Sensitivity of early life stages of white sturgeon, rainbow trout, and fathead minnow to copper

Toxicity prediction and risk assessment of per- and polyfluoroalkyl substances for threatened and endangered fishes

Per- and polyfluoroalkyl substances (PFASs) are severely polluted in aquatic environments and can harm aquatic organisms. Due to the limitation of conducting toxicity experiments directly on threatened and endangered (T&E) species, their toxicity data is scarce, hindering accurate risk assessments. The development of computational toxicology makes it possible to assess the risk of pollutants to T&E fishes. This study innovatively combined machine learning models, including random forest (RF), artificial neural network (ANN), and XGBoost, and the QSAR-ICE model to predict chronic developmental toxicity data of PFASs to T&E fishes. Among these, the XGBoost model exhibited superior performance, with R2 of 0.95 and 0.81 for the training and testing sets, respectively. Internal and external validation further confirmed that the XGBoost model is robust and reliable. Subsequently, it was used to predict chronic developmental toxicity data for seven priority PFASs to T&E fishes in the Yangtze River. Acipenseridae fishes (e.g., Acipenser dabryanus and Acipenser sinensis) showed high sensitivity to PFASs, possibly due to their unique lifestyle and physiological characteristics. Based on these data, the predicted no-effect concentration (PNEC) of individual PFASs was calculated, and the risk for T&E fishes in the Yangtze River was assessed. The results indicated that the risk of PFASs to T&E fishes is low (3.85 × 10-9∼8.20 × 10-4), with perfluorohexanoic acid (PFHxA) and perfluorooctanoic acid (PFOA) as the high-risk pollutants. The risk in the middle and lower reaches of the river is higher than in the upper reaches. This study provides a new approach for obtaining chronic toxicity data and conducting risk assessments for T&E species, advancing the protection of T&E species worldwide.

Toxicity of common biocides used in aquaculture to embryos and larvae of Brachymystax tsinlingensis Li

Brachymystax tsinlingensis Li is a threatened fish species endemic to China. With the problems of environmental factors and seeding breeding diseases, it is important to further improve the efficiency of seeding breeding and the basis of resource protection. This study investigated the acute toxicity of copper, zinc and methylene blue (MB) on hatching, survival, morphology, heart rate (HR) and stress behaviour of B. tsinlingensis. Eggs (diameter: 3.86 ± 0.07 mm, weight: 0.032 ± 0.004 g) of B. tsinlingensis were selected randomly from artificial propagation and developed from eye-pigmentation-stage embryos to yolk-sac stage larvae (length: 12.40 ± 0.02 mm, weight: 0.03 ± 0.001 g) and exposed to different concentrations of Cu, Zn and MB for 144 h in a series of semi-static toxicity tests. The acute toxicity tests indicated that the 96-h median lethal concentration (LC50 ) values of the embryos and larvae were 1.71 and 0.22 mg l-1 for copper and 2.57 and 2.72 mg l-1 for zinc, respectively, whereas the MB LC50 after 144-h exposure for embryos and larvae were 67.88 and 17.81 mg l-1 , respectively. The safe concentrations of copper, zinc and MB were 0.17, 0.77 and 6.79 mg l-1 for embryos and 0.03, 0.03 and 1.78 mg l-1 for larvae, respectively. Copper, zinc and MB treatments with concentrations greater than 1.60, 2.00 and 60.00 mg l-1 , respectively, led to a significantly low hatching rate and significantly high embryo mortality (P < 0.05), and copper and MB treatments with concentrations greater than 0.2 and 20 mg l-1 led to significantly high larvae mortality (P < 0.05). Exposure to copper, zinc and MB resulted in developmental defects, including spinal curvature, tail deformity, vascular system anomalies and discolouration. Moreover, copper exposure significantly reduced the HR of larvae (P < 0.05). The embryos exhibited an obvious change in behaviour, converting from the normal behaviour of emerging from the membrane head first to emerging tail first, with probabilities of 34.82%, 14.81% and 49.07% under copper, zinc and MB treatments, respectively. The results demonstrated that the sensitivity of yolk-sac larvae to copper and MB was significantly higher than that of embryos (P < 0.05) and that B. tsinlingensis embryos or larvae might be more resistant to copper, zinc and MB than other members of the Salmonidae family, which benefits their resource protection and restoration.

Impact evaluation of marking Salmo trutta with Alizarin Red S produced by different manufacturers

Fish otolith marking with the alizarin dye is a commonly used tool in sustainable fishery management. However, the reported effects of this dye on fish health are rather controversial and are possibly linked to differences in the composition of different brands of Alizarin red S (ARS). Laboratory experiments designed to elucidate effects of different concentrations of theoretically the same ARS as indicated by the CAS (Chemical Abstracts Service) number on fish at different development stages were carried out. The acute toxicity of ARS to Salmo trutta was found to be concentration- and fish developmental stage-dependant. Our study results showed that S. trutta sensitivity to ARS varies depending on its developmental stages as follows: fry (50-days after hatching) > alevins (30-days after hatching) > alevins (1-day after hatching). One of the tested ARS brands (purchased from VWR International LLC (Matsonford Road, USA)) was found to be several times more toxic to fish than another (purchased from Sigma-Aldrich (St. Louis, USA)), although according to the certificates of analysis, the tested substances were identical. Survival and growth of the S. trutta fry, which was marked with different ARS brands and stocked in the same natural stream, was investigated for two consecutive years. The results obtained indicate remarkable differences (p < 0.05) in the effects produced by the tested ARS brands, thus confirming our laboratory findings. The performed elemental analysis of the tested ARS dyes revealed significant differences in chemical impurities that these dyes contain. This study has, for the first time, expressed concern about the probable long-term impact of some ARS brands on the marked fish and their potential to bias the results of the studies dealing with ARS-marked fish.

Toxicokinetic Models for Bioconcentration of Organic Contaminants in Two Life Stages of White Sturgeon (Acipenser transmontanus)

The white sturgeon (Acipenser transmontanus) is an endangered ancient fish species that is known to be particularly sensitive to certain environmental contaminants, partly because of the uptake and subsequent toxicity of lipophilic pollutants prone to bioconcentration as a result of their high lipid content. To better understand the bioconcentration of organic contaminants in this species, toxicokinetic (TK) models were developed for the embryo-larval and subadult life stages. The embryo-larval model was designed as a one-compartment model and validated using whole-body measurements of benzo[a]pyrene (B[a]P) metabolites from a waterborne exposure to B[a]P. A physiologically based TK (PBTK) model was used for the subadult model. The predictive power of the subadult model was validated with an experimental data set of four chemicals. Results showed that the TK models could accurately predict the bioconcentration of organic contaminants for both life stages of white sturgeon within 1 order of magnitude of measured values. These models provide a tool to better understand the impact of environmental contaminants on the health and the survival of endangered white sturgeon populations.

Differences in the subcellular distribution of cadmium and copper in the gills and liver of white sturgeon (Acipenser transmontanus) and rainbow trout (Oncorhynchus mykiss)

Recent studies have shown that white sturgeon (Acipenser transmontanus) are more resistant to cadmium (Cd) compared to rainbow trout (Oncorhynchus mykiss), whereas they are more sensitive than rainbow trout when exposed to copper (Cu). Differences in the subcellular distribution of metals among species could be one of the factors responsible for the differences in the sensitivity to metals. Although, subcellular distribution has been studied extensively in many species with many metals, its direct role in species-specific differences in the sensitivity has not been well studied. The objective of this study was to evaluate the role of subcellular distribution of metals in species-specific differences in the sensitivity to metals between sturgeon and trout. We compared the subcellular distribution of metals Cd and Cu in the cellular debris, heat-stable proteins, heat-denatured fraction, metal-rich granules, and organelles fractions from the gills and liver after exposure of juveniles of both species to 1.25 and 20 μg/L Cd and Cu for 8 days, respectively. Sturgeon diverted a higher amount of Cd towards biologically inactive metal pool (BIM) and a lower amount towards the biologically active metal pool (BAM) compared to trout in both tissues. This explained why sturgeon are able to tolerate a relatively higher exposure level to Cd compared to trout. For Cu, there was no statistically significant species-specific differences in the amounts diverted towards either BAM or BIM; hence, white sturgeon's greater sensitivity to Cu was not explained by its subcellular distribution strategies.

Comparing Trace Elements (As, Cu, Ni, Pb, and Zn) in Soils and Surface Waters among Montane, Upland Watersheds and Lowland, Urban Watersheds in New England, USA

Trace element biogeochemistry from soils to rivers is important for toxicity to aquatic ecosystems. The objective of this study was to determine whether trace element exports in contrasting watersheds are controlled by their abundance in soil, current land uses in the watershed, or geologic processes. Upland soils and river water samples were collected throughout the Deerfield watershed in southern Vermont and western Massachusetts and in the Quinebaug and Shetucket watersheds of eastern Connecticut. Soil concentrations were only an important predictor for dissolved Fe export, but no other trace element. Soil pH was not correlated with normalized dissolved exports of trace elements, but DOC was correlated with normalized dissolved Pb and Ni exports. The limited spatial and depth of soil sampling may have contributed to the poor correlation. Surprisingly, linear regressions and principal component analysis showed that human development was associated with higher soil trace metal concentrations but not significantly correlated with dissolved trace elements export. Instead, forest abundance was a strong predictor for lower Cu, Pb, and Zn soil concentrations and lower As, Fe, Ni and Pb dissolved exports across the watersheds. Dissolved exports of Al, K, and Si suggest that enhanced mineral dissolution in the montane watersheds was likely an important factor for matching or exceeding normalized pollutant trace element exports in more urbanized watersheds. Further studies are needed to evaluate subsurface/hyporheic controls as well as soil–surface water interface to quantify exchange and transport.

Comparative analyses of oxidative stress response and metallothionein induction in white sturgeon and rainbow trout during acute waterborne copper exposure

Early life-stages of the endangered white sturgeon (Acipenser transmontanus) have been shown to be among the most sensitive fishes to aqueous copper (Cu) exposure. In a recent analogous study, we examined the role of whole-body Cu accumulation and Na homeostasis in species-specific differences between the sensitivity of white sturgeon and a common laboratory fish model, rainbow trout, to Cu. However, the potential roles of important mechanisms such as Cu-induced oxidative stress and/or metallothionein (MT) induction as potential drivers of sensitivity of white sturgeon to Cu have not been investigated to date. Here, rainbow trout and white sturgeon from three different early life-stages were exposed to waterborne Cu for 96 h, following which major antioxidant parameters, lipid peroxidation and MT gene expression were evaluated. Results indicated that during larval and swim-up life-stages, Cu induced oxidative damage in white sturgeon was greater than in rainbow trout. Moreover, baseline glutathione (GSH) was significantly greater in rainbow trout than white sturgeon. Observations also suggested that trout exceedingly relied on GSH to combat Cu-induced oxidative stress as they grew older. In contrast, sturgeon recruited an increasing level of MT to neutralize Cu-induced oxidative stress and/or Cu loading. In our recent study, we demonstrated that Na homeostasis is more susceptible to Cu in white sturgeon than in rainbow trout. Collectively, these findings indicate that the greater degree of oxidative damage in early life-stages, in addition to the higher magnitude of the disruption of Na homeostasis, contributes to the higher sensitivity of white sturgeon to Cu exposure.

Metals and PFAS in stormwater and surface runoff in a semi-arid Canadian city subject to large variations in temperature among seasons

Because compounds accumulate through dry periods and enter aquatic systems in just a few seasonal events such as snowmelt and summer storms, surface waters in semi-arid, cold regions, such as the Canadian Prairies, are particularly vulnerable to loading of contaminant from runoff events from surfaces. This study assessed concentrations of metals and selected trace organics entering a river via surface runoff from an urban region and how these semi-arid regions with large seasonal variations in temperature might differ from more temperate regions. Selected potentially harmful elements (PHEs) including, Mn with Cr, Cu, Zn, Ba and U all exceeded guideline discharge values set by the Canadian Council of the Ministers of the Environment (CCME) by as much as 16-fold. Variation among discharges during spring, summer and winter was observed. For example, across the whole city, an estimated 6 kg of zinc was discharged in a spring storm, 36 kg in a summer storm and 17 tonnes in snowmelt. The mass of Zn discharged is similar to the annual loading estimated for Stockholm, Sweden, but in Saskatoon, Saskatchewan, Canada, the bulk of runoff was during snowmelt. The mean sum of poly- and per-fluoroalkyl substances (PFAS) in stormwater was 9.0 ng L^-1, which is consistent with concentrations observed in other Canadian cities (6.5-16 ng L^-1). These concentrations of PFAS are likely due to dispersed sources and orders of magnitude less than thresholds for toxicity to fish and aquatic invertebrates.

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.

Influence of Dissolved Organic Carbon on the Acute Toxicity of Copper and Zinc to White Sturgeon (Acipenser transmontanus) and a Cladoceran (Ceriodaphnia dubia)

We conducted acute lethality tests with white sturgeon (Acipenser transmontanus) and Ceriodaphnia dubia exposed to copper and zinc at dissolved organic carbon concentrations ranging from 0.5 to 5.5 mg/L. Dissolved organic carbon had minimal effects on zinc toxicity but did have a protective effect on acute copper toxicity, which was equal to that predicted by the copper biotic ligand model (BLM). The BLM-adjusted copper median effect concentrations for A. transmontanus ranged from 2.4 to 8.2 mg/L. Environ Toxicol Chem 2019;38:2682-2687. Published 2019 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.

In Silico Site-Directed Mutagenesis Informs Species-Specific Predictions of Chemical Susceptibility Derived From the Sequence Alignment to Predict Across Species Susceptibility (SeqAPASS) Tool

Chemical hazard assessment requires extrapolation of information from model organisms to all species of concern. The Sequence Alignment to Predict Across Species Susceptibility (SeqAPASS) tool was developed as a rapid, cost-effective method to aid cross-species extrapolation of susceptibility to chemicals acting on specific protein targets through evaluation of protein structural similarities and differences. The greatest resolution for extrapolation of chemical susceptibility across species involves comparisons of individual amino acid residues at key positions involved in protein-chemical interactions. However, a lack of understanding of whether specific amino acid substitutions among species at key positions in proteins affect interaction with chemicals made manual interpretation of alignments time consuming and potentially inconsistent. Therefore, this study used in silico site-directed mutagenesis coupled with docking simulations of computational models for acetylcholinesterase (AChE) and ecdysone receptor (EcR) to investigate how specific amino acid substitutions impact protein-chemical interaction. This study found that computationally derived substitutions in identities of key amino acids caused no change in protein-chemical interaction if residues share the same side chain functional properties and have comparable molecular dimensions, while differences in these characteristics can change protein-chemical interaction. These findings were considered in the development of capabilities for automatically generated species-specific predictions of chemical susceptibility in SeqAPASS. These predictions for AChE and EcR were shown to agree with SeqAPASS predictions comparing the primary sequence and functional domain sequence of proteins for more than 90% of the investigated species, but also identified dramatic species-specific differences in chemical susceptibility that align with results from standard toxicity tests. These results provide a compelling line of evidence for use of SeqAPASS in deriving screening level, species-specific, susceptibility predictions across broad taxonomic groups for application to human and ecological hazard assessment.

Sensitivity of white sturgeon and rainbow trout to waterborne copper exposure: A comparative study of copper-induced disruption of sodium homeostasis

Recent studies have demonstrated that white sturgeon are more sensitive to acute exposure to Cu than rainbow trout (Oncorhynchus mykiss), especially during early life-stages. However, the physiological mechanisms underlying this difference in sensitivity to Cu is not known. In the present study, we first confirmed the higher sensitivity (lower 96 h LC₅₀ values) of white sturgeon to Cu at three different life stages (larva, swim-up, and juvenile) relative to their counterparts in rainbow trout. We also demonstrated that acute exposure to Cu (50 μg/L for 4.5 h) caused a significantly greater reduction in the rate of waterborne Na uptake in white sturgeon relative to that in rainbow trout across all three life-stages. In agreement with this observation, we also found that acute exposure to Cu (20 μg/L for 48 h) elicits a significantly greater decrease in whole body Na level in all life stages of white sturgeon compared to rainbow trout. In contrast, white sturgeon demonstrated a higher or similar level of Cu body burden relative to rainbow trout during acute Cu exposure (20 μg/L for 24 h), thereby indicating that Cu bioaccumulation is not a good indicator of its toxicity in these species. Overall, our study demonstrated that the differences in sensitivity to acute Cu exposure between white sturgeon and rainbow trout can be explained on the basis of differential effects of Cu on Na homeostasis.

Integrating physiological data with the conservation and management of fishes: a meta-analytical review using the threatened green sturgeon (Acipenser medirostris)

Reversing global declines in the abundance and diversity of fishes is dependent on science-based conservation solutions. A wealth of data exist on the ecophysiological constraints of many fishes, but much of this information is underutilized in recovery plans due to a lack of synthesis. Here, we used the imperiled green sturgeon (Acipenser medirostris) as an example of how a quantitative synthesis of physiological data can inform conservation plans, identify knowledge gaps and direct future research actions. We reviewed and extracted metadata from peer-reviewed papers on green sturgeon. A total of 105 publications were identified, spanning multiple disciplines, with the primary focus being conservation physiology (23.8%). A meta-analytical approach was chosen to summarize the mean effects of prominent stressors (elevated temperatures, salinity, low food availability and contaminants) on several physiological traits (growth, thermal tolerance, swimming performance and heat shock protein expression). All examined stressors significantly impaired green sturgeon growth, and additional stressor-specific costs were documented. These findings were then used to suggest several management actions, such as mitigating salt intrusion in nursery habitats and maintaining water temperatures within optimal ranges during peak spawning periods. Key data gaps were also identified; research efforts have been biased towards juvenile (38.1%) and adult (35.2%) life-history stages, and less data are available for early life-history stages (embryonic, 11.4%; yolk-sac larvae, 12.4%; and post yolk-sac larvae, 16.2%). Similarly, most data were collected from single-stressor studies (91.4%) and there is an urgent need to understand interactions among stressors as anthropogenic change is multi-variate and dynamic. Collectively, these findings provide an example of how meta-analytic reviews are a powerful tool to inform management actions, with the end goal of maximizing conservation gains from research efforts.

Sub-lethal effects of waterborne copper in early developmental stages of rainbow trout (Oncorhynchus mykiss)

The aim of this work was to study the impact of copper during a sub-chronic exposure to environmental concentrations in the early life stages of rainbow trout (Oncorhynchus mykiss). Eyed-stage embryos of rainbow trout, at 265 °D, were exposed in semi-static conditions to sub-lethal concentrations of CuSO₄ up to the larval stage (528 °D) under laboratory-controlled conditions. During 3 weeks, they were exposed to the environmentally-realistic concentration of 2 µg/L Cu and to a 10-fold higher concentration, 20 µg/L Cu. Several biological (survival, hatching success, malformation, growth) and behavioral (swimming activity) and molecular endpoints (genotoxicity and gene transcription) were studied. Exposure to 20 µg/L Cu had an inhibitory effect on hatching and increased half-hatched embryos (25%). At the end of the exposure, no significant differences were observed in growth of the larvae exposed to the highest Cu concentration. However, larvae exposed to 2 µg/L Cu exhibited increased growth in comparison with non-exposed larvae. The percentage of malformed larvae was significantly higher for both copper conditions, with skeletal malformations being the most observed. Expression of several genes was evaluated in whole larvae using quantitative real-time PCR. Genes involved in detoxification (gst, mt1 and mt2) and in cell cycle arrest (p53) were significantly repressed in both copper conditions when compared to control. In addition, potential genotoxic effects on larvae were investigated by the comet assay on blood cells, but this test did not demonstrate any significant DNA damage on larvae exposed to copper. This study confirms the adverse effects of copper on early life stages of rainbow trout even at the lowest environmentally relevant tested concentration.

Behavioral effects of copper on larval white sturgeon

Early-life stage white sturgeon are sensitive to copper (Cu), with adverse behavioral responses observed during previous studies. The objectives of the present study were to quantify the effects of Cu exposure on white sturgeon swimming and feeding behaviors and determine their time to response. Larval sturgeon (1-2, 28, or 35 d posthatch [dph]) were exposed to Cu (0.5-8 μg/L) for 4 to 14 d. Abnormal behavioral changes were observed within the first few days of exposure including loss of equilibrium and immobilization. Digital video tracking software revealed decreased swimming activity with increasing Cu concentration. Significant changes in behavior and mortality occurred at concentrations of Cu between 1 and 8 μg/L. Juvenile white sturgeon, 58 dph, exposed to 12 μg/L Cu consumed 37 to 60% less food than controls after 3 d of exposure. The present results indicate that behavioral endpoints were more sensitive than some standard toxicity test endpoints and can effectively expand the sensitivity of standard toxicity tests for white sturgeon. Swimming behavior was impaired to the extent that survival in the field would likely be jeopardized. Such data would provide managers a useful metric for characterizing the risks of Cu contamination to white sturgeon. Environ Toxicol Chem 2019;38:132-144. 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.

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.

Nitrate: An Environmental Endocrine Disruptor? A Review of Evidence and Research Needs

Nitrate is heavily used as an agricultural fertilizer and is today a ubiquitous environmental pollutant. Environmental endocrine effects caused by nitrate have received increasing attention over the last 15 years. Nitrate is hypothesized to interfere with thyroid and steroid hormone homeostasis and developmental and reproductive end points. The current review focuses on aquatic ecotoxicology with emphasis on field and laboratory controlled in vitro and in vivo studies. Furthermore, nitrate is just one of several forms of nitrogen that is present in the environment and many of these are quickly interconvertible. Therefore, the focus is additionally confined to the oxidized nitrogen species (nitrate, nitrite and nitric oxide). We reviewed 26 environmental toxicology studies and our main findings are (1) nitrate has endocrine disrupting properties and hypotheses for mechanisms exist, which warrants for further investigations; (2) there are issues determining actual nitrate-speciation and abundance is not quantified in a number of studies, making links to speciation-specific effects difficult; and (3) more advanced analytical chemistry methodologies are needed both for exposure assessment and in the determination of endocrine biomarkers.

Experimentally derived acute and chronic copper Biotic Ligand Models for rainbow trout

We evaluated the effects of varying water chemistry ([Ca²⁺]=0.2-3mM, [Mg²⁺]=0.05-3mM, dissolved organic matter (DOM, natural, from maple leaves)=0.3-10mg of CL^-1, pH=5.0-8.5) on the acute (96-h, unfed fish) and chronic (30-d, fed fish) toxicity of waterborne Cu to juvenile rainbow trout (Oncorhynchus mykiss) exposed in flow-through conditions. Acute and chronic Biotic Ligand Models (BLMs) were developed from the obtained toxicity data-sets, using the Visual MINTEQ software. Our results indicate that Cu is predominantly an acute toxicant to rainbow trout, as there were no observable growth effects and the 96-h and 30-d LC50 values were similar, with mortality mostly occurring within the first few days of exposure. Calcium and DOM were greatly protective against both acute and chronic Cu toxicity, but Mg seemed to only protect against chronic toxicity. Additional protection by pH 5.0 in acute exposure and by pH 8.5 in chronic exposure occurred. In the range of conditions tested, the observed 96-h LC50 and 30-d LC20 values varied by a factor of 39 and 27 respectively. The newly developed acute and chronic BLMs explained these variations reasonably well (i.e. within a 2-fold error), except at pH≥8 where the high observed acute toxicity could not be explained, even by considering an equal contribution of CuOH⁺ and Cu²⁺ to the overall Cu toxicity. The 96-h LC50 values of 59% of 90 toxicity tests from 19 independent studies in the literature were reasonably well predicted by the new acute BLM. The LC20 predictions from the new chronic BLM were reasonable for 7 out of 14 toxicity tests from 6 independent chronic studies (with variable exposure durations). The observed deviations from BLM predictions may be due to uncertainties in the water chemistry in these literature studies and/or to differences in fish sensitivity. A residual pH effect was also observed for both the acute and the chronic data-sets, as the ratio of predicted vs. observed LC values generally increased with the pH. Additional mechanistic studies are required to understand the influence of pH, Na, and Mg on Cu toxicity to trout. The present study presents the first experimentally developed chronic Cu BLM for the rainbow trout. To the best of our knowledge, it also presents the first acute Cu BLM that is based on a published data-set for trout. These newly developed BLMs should contribute to improving the risk assessment of Cu to fish in freshwater.

A cell-free testing platform to screen chemicals of potential neurotoxic concern across twenty vertebrate species

There is global demand for new in vitro testing tools for ecological risk assessment. The objective of the present study was to apply a set of cell-free neurochemical assays to screen many chemicals across many species in a relatively high-throughput manner. The platform assessed 7 receptors and enzymes that mediate neurotransmission of γ-aminobutyric acid, dopamine, glutamate, and acetylcholine. Each assay was optimized to work across 20 vertebrate species (5 fish, 5 birds, 7 mammalian wildlife, 3 biomedical species including humans). We tested the screening assay platform against 80 chemicals (23 pharmaceuticals and personal care products, 20 metal[loid]s, 22 polycyclic aromatic hydrocarbons and halogenated organic compounds, 15 pesticides). In total, 10 800 species-chemical-assay combinations were tested, and significant differences were found in 4041 cases. All 7 assays were significantly affected by at least one chemical in each species tested. Among the 80 chemicals tested, nearly all resulted in a significant impact on at least one species and one assay. The 5 most active chemicals were prochloraz, HgCl₂ , Sn, benzo[a]pyrene, and vinclozolin. Clustering analyses revealed groupings according to chemicals, species, and chemical-assay combinations. The results show that cell-free assays can screen a large number of samples in a short period of time in a cost-effective manner in a range of animals not easily studied using traditional approaches. Strengths and limitations of this approach are discussed, as well as next steps. Environ Toxicol Chem 2017;36:3081-3090. © 2017 SETAC.

Expression stability and selection of optimal reference genes for gene expression normalization in early life stage rainbow trout exposed to cadmium and copper

Gene expression analysis represents a powerful approach to characterize the specific mechanisms by which contaminants interact with organisms. One of the key considerations when conducting gene expression analyses using quantitative real-time reverse transcription-polymerase chain reaction (qPCR) is the selection of appropriate reference genes, which is often overlooked. Specifically, to reach meaningful conclusions when using relative quantification approaches, expression levels of reference genes must be highly stable and cannot vary as a function of experimental conditions. However, to date, information on the stability of commonly used reference genes across developmental stages, tissues and after exposure to contaminants such as metals is lacking for many vertebrate species including teleost fish. Therefore, in this study, we assessed the stability of expression of 8 reference gene candidates in the gills and skin of three different early life-stages of rainbow trout after acute exposure (24h) to two metals, cadmium (Cd) and copper (Cu) using qPCR. Candidate housekeeping genes were: beta actin (b-actin), DNA directed RNA polymerase II subunit I (DRP2), elongation factor-1 alpha (EF1a), glyceraldehyde 3-phosphate dehydrogenase (GAPDH), glucose-6-phosphate dehydrogenase (G6PD), hypoxanthine phosphoribosyltransferase (HPRT), ribosomal protein L8 (RPL8), and 18S ribosomal RNA (18S). Four algorithms, geNorm, NormFinder, BestKeeper, and the comparative ΔCt method were employed to systematically evaluate the expression stability of these candidate genes under control and exposed conditions as well as across three different life-stages. Finally, stability of genes was ranked by taking geometric means of the ranks established by the different methods. Stability of reference genes was ranked in the following order (from lower to higher stability): HPRT<GAPDH<EF1a<G6PD<RPL8<DRP2<b-actin in gills of fish exposed to Cd; b-actin<GAPDH<G6PD<DRP2<RPL8<HPRT<EF1a in gills of fish exposed to Cu; RPL8<HPRT<GAPDH<G6PD<EF1a<DRP2<b-actin in the skin of fish exposed to Cd; and EF1a<GAPDH<RPL8<HPRT<G6PD<b-actin<DRP2 in the skin of fish exposed to Cu. The results demonstrated that the stability of reference genes depended on the metal, life-stage and/or organ in question. Thus, attention should be paid to these factors before selection of reference gene for relative quantification of the gene expressions.

Effects of chronic exposure to dietary selenomethionine on the physiological stress response in juvenile white sturgeon (Acipenser transmontanus)

Selenium (Se) is an essential micronutrient, but at low concentrations can be toxic to aquatic organisms. Selenomethionine (SeMeth) is the primary dietary form of Se aquatic organisms are exposed to and is an environmental concern because it persists and bioaccumulates. White sturgeon (WS) might be particularly susceptible to bioaccumulative toxicants, such as SeMeth, due to their longevity and benthic lifestyle. Se exposure is known to have adverse effects on the physiological stress response in teleosts, but these effects are unknown in WS. Therefore, the goal of this study was to determine effects of dietary SeMeth on the ability of WS to mount a stress response. Juvenile WS were administered food spiked with 1.4, 5.6, 22.4 and 104.4μg Se/g dry mass (dm) for 72days. Lower doses were chosen to represent environmentally relevant concentrations, while the high dose represented a worst case scenario exposure. On day 72, fish were subjected to a 2min handling stressor, and they were sampled at 0, 2 and 24h post-stressor. Cortisol, glucose and lactate concentrations were quantified in blood plasma and glycogen concentrations were quantified in muscle and liver. Transcript abundance of genes involved in corticosteroidogenesis and energy metabolism were determined using qPCR. Under basal conditions, WS fed 104.4μg Se/g dm had significantly greater concentrations of plasma cortisol and lactate, and significantly lower concentrations of plasma glucose and liver glycogen, compared to controls. Corticosteroid 11-beta dehydrogenase 2 (hsd11b2) abundance was lower in WS fed 22.4 and 104.4μg Se/g dm, indicating less conversion of cortisol to cortisone. Abundance of the glucocorticoid receptor (gcr) was significantly lower in high dose WS, suggesting lower tissue sensitivity to glucocorticoids. The increasing trend in phosphoenolpyruvate carboxykinase (pepck) abundance, with increasing SeMeth exposure, was consistent with greater cortisol and glucose concentrations in high dose WS. Exposure to an acute handling stressor elicited a typical cortisol response, but the magnitude of the response appeared to be significantly lower than those typically observed in teleosts. SeMeth also did not appear to modulate the cortisol response to a secondary stressor. However, WS exposed to 22.4μg Se/g dm and sampled 2h post-stressor, had significantly higher concentrations of muscle glycogen compared to controls, indicating effects on their ability to utilize muscle glycogen for energy. Overall, the results indicate that chronic exposure to dietary SeMeth concentrations >22.4μg/g can affect cortisol dynamics and mobilization of energy substrates in juvenile WS.

Is hepatic oxidative stress a main driver of dietary selenium toxicity in white sturgeon (Acipenser transmontanus)?

Most species of sturgeon have experienced significant population declines and poor recruitment over the past decades, leading many, including white sturgeon (Acipenser transmontanus), to be listed as endangered. Reasons for these declines are not yet fully understood but benthic lifestyle, longevity, and delayed sexual maturation likely render sturgeon particularly susceptible to factors such as habitat alteration and contaminant exposures. One contaminant of particular concern to white sturgeon is selenium (Se), especially in its more bioavailable form selenomethionine (SeMet), as it is known to efficiently bioaccumulate in prey items of this species. Studies have shown white sturgeon to be among the most sensitive species of fish to dietary SeMet as well as other pollutants such as metals, dioxin-like chemicals and endocrine disrupters. One of the primary hypothesized mechanisms of toxicity of SeMet in fish is oxidative stress; however, little is know about the specific mode by which SeMet affects the health of white sturgeon. Therefore, the aim of this study was to characterize oxidative stress and associated antioxidant responses as a molecular event of toxicity, and to link it with the pathological effects observed previously. Specifically, three-year-old white sturgeon were exposed for 72 days via their diet to 1.4, 5.6, 22.4 or 104.4µg Se per g feed (dm). Doses were chosen to range over a necessary Se intake level, current environmentally relevant intakes and an intake representing predicted increases of Se release. Lipid hydroperoxides, which are end products of lipid oxidation, were quantified as a marker of oxidative stress. Changes in gene expression of glutathione peroxidase (GPx), superoxide dismutase, catalase, glutathione S-transferase, apoptosis inducing factor and caspase 3 were quantified as markers of the response to oxidative stress. Concentrations of lipid hydroperoxides were highly variable within dose groups and no dose response was observed. GPx expression was significantly increased in the low dose group indicating an induced antioxidant response. Expression of other genes were not significantly induced or suppressed. Overall, there was very little evidence of oxidative stress, and therefore, in contrast to previous reports on other species of teleost fishes, oxidative stress is not believed to be a main driver of toxicity in white sturgeon exposed to SeMet.

Linking Oxidative Stress and Magnitude of Compensatory Responses with Life-Stage Specific Differences in Sensitivity of White Sturgeon (Acipenser transmontanus) to Copper or Cadmium

Sensitivity of white sturgeon (Acipenser transmontanus) to copper (Cu) or cadmium (Cd) has been shown to significantly differ as a function of life-stage. This study investigated oxidative stress, metal homeostasis, and associated compensatory responses as potential mechanisms of this sensitivity pattern in three early life-stages. Sturgeon were most sensitive to Cu at 15 days post hatch (dph), which was accompanied by a significant increase in lipid peroxidation (LPO). Genes involved with amelioration of oxidative stress were significantly less inducible at this stage than in older, less sensitive fry. At 48 dph, acute lethality of sturgeon exposed to Cd was greatest and body LPO was significantly induced by 3.5-fold at 5 μg Cd/L. Moreover, there was a small but significant increase in antioxidative responses. At 139 dph, sturgeon were most tolerant to Cu and Cd and accumulation of these metals was least. Also, expression of metallothionein (MT) and apoptotic genes were greatest while expression of metal transporters was reduced and concentration of LPO was not different from controls. Our results suggest that life-stage specific sensitivity of white sturgeon to metals is complex, encompassing differences in the ability to mount compensatory responses important for metal homeostasis and combating oxidative stress and concomitant damages.

Adverse health effects and histological changes in white sturgeon (Acipenser transmontanus) exposed to dietary selenomethionine

It has been shown that selenium (Se) released to the aquatic environment can have devastating effects on local wildlife. White sturgeon (Acipenser transmontanus) have a life history particularly susceptible to contaminants, and their protection is of interest as they are culturally and economically important, and many populations are classified as endangered. During the present 72-d dietary study, multiple signs of decreased health and Se lethality were observed. Juvenile white sturgeon were given diets containing 1.4 μg, 5.6 μg, 22.4 μg, or 104.4 μg selenomethionine/g food (dry mass). Selenium accumulated in muscle and liver tissue in a dose-dependent manner. Edema causing exophthalmos developed within 15 d and 23 d, and lethal effects occurred in 54% and 22% of fish in the high- and medium-dose groups, respectively. Growth and hepatosomatic index were significantly lower in the high-dose group, which also had a high incidence of food avoidance. Histology of the liver revealed a dose-dependent increase in melanomacrophage aggregates and decrease of energy stores, which indicated toxicity. These results indicate that white sturgeon are susceptible to the effects of Se accumulation over relatively short time periods. This stresses the need for continued sturgeon research and studies looking into the environmental fate and regulation of released Se. Environ Toxicol Chem 2016;35:1741-1750. © 2015 SETAC.

Impact of Predator Cues on Responses to Silver Nanoparticles in Daphnia carinata

The past decades have witnessed a boom in nanotechnology that has led to increasing production and application of silver nanoparticles (AgNPs) in the textile industry due to their antimicrobial properties. Increase in the manufacture and use of NPs inevitably has resulted in their increased release into aquatic environments resulting in the exposure of organisms living in these environments. Recently, the risk of exposure to NPs and the potential interaction with biological systems has received increasing attention. The present study investigated the potential effects of predator cues on the toxicity of environmentally relevant concentrations of AgNPs in Daphnia carinata at organismal and biochemical levels. The results of this study show that exposure to environmentally relevant concentrations of AgNPs can result in adverse effects on daphnids with 24- and 48-h LC50 values of 3.56 and 1.75 μg/L, respectively. Furthermore, significant inhibition of reproduction was observed at concentrations as low as 0.5 μg/L. Exposure to predator cues alone resulted in an increase in reproduction and inhibition of superoxide dismutase activity in daphnids. However, coexposure to predator cues interacted in an antagonistic manner with AgNPs with a 24-h LC50 value of 10.81 μg/L compared with 3.56 μg/L for AgNPs alone. In summary, AgNPs could pose risks to aquatic invertebrates at environmentally relevant concentrations. Interestingly, the presence of other factors, such as predator cues, moderated the effects of exposure to AgNPs. Therefore, there is a need to further investigate the potential interactions between NPs and biological factors that can modulate toxicity of NPs for application to the risk assessment of aquatic invertebrates.

Profiling DNA damage and repair capacity in sea urchin larvae and coelomocytes exposed to genotoxicants

The ability to protect the genome from harmful DNA damage is critical for maintaining genome stability and protecting against disease, including cancer. Many echinoderms, including sea urchins, are noted for the lack of neoplastic disease, but there are few studies investigating susceptibility to DNA damage and capacity for DNA repair in these animals. In this study, DNA damage was induced in adult sea urchin coelomocytes and larvae by exposure to a variety of genotoxicants [UV-C (0-3000 J/m(2)), hydrogen peroxide (0-10mM), bleomycin (0-300 µM) and methylmethanesulfonate (MMS, 0-30 mM)] and the capacity for repair was measured over a 24-h period of recovery. Larvae were more sensitive than coelomocytes, with higher levels of initial DNA damage (fast micromethod) for all genotoxicants except MMS and increased levels of mortality 24h following treatment for all genotoxicants. The larvae that survived were able to efficiently repair damage within 24-h recovery. The ability to repair DNA damage differed depending on treatments, but both larvae and coelomocytes were able to most efficiently repair H2O2-induced damage. Time profiles of expression of a panel of DNA repair genes (ddb1, ercc1, xpc, xrcc1, pcna, ogg1, parp1, parp2, ape, brca1, rad51, xrcc2, xrcc3, xrcc4, xrcc5, xrcc6 and gadd45), throughout the period of recovery, showed greater gene induction in coelomocytes compared with larvae, with particularly high expression of xrcc1, ercc1, parp2 and pcna. The heterogeneous response of larvae to DNA damage may reflect a strategy whereby a subset of the population is equipped to withstand acute genotoxic stress, while the ability of coelomocytes to resist and repair DNA damage confirm their significant role in protection against disease. Consideration of DNA repair capacity is critical for understanding effects of genotoxicants on organisms, in addition to shedding light on life strategies and disease susceptibility.

Identification and response to metals of metallothionein in two ancient fishes: white sturgeon (Acipenser transmontanus) and lake sturgeon (Acipenser fulvescens)

White sturgeon (Acipenser transmontanus) are among the most sensitive species of fishes to Cu, Cd, and Zn, but there is no information about sensitivity of lake sturgeon (Acipenser fulvescens). To begin to elucidate molecular mechanism(s) of sensitivity of sturgeons to metals a cDNA encoding metallothionein (MT) was amplified from livers of white sturgeon (WS-MT) and lake sturgeon (LS-MT), and expression in response to Cu, Cd, or Zn was characterized in liver explants from each species. The primary structure of WS-MT and LS-MT contained 20 cysteine residues, which is the same as MTs of teleost fishes. However, the primary structure of WS-MT and LS-MT contained 63 amino acids, which is longer than any MT identified in teleost fishes. Abundance of transcripts of WS-MT in explants exposed to 0.3, 3, 30, or 100 μg/L of Cu was 1.7-, 1.7-, 2.1-, and 2.6-fold less than in controls, respectively. In contrast, abundances of transcripts of WS-MT were 3.3- and 2.4-fold greater in explants exposed to 30 μg/L of Cd and 1000 μg/L of Zn, respectively. Abundance of transcripts of LS-MT was not significantly different at any concentration of Cu, Cd, or Zn. MT is hypothesized to represent a critical mechanism for detoxification of metals. Therefore, results of this study suggest that sensitivity of sturgeons to exposure to Cu, Cd, or Zn might be a result of the relatively lesser maximal response of MT to metals. The study also suggestslake sturgeon might be more sensitive than white sturgeon to metals.

Risk assessment considerations with regard to the potential impacts of pesticides on endangered species

Simple, deterministic screening-level assessments that are highly conservative by design facilitate a rapid initial screening to determine whether a pesticide active ingredient has the potential to adversely affect threatened or endangered species. If a worst-case estimate of pesticide exposure is below a very conservative effects metric (e.g., the no observed effects concentration of the most sensitive tested surrogate species) then the potential risks are considered de minimis and unlikely to jeopardize the existence of a threatened or endangered species. Thus by design, such compounded layers of conservatism are intended to minimize potential Type II errors (failure to reject a false null hypothesis of de minimus risk), but correspondingly increase Type I errors (falsely reject a null hypothesis of de minimus risk). Because of the conservatism inherent in screening-level risk assessments, higher-tier scientific information and analyses that provide additional environmental realism can be applied in cases where a potential risk has been identified. This information includes community-level effects data, environmental fate and exposure data, monitoring data, geospatial location and proximity data, species biology data, and probabilistic exposure and population models. Given that the definition of "risk" includes likelihood and magnitude of effect, higher-tier risk assessments should use probabilistic techniques that more accurately and realistically characterize risk. Moreover, where possible and appropriate, risk assessments should focus on effects at the population and community levels of organization rather than the more traditional focus on the organism level. This document provides a review of some types of higher-tier data and assessment refinements available to more accurately and realistically evaluate potential risks of pesticide use to threatened and endangered species.

Acute sensitivity of white sturgeon (Acipenser transmontanus) and rainbow trout (Oncorhynchus mykiss) to copper, cadmium, or zinc in water-only laboratory exposures

The acute toxicity of cadmium, copper, and zinc to white sturgeon (Acipenser transmontanus) and rainbow trout (Oncorhynchus mykiss) were determined for 7 developmental life stages in flow-through water-only exposures. Metal toxicity varied by species and by life stage. Rainbow trout were more sensitive to cadmium than white sturgeon across all life stages, with median effect concentrations (hardness-normalized EC50s) ranging from 1.47 µg Cd/L to 2.62 µg Cd/L with sensitivity remaining consistent during later stages of development. Rainbow trout at 46 d posthatch (dph) ranked at the 2nd percentile of a compiled database for Cd species sensitivity distribution with an EC50 of 1.46 µg Cd/L and 72 dph sturgeon ranked at the 19th percentile (EC50 of 3.02 µg Cd/L). White sturgeon were more sensitive to copper than rainbow trout in 5 of the 7 life stages tested with biotic ligand model (BLM)-normalized EC50s ranging from 1.51 µg Cu/L to 21.9 µg Cu/L. In turn, rainbow trout at 74 dph and 95 dph were more sensitive to copper than white sturgeon at 72 dph and 89 dph, indicating sturgeon become more tolerant in older life stages, whereas older trout become more sensitive to copper exposure. White sturgeon at 2 dph, 16 dph, and 30 dph ranked in the lower percentiles of a compiled database for copper species sensitivity distribution, ranking at the 3rd (2 dph), 5th (16 dph), and 10th (30 dph) percentiles. White sturgeon were more sensitive to zinc than rainbow trout for 1 out of 7 life stages tested (2 dph with an biotic ligand model-normalized EC50 of 209 µg Zn/L) and ranked in the 1st percentile of a compiled database for zinc species sensitivity distribution.

Chronic sensitivity of white sturgeon (Acipenser transmontanus) and rainbow trout (Oncorhynchus mykiss) to cadmium, copper, lead, or zinc in laboratory water-only exposures

Chronic toxicity of cadmium, copper, lead, or zinc to white sturgeon (Acipenser transmontanus) and rainbow trout (Oncorhynchus mykiss) was evaluated in water-only exposures started with newly hatched larvae or approximately 1-mo-old juveniles. The 20% effect concentration (EC20) for cadmium from the sturgeon tests was higher than the EC20 from the trout tests, whereas the EC20 for copper, lead, or zinc for the sturgeon were lower than those EC20s for the trout. When the EC20s from the present study were included in compiled toxicity databases for all freshwater species, species mean chronic value for white sturgeon was in a relatively low percentile of the species sensitivity distribution for copper (9th percentile) and in the middle percentile for cadmium (55th percentile), zinc (40th percentile), or lead (50th percentile). However, the species mean chronic value for rainbow trout was in a high percentile for copper, lead, and zinc (∼68th-82nd percentile), but in a low percentile for cadmium (23rd percentile). The trout EC20s for each of the 4 metals and the sturgeon EC20s for cadmium or lead were above US Environmental Protection Agency chronic ambient water quality criteria (AWQC) or Washington State chronic water quality standards (WQS), whereas the sturgeon EC20s for copper or zinc were approximately equal to or below the chronic AWQC and WQS. In addition, acute 50% effect concentrations (EC50s) for copper obtained in the first 4 d of the chronic sturgeon test were below the final acute value used to derive acute AWQC and below acute WQS for copper.

Identification and expression of aryl hydrocarbon receptors (AhR1 and AhR2) provide insight in an evolutionary context regarding sensitivity of white sturgeon (Acipenser transmontanus) to dioxin-like compounds

Sturgeons are ancient fishes, which are endangered in many parts of the world. Due to their benthic nature and longevity, sturgeon are at great risk of exposure to bioaccumulative contaminants such as dioxin-like compounds (DLCs). Despite their endangered status, little research has been conducted to characterize the relative sensitivity of sturgeons to DLCs. Proper assessment of risk of DLCs posed to these fishes therefore, requires a better understanding of this sensitivity and the factors that are driving it. Adverse effects associated with exposure to DLCs are mediated by the aryl hydrocarbon receptor (AhR). This study identified and characterized two distinct AhRs, AhR1 and AhR2, in white sturgeon (Acipenser transmontanus) for the first time as a first step in studying the relative sensitivities of sturgeons to DLCs. Furthermore, tissue-specific expression of both AhRs under basal conditions and in response to exposure to the model DLC, β-naphthoflavone (βNF), was determined. The sequence of amino acids of AhR1 of white sturgeon had greater similarity to AhRs of tetrapods, including amphibians, birds, and mammals, than to AhR1s of other fishes. The sequence of amino acids in the ligand binding domain of the AhR1 had greater than 80% similarity to AhRs known to bind DLCs and was less similar to AhRs not known to bind DLCs. AhR2 of white sturgeon had greatest similarity to AhR2 of other fishes. Profiles of expression of AhR1 and AhR2 in white sturgeon were distinct from those known in other fishes and appear more similar to profiles observed in birds. Expressions of both AhR1 and AhR2 of white sturgeon were greatest in liver and heart, which are target organs for DLCs. Furthermore, abundances of transcripts of AhR1 and AhR2 in all tissues from white sturgeon were greater than controls (up to 35-fold) following exposure to βNF. Based upon both AhRs having similar abundances of transcript in target organs of DLC toxicity, both AhRs being up-regulated following exposure to βNF, and both AhRs having greatest similarity to AhRs known to bind DLCs, it is hypothesized that both AhR1 and AhR2 of white sturgeon might mediate effects of DLCs in this species. Since current risk assessments are based on data derived largely from highly divergent fishes within the Salmonidae, presence of two functional AhRs in white sturgeon, one of which has greatest similarity to AhRs of birds, might have significant implications for the sensitivity of sturgeons to DLCs compared to other fishes.

Effects of Columbia River water on early life-stages of white sturgeon (Acipenser transmontanus)

The white sturgeon (Acipenser transmontanus) population that resides in the Columbia River in British Columbia (BC), Canada, has suffered recruitment failures for more than three decades. During the summers of 2008 and 2009, studies were performed to determine whether exposure to water downstream of a metal smelter in Trail, BC affected survival or growth of early life-stages of white sturgeon through 60+ days post-fertilization (dpf). In both years, there were no significant differences in survival of fish that were exposed to water from downstream compared to water from upstream of the smelter. At 20-21dpf, average mortality was 2.4 percent and 12 percent in upstream water for 2008 and 2009, respectively, which was similar to the average mortality of 3.8 percent and 7.2 percent in downstream water for 2008 and 2009, respectively. Relatively great mortality after 20-21dpf complicated analysis of the subchronic exposure, but use of a survival analysis indicated that the average fish died at 25-29dpf, regardless of whether the water to which they were exposed came from upstream or downstream of the smelter. In addition, measured concentrations of metals in river water were less than the threshold for adverse effects on early life stages of white sturgeon. Based upon these analyses, it is not likely that current concentrations of metals in the Columbia River in southern BC are adversely affecting survival of early life stages of white sturgeon larvae.