contamination profiles relate to methodological differences, varying analytical approaches, restricted data access, and reporting transparency among studies. To increase opportunities in the use of current data, we propose best practice guidelines, and synthesize a database on POP concentrations within sea turtle eggs. The meta‐analysis revealed a geographical and taxonomic bias on the West Atlantic Ocean, including the Gulf of Mexico and Caribbean Sea, with most studies conducted on green turtles. Concentrations of POPs show temporal patterns related to trends in usage, production, release, and persistence in the environment, often with regional patterns. The trophic level has the potential to influence POP patterns with higher concentrations in loggerheads compared to other species, but this is confounded by temporal and geographic trends. We argue for more mechanistically process‐focused and methodologically comparable research. Environ Toxicol Chem 2019;39:9–29. © 2019 SETAC

No‐observed‐effect concentrations (NOECs) are used in environmental hazard classification and labeling of chemicals and their environmental risk assessment. They are typically obtained using standard tests such as the fish early‐life stage (FELS) toxicity test, the chronic Daphnia reproduction test, and the algae growth inhibition test. Given the demand to replace and reduce animal tests, we explored the impact of the FELS toxicity test on the determination of effect concentrations by comparing the FELS toxicity test and the Daphnia and algae acute or chronic toxicity tests. Lowest‐observed‐effect concentrations (LOECs) were used instead of NOECs for better comparison with median lethal or effect concentration data. A database of FELS toxicity data for 223 compounds was established. Corresponding Daphnia and algae toxicity tests were identified using established databases (US Environmental Protection Agency ECOTOX, Organisation for Economic Co‐operation and Development QSAR Toolbox, eChemPortal, EnviroTox, and OpenFoodTox). Approximately 9.5% of the investigated compounds showed a 10‐fold higher sensitivity with the FELS toxicity test in comparison with the lowest effect concentrations obtained with any of the other tests. Some of these compounds have been known or considered as endocrine disrupting, or are other non‐narcotic chemicals, indicating that the higher sensitivity in the FELS toxicity test is related to a specific mechanism of action. Targeting these mechanisms by alternative test systems or endpoints, using fish embryos for instance, may allow reduction or replacement of the FELS toxicity test or may allow us to prioritize compounds for conduction of the FELS toxicity test. Environ Toxicol Chem 2019;39:30–41. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

A Society of Environmental Toxicology and Chemistry technical workshop was held in December 2017 to critically evaluate the current state of the science of metal bioavailability modeling. The availability of mechanistic models such as the biotic ligand model and the rapid development of empirical models such as multiple linear regressions means that choices are available in terms of bioavailability normalization approaches that can be used in metal risk assessments and the development of risk‐based protective values for aquatic life. A key goal of the workshop was to provide potential users of metal bioavailability models with the information required to make appropriate decisions when choosing among mechanistic and empirical models. Workshop participants focused on the state of the science of metal bioavailability modeling, mechanistic and empirical model frameworks, validation of bioavailability models, and application of bioavailability models in risk‐based decision‐making approaches. The output of this workshop provides the necessary scientific information to incorporate bioavailability normalization in regulations pertaining to metals in freshwater systems. Environ Toxicol Chem 2019;39:42–47. © 2019 SETAC

Many metals (aluminum, cadmium, cobalt, copper, nickel, lead, zinc) are widely studied environmental contaminants because of their ubiquity, potential toxicity to aquatic life, and tendency for toxicity to vary widely as a function of water chemistry. The interactions between metal and water chemistry influence metal “bioavailability,” an index of the rate and extent to which the metal reaches the site of toxic action. The implications of metal bioavailability for ecological risk assessment are large, with as much as a 100‐fold variability across a range of water chemistries in surface waters. Beginning as early as the 1930s, considerable research effort was expended toward documenting and understanding metal bioavailability as a function of total and dissolved metal, water hardness, natural organic matter, pH, and other water characteristics. The understanding of these factors and improvements in both analytical and computational chemistry led to the development of modeling approaches intended to describe and predict the relationship between water chemistry and metal toxicity, including the free ion activity model, the gill surface interaction model, the biotic ligand model, and additional derivatives and regression models that arose from similar knowledge. The arc of these scientific advances can also be traced through the evolution of the US Environmental Protection Agency's ambient water quality criteria over the last 50 yr, from guidance in the “Green Book” (1968) to metal‐specific criteria produced in the last decade. Through time, water quality criteria in many jurisdictions have incorporated increasingly sophisticated means of addressing metal bioavailability. The present review discusses the history of scientific understanding of metal bioavailability and the development and application of models to incorporate this knowledge into regulatory practice. Environ Toxicol Chem 2019;39:48–59. © 2019 SETAC

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

Recently, there has been renewed interest in the development and use of empirical models to predict metal bioavailability and derive protective values for aquatic life. However, there is considerable variability in the conceptual and statistical approaches with which these models have been developed. In the present study, we review case studies of empirical bioavailability model development, evaluating and making recommendations on key issues, including species selection, identifying toxicity‐modifying factors (TMFs) and the appropriate environmental range of these factors, use of existing toxicity data sets and experimental design for developing new data sets, statistical considerations in deriving species‐specific and pooled bioavailability models, and normalization of species sensitivity distributions using these models. We recommend that TMFs be identified from a combination of available chemical speciation and toxicity data and statistical evaluations of their relationships to toxicity. Experimental designs for new toxicity data must be sufficiently robust to detect nonlinear responses to TMFs and should encompass a large fraction (e.g., 90%) of the TMF range. Model development should involve a rigorous use of both visual plotting and statistical techniques to evaluate data fit. When data allow, we recommend using a simple linear model structure and developing pooled models rather than retaining multiple taxa‐specific models. We conclude that empirical bioavailability models often have similar predictive capabilities compared to mechanistic models and can provide a relatively simple, transparent tool for predicting the effects of TMFs on metal bioavailability to achieve desired environmental management goals. Environ Toxicol Chem 2019;39:85–100. © 2019 SETAC

Regulatory jurisdictions worldwide are increasingly incorporating bioavailability‐based toxicity models into development of protective values (PVALs) for freshwater and saltwater aquatic life (e.g., water quality criteria, standards, and/or guidelines) for metals. Use of such models for regulatory purposes should be contingent on their ability to meet performance criteria as specified through a model‐validation process. Model validation generally involves an assessment of a model's appropriateness, relevance, and accuracy. We review existing guidance for validation of bioavailability‐based toxicity models, recommend questions that should be addressed in model‐validation studies, discuss model study type and design considerations, present several new ways to evaluate model performance in validation studies, and suggest a framework for use of model validation in PVAL development. We conclude that model validation should be rigorous but flexible enough to fit the user's purpose. Although a model can never be fully validated to a level of zero uncertainty, it can be sufficiently validated to fit a specific purpose. Therefore, support (or lack of support) for a model should be presented in such a way that users can choose their own level of acceptability. We recommend that models be validated using experimental designs and endpoints consistent with the data sets that were used to parameterize and calibrate the model and validated across a broad range of geographically and ecologically relevant water types. Environ Toxicol Chem 2019;39:101–117. © 2019 SETAC

The primary goal of the present study is to provide a broad view of best practices for evaluating bioavailability models for metals for use in the protection of aquatic life. We describe the state of the science regarding 1) the evaluation and selection of ecotoxicity data, 2) the selection of bioavailability models for use in normalization, and 3) subsequent application of bioavailability models. Although many examples of normalization steps exist worldwide, a scheme is proposed to evaluate and select a model that takes account of its representativeness (water chemistry and taxonomic coverage of the ecotoxicity data set) and validation performance. Important considerations for a suitable model are the quantity of inputs needed, accuracy, and ease of use, all of which are needed to set protective values for aquatic life and to use these values to evaluate potential risks to organisms in receiving waters. Although the end results of different model application approaches may be broadly similar, the differences in these application frameworks ultimately come down to a series of trade‐offs between who needs to collect the data and use the bioavailability model, the different requirements of spatial scales involved (e.g., regional vs site‐specific values), and model predictiveness and protectiveness. Ultimately, understanding the limits and consequences of these trade‐offs allows for selection of the most appropriate model and application framework to best provide the intended levels of aquatic life protection. Environ Toxicol Chem 2019;39:118–130. © 2019 SETAC

Cerium oxide nanoparticles (CeO2 NPs) are included in the Organisation for Economic Co‐operation and Development (OECD) priority list of engineered nanomaterials for assessment of their environmental impact. The present study was carried out to assess the CeO2 NP toxicity to the freshwater midge Chironomus riparius larvae at concentrations of 2.5, 25, 250, and 2500 mg of CeO2 NP/kg of sediment. Experiments were designed to assess the prolonged exposure of midges to CeO2 NPs while adhering to OECD test guideline 218. The following parameters were investigated: CeO2 NP uptake by larvae, oxidative stress parameters, in vivo genotoxic effects, and life trait parameters. Inductively coupled plasma–mass spectrometry analysis showed a significant positive correlation between the concentration of CeO2 NPs in the sediment and its uptake by the larvae. No significant mortality was observed in C. riparius, and oxidative stress was not detected. The only significantly induced sublethal effect was genotoxicity, which began to manifest at a lowest‐observed‐effect concentration of 25 mg kg–1 of sediment and progressively increased at higher concentrations. Our results indicate that exposure to CeO2 NP–contaminated freshwater sediments does not pose a risk to chironomids at environmentally realistic concentrations. However, the significant accumulation of CeO2 NPs by chironomid larvae may pose a risk through trophic transfer to organisms further up the food chain. Environ Toxicol Chem 2019;39:131–140. © 2019 SETAC

Early–life stage (ELS) toxicity tests are recognized as an advancement over current testing methodologies in terms of cost, animal use, and biological relevance. However, standardized ELS tests are not presently available for some vertebrate taxa, including birds. The present study describes a Japanese quail (Coturnix japonica) ELS test that is a promising candidate for standardization and applies it to test 8 environmental chemicals (ethinylestradiol, benzo[a]pyrene, chlorpyrifos, fluoxetine, lead(II)nitrate, trenbolone, seleno‐L‐methionine, hexabromocyclododecane). Individual chemicals were injected into the air cell of unincubated Japanese quail eggs at 3 concentrations, all predicted to cause ≤20% mortality. Survival to embryonic day 16 was consistently high (>90%) among the vehicle‐injected controls. All chemicals, except ethinylestradiol, were detected in liver tissue, most at concentrations suggestive of embryonic clearance. Adverse effects were observed for 5 of the 8 chemicals; chlorpyrifos (41.1 µg/g) significantly increased developmental abnormalities and decreased embryo and gallbladder mass. Ethinylestradiol (54.2 µg/g) and hexabromocyclododecane (0.02 µg/g) decreased embryo mass and tarsus length, respectively. Benzo[a]pyrene (0.83 µg/g) and fluoxetine hydrochloride (32.7 µg/g) exceeded the 20% mortality cutoff. No effects were observed following lead(II)nitrate, seleno‐L‐methionine, or trenbolone exposure up to 10.7, 0.07, and 4.4 µg/g, respectively. Overall, our ELS approach was time‐ and cost‐effective, caused minimal mortality in controls, effectively delivered diverse chemicals to the embryo, and permitted identification of apical outcomes, all of which provide support toward standardization. Environ Toxicol Chem 2019;39:141–154. © 2019 SETAC

Amphibians are in global decline, and anthropogenic activities are known leading causes of their demise. Thus the interaction between agriculture and amphibian health has been examined for decades. Many facets of amphibian physiology and ecology place them at high risk among the nontarget organisms affected by agricultural byproducts. Research has shown that many chemicals and fertilizers affect amphibian growth, reproduction, and survival. The impacts differ based on the type of agricultural byproduct (e.g., chemical pesticide or nutrient‐heavy fertilizer) and amphibian species, but the effects are usually negative. However, minimal research exists on how organic biopesticides interact with amphibian populations. Biopesticides utilize insecticidal bacteria as the active ingredient in lieu of synthetic chemicals. The inert ingredients present in biopesticide commercial products are considered safe to nontarget organisms. The present study tested the impacts of a commercial biopesticide on the survival of amphibian embryos and larvae. We found that expected environmental concentrations of the microbial biopesticide Monterrey B.t. did not significantly reduce survival in embryos or larvae. However, the higher doses used to assess threshold toxicity levels caused significant mortality. Our data suggest that biopesticides are not directly harmful to amphibian embryos or larvae in concentrations regularly applied for pest control. Environ Toxicol Chem 2019;39:155–161. © 2019 SETAC

2,2′,3,5′,6‐Pentachlorobiphenyl (PCB‐95) is an environmental neurotoxicant. There is accumulated evidence that some neurotoxic effects of PCB‐95 are caused by increased spontaneous Ca2+ oscillations in neurons resulting from modifying ryanodine receptors (RyR) in calcium‐releasing channels. However, there are large gaps in explaining brain and other developmental malformations on embryonic PCB‐95 exposure. In the present study, we address those deficiencies by studying the toxic effects of PCB‐95 using zebrafish as an ontogenetic model. To characterize these effects, zebrafish embryos with intact chorions were exposed to 4 different concentrations of PCB‐95 (0.25, 0.5, 0.75, and 1 ppm) for 3 consecutive days. The controls were maintained in 0.5 × E2 medium or egg water and in 0.1% (v/v) dimethyl sulfoxide (DMSO)/0.5 × E2 medium or egg water. PCB‐95‐treated groups showed dose‐dependent decreases in survival and hatching rates, with increased rates of developmental malformations when compared to controls. These include morphological malformations, brain cell necrosis, and smaller eye sizes at 5 d post fertilization. These data suggest potential mechanisms underlying the abnormal behavior observed in a visual stimulus assay. The present study provides insight into PCB‐95‐induced developmental toxicity and supports the use of the zebrafish model in understanding the effects of PCB‐95 exposure. Environ Toxicol Chem 2019;39:162–170. © 2019 SETAC

The Organisation for Economic Co‐operation and Development guideline 305 for bioaccumulation testing in fish includes the option to conduct a dietary test for assessing a chemical's bioaccumulation behavior. However, the one‐compartment toxicokinetic model that is used in the guidelines to analyze the results from dietary bioaccumulation tests is not consistent with the current state of the science, experimental practices, and information needs for bioaccumulation and risk assessment. The present study presents 1) a 2‐compartment toxicokinetic modeling framework for describing the bioaccumulation of neutral hydrophobic organic chemicals in fish and 2) an associated toxicokinetic analysis tool (absorption, distribution, metabolism, and excretion [ADME] B calculator) for the analysis and interpretation of dietary bioaccumulation test data from OECD‐305 dietary tests. The model framework and ADME‐B calculator are illustrated by analysis of fish dietary bioaccumulation test data for 238 substances representing different structural classes and susceptibilities to biotransformation. The ADME of the chemicals is determined from dietary bioaccumulation tests and bioconcentration factors, biomagnification factors, and somatic and intestinal biotransformation rates. The 2‐compartment fish toxicokinetic model can account for the effect of the exposure pathway on bioaccumulation, which the one‐compartment model cannot. This insight is important for applying a weight‐of‐evidence approach to bioaccumulation assessment where information from aqueous and dietary test endpoints can be integrated to improve the evaluation of a chemical's bioaccumulation potential. Environ Toxicol Chem 2019;39:171–188. © 2019 SETAC

Vicuna is a wild, endangered species of Andean camelid living in the hyperarid Andean plateau. In the central part of the plateau, the Lithium Triangle defines a zone with lithium‐rich salt pans. Brine pools naturally form within the salt pans, and the adaptation strategy of vicuna consists of drinking from brine pools. Together with reporting the first chemical data on vicuna bones and teeth, we analyzed lithium, boron, and arsenic in water and brines, with the aim of assessing their relation to chronic exposure by water ingestion. We collected and analyzed bones of vicuna specimens lying in an Andean salt pan, together with brine and water samples. Brine and water samples are highly saline and contain large amounts of lithium, boron, and arsenic. Lithium (13.50–40 mg kg–1) and boron (40–46.80 mg kg–1), but not arsenic, were found in the vicuna bones and teeth. Based on our results and on previously reported data on human tissues in the Andes, we conducted statistical assessments of the relationships between lithium and boron in body tissues and water samples, and discuss their environmental significance in the context of the Lithium Triangle. Environ Toxicol Chem 2019;39:200–209. © 2019 SETAC

To assess potential impacts on receiving systems, associated with storm water contaminants, laboratory 10‐d amphipod (Eohaustorius estuarius) survival toxicity tests were performed using intact sediment cores collected from Paleta Creek (San Diego Bay, CA, USA) on 5 occasions between 2015 and 2017. The approach included deposition‐associated sediment particles collected from sediment traps placed at each of 4 locations during the 2015 to 2016 wet seasons. The bioassays demonstrated wet season toxicity, especially closest to the creek mouth, and greater mortality associated with particles deposited in the wet season compared with dry season samples. Grain size analysis of sediment trap material indicated coarser sediment at the mouth of the creek and finer sediment in the outer depositional areas. Contaminant concentrations of metals (Cd, Cu, Hg, Ni, Pb, and Zn) and organic compounds (polycyclic aromatic hydrocarbons [PAHs], polychlorinated biphenyls [PCBs], and pesticides) were quantified to assess possible causes of toxicity. Contaminant concentrations were determined in the top 5 cm of sediment and porewater (using passive samplers). Whereas metals, PAHs, and PCBs were rarely detected at sufficient concentrations to elicit a response, pyrethroid pesticides were highly correlated with amphipod toxicity. Summing individual pyrethroid constituents using a toxic unit approach suggested that toxicity to E. estuarius could be associated with pyrethroids. This unique test design allowed delineation of spatial and temporal differences in toxicity, suggesting that storm water discharge from Paleta Creek may be the source of seasonal toxicity. Environ Toxicol Chem 2019;39:229–239. © 2019 SETAC

Monitoring the adverse effects of environmental contaminants on the reproduction of invertebrate species in the field remains a challenge in aquatic ecotoxicology. To meet the need for reliable tools for in situ toxicity assessment, this report presents the first part of a methodological study of the in situ implementation of a reproductive bioassay in Gammarus previously developed for screening the toxicity of chemical compounds during laboratory exposure. To ensure the correct interpretation of the modulation of reproductive markers (molting, fecundity, follicle growth, embryonic development) in uncontrolled environmental conditions, we experimentally assessed and statistically modelled the variability in the female reproductive cycle during laboratory exposure under several temperature and water hardness conditions. While water hardness did not influence the reproductive cycle, the significant accelerating effect of temperature on the dynamics of molting and marsupial development was finely modelled, by detailing the influence of temperature on the probability of transition between all molt and embryonic stages along the female cycle. In addition, no effect of temperature or water hardness was detected on the number of oocytes and embryos carried by females. Furthermore, the finding that the relative durations of the first four molt and embryonic stages are constant whatever the temperature makes it possible to predict the molting dynamics in fluctuating temperature conditions. Since this could allow us to take into account the confounding influence of temperature on the measurement of reproductive makers, the implications of these findings for an optimal in situ implementation of the reproductive bioassay with G. fossarum are discussed. The relevance of this modelling approach during in situ implementation is tested in a companion report of this study.

Regulatory environmental risk assessment (ERA), applied to establish a protection limit for all bacterial diversity in surface waters, relies on a growth inhibition test performed upon a single species of cyanobacteria and the activated sludge respiration inhibition test (ASRIT). Recently, the ability of this approach to protect adequately for bacteria that provide important ecosystem services has been questioned and empirical data for additional species to further investigate the effectiveness of the ERA is urgently required. Here, we present the development and validation of a cost effective and time efficient microplate assay for measurement of chemicals exposure on cyanobacteria growth rate that is comparable to the traditional shake flask test. The assay has been optimised to ensure comparisons of cyanobacteria sensitivity under exponential growth are assessed across equivalent experimental conditions using phycocyanin fluorescence as a surrogate for cell density. The test system is validated using potassium dichromate and the results compared to those obtained in an OECD 201 shake flask test system. This assay is suitable for the screening of new and legacy chemicals, including antibiotics, lacking ecotoxicology data across a wide range of cyanobacteria for more comprehensive ERA.

Coal‐related elements are toxic and persistent pollutants that have spread globally since the industrial revolution, mainly from point‐source emissions. A sediment core was collected from Deep Lake in northeastern Washington State (USA) by the Washington State Department of Ecology, with the aim of assessing recent changes in atmospheric deposition in the US Pacific Northwest. The core was divided into depth intervals and dated by lead‐210. A sample from each cross section was digested and analyzed for toxic metals and metalloids using inductively coupled plasma–mass spectrometry. Data show recent increases in the concentrations of arsenic, barium, selenium, and mercury. Comparison with 1993 US Geological Survey ice core data from the Upper Fremont Glacier in Wyoming (USA), Asian coal consumption data, and weather patterns suggests that pollutant inputs to Deep Lake sediments are the result of coal‐burning activities in the Asia–Pacific region. Most notably, mercury deposition in Deep Lake has increased from approximately 20 ppb in 1996 to 9470 ppb in 2014 (an ~400‐fold increase), and since 1993 when the ice core was analyzed. Environ Toxicol Chem 2019;00:1–8. © 2019 SETAC

Tritium, a radioactive isotope of hydrogen of natural and anthropogenic origin, is ubiquitously present in the environment. Effluents of nuclear center of production are significant anthropogenic sources. With the upcoming project of thermonuclear fusion, tritium releases in the environment may increase. It is therefore important to characterize the ecological risk linked to tritium. The effects of tritiated water (HTO) were therefore studied in zebrafish larvae exposed during 10 days to different dose rates: 1.1x102, 4.1x102 and 3.8x103 µGy/h for larvae, corresponding respectively to a water contamination of 104, 105 and 106 Bq/mL of HTO. Those dose rates were higher than 10 μGy/h which is the threshold recommended to start monitoring ecosystems where radiological contaminants are present. Mortality, embryo‐larval development, immune‐, geno and neuro‐toxicity, and alterations of tissues were investigated. Results showed that tritiated water exposure induced DNA damage, ROS production and modulated the expression of genes involved in detoxification processes. Moreover, modifications of the muscular tissues (degradation of myofibrils at 4 dpf and disorganization of mitochondria at later stages) were observed. Results differed with HTO dose rates and with developmental stages. These results will drive future research for the development of new HTO‐sensitive biomarkers and will allow us to progress in the characterization of the modes of action of tritium in fish.

To fully assess the long‐term impacts of oil spills like the 2010 Deepwater Horizon incident in the northern Gulf of Mexico (GMx), the potential for organisms other than microbes to affect the fate and distribution of the oil may have to be considered. This influence could be substantial for abundant bioturbating benthic animals like the ghost shrimp Lepidophthalmus louisianensis. An assessment of the influence of these ghost shrimp on petroleum hydrocarbons was conducted in laboratory micro‐ and mesocosms containing coastal GMx sediment, seawater, and oil or the polynuclear aromatic hydrocarbon (PAH) pyrene. In an experiment with pyrene added to the water column, the ghost shrimp presence lowered water‐column pyrene concentrations. In an experiment with oil added to the sediment surface, the ghost shrimp presence decreased PAH concentrations in the sediment surface layer but increased these in the water column and subsurface sediment. A companion study and a mass‐balance analysis indicated a net loss of PAHs through an enhancement of microbial degradation. In an experiment in which oil was added as a narrow subsurface layer in the sediment, the ghost shrimp presence appeared to broaden the oil's depth distribution. Taken together, these results demonstrate that ghost shrimp can significantly influence the biodegradation and distribution of spilled oil in coastal ecosystems.

The Army is replacing traditional munitions with insensitive munitions (IM) resistant to accidental detonation. Although the parent IM compound nitroguanidine (NQ) is generally not acutely toxic at concentrations >1000 mg/L in aquatic exposures, products formed by intensive UV‐degradation resulted in multiple‐order of magnitude increase in toxicity. A methylated congener of NQ, 1‐methyl‐3‐nitroguanidine (MeNQ), is also being assessed for potential use in IM explosive formulations, therefore the present study investigated the hazard of parent versus UV‐degraded MeNQ using fathead minnows (Pimephales promelas). While up to 716 mg/L parent MeNQ caused no significant mortality or effects on growth in larval P. promelas fish in 7‐d exposures, a similar concentration of MeNQ subjected to UV‐treatment resulted in 85% mortality. The UV‐treatment degraded only 3.3% of the MeNQ (5,800 mg/L stock, UV‐treated for 6 h), indicating that MeNQ degradation products have potentially high toxicity. The parent MeNQ exposure caused significantly decreased transcriptional expression of genes within the significantly enriched insulin metabolic pathway suggesting antagonism of bioenergetics pathways which complements observed, although non‐significant, decreases in body weights. Significant differential transcriptional expression in the UV‐degraded MeNQ treatments resulted in significant enrichment of pathways and functions related to cell cycle, as well as erythrocyte function involved in O2/CO2 exchange. These functions represent potential mechanistic source(s) of increased toxicity observed in the UV‐degraded MeNQ exposures, which are distinct from previously observed mechanisms underlying increased toxicity of UV‐degraded NQ in fish.

In developing countries, household energy use is highly variable and complex, yet emissions arising from fuel combustion indoors are typically poorly quantified. Polycyclic aromatic hydrocarbons (PAHs) are emitted during the combustion of organic fuels such as charcoal and biomass. In this study, multi‐channel polydimethylsiloxane (PDMS) rubber traps were used for gas phase PAH sampling and were extracted using a low solvent volume plunger‐assisted solvent extraction (PASE) method. 16 U.S. Environmental Protection Agency priority PAHs primarily in the gas phase were investigated in indoor air of rural and urban residential homes in coastal Kenya (Mombasa and Taita Taveta counties) using typical combustion devices of each area. Average gaseous PAH concentrations per household were higher in rural (ranging from 0.81 to 6.09 µg m‐3) compared to urban homes (ranging from 0 to 2.59 µg m‐3), although ambient PAH concentrations were higher in urban environments, likely due to traffic contributions. The impact of fuel choice and thereby combustion device on PAH emissions was very clear, with the highest concentrations of PAHs quantified from wood burning emissions from 3‐stone stoves (total PAH averages of 46.23 ±3.24 µg m‐3 (n=6)). Average benzo[a]pyrene equivalent (BaPeq) total concentrations were evaluated for the priority PAHs and ranged from not detected to 43.31, 88.38, 309.61 and 453.88 ng m‐3 for gas, kerosene, jiko, 3‐stone and improved 3‐stone stoves, respectively.

Lack of consistent findings in different experimental settings remains to be a major challenge in toxicogenomics. The present study investigated, whether consistency between findings of different microarray experiments can be improved when the analysis is based on a common reference frame (“toxicogenomic universe”), which can be generated using the machine learning‐algorithm of the self‐organizing map (SOM). This algorithm arranges and clusters genes on a two‐dimensional grid according to their similarity in expression across all considered data. In the present study, nineteen data sets, comprising of 54 different adult fathead minnow liver exposure experiments, were retrieved from Gene Expression Omnibus and used to train a SOM. The resulting toxicogenomic universe aggregates 58,872 probes to 2,500 nodes and was used to project, visualize and compare the fingerprints of these 54 different experiments. For example, we could identify a common pattern, with 14% of significantly regulated nodes in common, in the data sets of an interlaboratory study of ethinylestradiol exposures, previously published by Feswick et al. (2017). Consistency could be improved compared to the 5% total overlap in regulated genes reported before. Furthermore, we could determine a specific and consistent estrogen‐related pattern of differentially expressed nodes and clusters in the toxicogenomic universe applying additional clustering steps and comparing all obtained fingerprints. This study shows that the SOM‐based approach is useful for generating comparable toxicogenomic fingerprints and improving consistency between results of different experiments.

Mortality of brook trout Salvelinus fontinalis and water chemistry were characterized in six headwater streams in the western Adirondacks of New York during spring 2015, 2016, and 2017 and compared with results from analogous tests done between 1980 and 2003 in many of the same streams to assess temporal changes in toxicity and inorganic monomeric aluminum (Ali) concentrations, and the role of Ali‐exposure duration on brook trout survival. Ali concentrations of 2 and 4 µmol L‐1 corresponded to low‐to‐moderate and high mortality thresholds, but prolonged exposure to ≥ 1 µmol Ali L‐1 also produced mortality. The variability, mean, and highest Ali concentrations in Buck Creek year‐round, and in several other streams during spring, decreased significantly over the past three decades. Logistic models indicate that Ali surpassed highly toxic concentrations in Buck Creek for 3‐to‐4 months annually during 2001‐03 and for 2‐to‐3 weeks annually during 2015‐17. The loss of extremely high Ali episodes indicates toxicity has declined markedly between 1989‐90, 2001‐03, and 2015‐17 test periods, yet concentrations can still cause moderate‐to‐high and complete (100%) mortality. The logistic models illustrate how mortality of brook trout in several Adirondack streams likely decreased in response to the 1990 Amendments to the Clean Air Act (which decreased acidity, Ali concentrations, and duration of toxic episodes) and offer a means to predict how changes in U.S. regulations that limit emissions of NOx and SOx (and N and S deposition loads) could affect fish survival and stream ecosystems in this region and across the Northeast.

Persistent organic pollutants reach aquatic ecosystems during application and can bioconcentrate/biomagnificate due to their lipophilic nature. Toxicological studies focus almost exclusively on the active ingredients (AIs) of pesticides, instead of commercial formulations (CFs), whose toxicity can differ due to non‐specified ingredients. The intensive use of endosulfan (ES) as a wide range insecticide over the last few decades make it one of the most frequently detected contaminants in the aquatic environment, even after it has been restricted worldwide. The aim of the present study was to evaluate the bioaccumulation and organ distribution of waterborne ES in the freshwater fish Cichlasoma dimerus, comparing between the AI and a CF. Males were exposed to 0.7 μg/L ES for two weeks. ES was quantified (GC‐ECD) in liver, testes, gills, brain and muscle. Results suggest rapid metabolism of α‐ES and β‐ES isomers to ES sulfate (ES‐S) in tissues. Isomers levels were highest in gills, indicative of recent uptake. ES‐S levels were highest in liver and testes for the AI, and testes and brain for the CF. For the AI, ES‐S levels showed a positive correlation with organ‐lipid %. No correlation was evident for CF indicating that the presence of adjuvants alters ES distribution, as gills and liver showed a higher uptake and mobilization of β‐ES. These differences in organ distribution may alter tissue‐specific toxicity, therefore additives cannot be considered inactive even if non‐toxic.

Widespread use of pesticides has resulted in the accumulation of pesticide residues in the environment due to their persistence and stability. To reduce potential exposures, we have developed broad‐acting clay‐based sorbents that can be included in the diet as enterosorbents to reduce the bioavailability and toxicity of chemicals. In this study, parent and acid‐processed calcium montmorillonite clays (CM and APM, respectively) were used to determine their potential as sorbents of the organochlorine insecticide dieldrin. We used adsorption isotherms, thermodynamics and dosimetry studies to determine the capacities and affinities of the clays, enthalpies of the binding reactions and potential doses of sorbent that could protect against high exposures. Adsorption isotherms for APM fit a Langmuir model with high enthalpy (suggesting chemisorption) and high capacity (Qmax value equal to 0.45 mol kg‐1), indicating tight binding of dieldrin. Cultures of Hydra vulgaris were used to determine the ability of sorbents to protect a living organism from dieldrin toxicity. The inclusion of acid‐processed clays resulted in the highest reduction of dieldrin toxicity (70%) in the hydra. Further work indicated that both CM and APM can significantly reduce the bioavailability of dieldrin from soil (p≤0.01). These results suggest that APM (and similar clays) can be effective sorbents of dieldrin and may be included in the diet and/or soil to protect against environmental exposures.

The toxicokinetics of triphenyl phosphate (TPHP) in vivo including the uptake, deposition and biotransformation into the metabolite diphenyl phosphate (DPHP) is presently reported in embryonated eggs and chicks of Japanese quail. Quail were dosed with TPHP at three concentrations by air cell egg‐injection on embryonic day zero followed by daily oral dosing after chicks hatched (5 days (d)). Vehicle‐only exposed controls were also used. In dosed eggs, only 33 % of the TPHP remained 2 d after injection (no hepatic development); after 10 d (post‐hepatogenesis) only 2% remained. The estimated TPHP half‐lives in the eggs ranged from 1.1 to 1.8 days for the three dosed groups. DPHP in all exposed eggs and chicks and significantly increased with dose (0.001 < p < 0.044). DPHP appears to be an important metabolite in the quail, making up 41‐74 % of all metabolites formed in embryonated eggs. In chicks, at medium‐ and high‐doses, DPHP concentrations significantly exceeded those of TPHP (p ≤ 0.007), making up 67 % and 76 % of the total burden, respectively. Our findings suggest that rapid TPHP metabolism occurred in chicks and embryonated quail eggs but may vary with the age of the embryonated egg and the stage of embryo development, which should be considered when evaluating concentrations of TPHP and DPHP measured in eggs of wild bird.

The oribatid soil mite Oppia nitens C.L. Koch, 1836, is a model microarthropod in soil ecotoxicity testing. This species has a significant role in supporting soil functions and as a suitable indicator of soil contamination. Despite its significance to the environment and to ecotoxicology, however, very little is known of its biology, ecology, and suborganismal responses to contaminants in the soil. In the present review, we present detailed and critical insights into the biology and ecology of O. nitens in relation to traits that are crucial to its adaptive responses to contaminants in soil. We used a species sensitivity distribution model to rank the species sensitivity to heavy metals (cadmium and zinc) and neonicotinoids (imidacloprid and thiacloprid) compared with other standardized soil invertebrates. Although the International Organization for Standardization and Environment and Climate Change Canada are currently standardizing a protocol for the use of O. nitens in soil toxicity testing, we believe that O. nitens is limited as a model soil invertebrate until the molecular pathways associated with its response to contaminants are better understood. These pathways can only be elucidated with information from the mites’ genome or transcriptome, which is currently lacking. Despite this limitation, we propose a possible molecular pathway to metal tolerance and a putative adverse outcome pathway to heavy metal toxicity in O. nitens. Environ Toxicol Chem 2019;38:2593–2613. © 2019 SETAC