Effects of in situ selenium exposure and maternal transfer on survival and deformities of brown trout (Salmo trutta) fry.

Offspring of wild adult brown trout exposed to a range of Se concentrations were reared in a laboratory setting to primarily assess effects on survival and deformities. Maternal whole-body Se concentrations ranged from 4.7 to 22.6 mg/kg dry weight for wild fish. Corresponding Se concentrations in embryos ranged from 6.2 to 40.3 mg/kg dry weight. Significant relationships were found between embryo and whole-body tissue concentrations. Increasing egg Se concentrations were correlated with decreasing survival; however, hatch success was not significantly correlated with increasing embryo Se. The best fit effect concentration, 10% (EC10) for survival in the hatch to swim-up period was 20.6 mg/kg dry weight, and the EC10 for hatch to test termination at 88 d was 20.5 mg/kg dry weight egg Se. The best fit model for deformities was based on a baseline-adjusted severity index and resulted in an EC10 of 21.8 mg/kg dry weight egg Se. Both the best fit model EC10s represent more sensitive values than the published range of trout species EC10s. An egg to whole-body tissue conversion factor derived from the paired data resulted in a conversion factor for brown trout of 1.46, which resulted in a whole-body tissue EC10 of 14.04 mg/kg dry weight at an egg tissue EC10 of 20.5 mg/kg dry weight. Environ Toxicol Chem 2018;37:1396-1408. © 2018 SETAC.

Influence of Varying Water Quality Parameters on the Acute Toxicity of Silver to the Freshwater Cladoceran, Ceriodaphnia dubia.

The acute toxicity of silver to Ceriodaphnia dubia was investigated in laboratory reconstituted waters as well as in natural waters and reconstituted waters with natural organic matter. The water quality characteristics of the laboratory reconstituted waters were systematically varied. The parameters that demonstrated an ability to mitigate the acute toxic effects of silver were chloride, sodium, organic carbon, and chromium reducible sulfide. Factors that did not have a consistent effect on the acute toxicity of silver to C. dubia, at least over the range of conditions tested, included hardness, alkalinity, and pH. The biotic ligand model was calibrated to the observed test results and found to be of use in quantifying the effect of changing water quality characteristics on silver bioavailability and toxicity. The model generally predicted silver toxicity within a factor of two and should be useful in modifying water quality criteria.

The interactive toxicity of cadmium, copper, and zinc to Ceriodaphnia dubia and rainbow trout (Oncorhynchus mykiss).

Traditionally, aquatic toxicity studies examine the toxicity of a single chemical to an organism. Organisms in nature, however, may be exposed to multiple toxicants. Given this is a more realistic exposure scenario in situ, the authors sought to understand the interactive toxicity of multiple metals to aquatic organisms. The authors performed a series of studies using equitoxic mixtures of cadmium, copper, and zinc to 2 aquatic organisms, rainbow trout (Oncorhynchus mykiss) and the waterflea, Ceriodaphnia dubia. Single metal toxicity tests were conducted to determine the acute median lethal concentration (LC50) values for O. mykiss and short-term, chronic median effective concentration (EC50) values for C. dubia. All 3 metals were then combined in equitoxic concentrations for subsequent mixture studies using a toxic unit (TU) approach (i.e., 1 TU = EC50 or LC50). For C. dubia, the mixture study showed greater-than-additive effects in hard water (TU-based EC50 = 0.74 TU), but less-than-additive effects in soft water (TU-based EC50 = 1.93 TU). The mixture effects for O. mykiss showed less-than-additive effects in both hard and soft waters, with TU-based LC50 values of 2.33 total TU and 2.22 total TU, respectively. These data are useful in helping understand metal mixture toxicity in aquatic systems and indicate that although in most situations the assumption of additivity of metal mixture toxicity is valid, under certain conditions it may not be sufficiently protective.

Identifying the cause of toxicity in an algal whole effluent toxicity study - an unanticipated toxicant.

Toxicity was observed in whole effluent toxicity (WET) studies with the freshwater alga, Pseudokirchneriella subcapitata, in three consecutive monthly studies, (NOEC=50-75%). Toxicity was not observed to Ceriodaphnia dubia or the fathead minnow, Pimephales promelas in concurrent studies. Selected toxicity identification evaluation (TIE) tests were conducted in a tiered approach to eliminate possible toxicants and progressively identify the causative agent. Filtration following alkaline adjustment (pH 10 or 11) was effective in eliminating significant growth effects and also reduced phosphate concentration. The TIE studies confirmed that the observed effluent toxicity was caused by excess ortho-phosphate in the effluent not by overstimulation or related to unfavorable N:P ratios; but due to direct toxicity. The 96-h 25% inhibition concentration (IC25) of ortho-phosphate to P. subcapitata was 3.4 mg L⁻¹ while the maximum acceptable toxicant concentration was 4.8 mg L⁻¹. This study illustrates the value of multi-species testing and also provides an example of an effective TIE using algae identifying an unanticipated toxicant.

The effect of food on the acute toxicity of silver nitrate to four freshwater test species and acute-to-chronic ratios.

Acute silver toxicity studies were conducted with and without food for four common freshwater test species: Daphnia magna, Ceriodaphnia dubia, Pimephales promelas (fathead minnow-FHM), and Oncorhynchus mykiss (rainbow trout-RBT) in order to generate acute-to-chronic ratios (ACR). The studies were conducted similarly (i.e., static-renewal or flow-through) to chronic/early-life stage studies that were previously performed in this laboratory. The acute toxicity (EC/LC50 values) of silver without food ranged from 0.57 µg dissolved Ag/l for C.dubia to 9.15 µg dissolved Ag/l for RBT. The presence of food resulted in an increase in EC/LC50 values from 1.25× for RBT to 22.4× for C. dubia. Invertebrate food type was also shown to effect acute silver toxicity. Food did not affect EC/LC50s or ACRs as greatly in fish studies as in invertebrate studies. ACRs for both invertebrate species were <1.0 when using acute studies without food but were 1.22 and 1.33 when using acute studies with food. ACRs for FHMs ranged from 4.06 to 7.19, while RBT ACRs ranged from 28.6 to 35.8 depending on whether food was present in acute studies. The data generated from this research program should be useful in re-determining a final ACR for silver in freshwater as well as in risk assessments.

Comparison of short-term chronic and chronic silver toxicity to fathead minnows in unamended and sodium chloride-amended waters.

The chronic (early life stage [ELS]) and short-term chronic (STC) toxicity of silver (as silver nitrate) to fathead minnows (FHM) was determined concurrently in flow-through exposures (33 volume additions/d). Paired ELS (approximately 30 d) and STC (7 d) studies were conducted with and without the addition of 60 mg/L Cl (as NaCl). The paired studies in unamended water were later repeated using standard flow conditions (9 volume additions/d). The purpose of the paired studies was to determine if short-term chronic endpoints can be used to predict effects in ELS studies. For each experiment, a "split-chamber" design (organisms were held in a common exposure chamber) allowed the direct comparison between short-term and chronic exposures. It appeared that the chronic toxicity of silver was mitigated to some extent by NaCl addition. The maximum acceptable toxicant concentration for growth in the ELS study was 0.53 microg dissolved Ag/L under standard flow conditions. Early life stage and STC endpoints in all three studies typically agreed within a factor of two. Whole-body sodium and silver concentrations measured in individual fathead minnows during these studies showed an increase in silver body burdens and a decrease in sodium concentration. These results indicate that the STC study could be used as a surrogate test to estimate chronic toxicity and that the mechanism of chronic silver toxicity may be the same as for acute toxicity.

Reprint of "Chronic toxicity of silver nitrate to Ceriodaphnia dubia and Daphnia magna, and potential mitigating factors".

We investigated the chronic toxicity of Ag, as silver nitrate, using two freshwater aquatic cladoceran species, Ceriodaphnia dubia and Daphnia magna, to generate data for the development of a chronic ambient water quality criterion for Ag. Preliminary studies with C. dubia showed variable results which were related to the equilibration time between food and silver. Follow-up testing was conducted using a 3 h equilibration time, which stabilized dissolved Ag concentrations and the toxicity of Ag(+). Results with C. dubia conducted individually (1 per cup, n=10) and in mass (30 per chamber, n=2) gave similar results once similar standardized equilibration times were used. The maximum acceptable toxicant concentration (MATC) of Ag to C. dubia and D. magna was 9.61 and 3.00 microg dissolved Ag/L, respectively. The chronic toxicity of Ag(+) to C. dubia was also evaluated in the presence of: (1) dissolved organic carbon (DOC) and (2) sulfide. The addition of DOC (0.4 mg/L) resulted in a approximately 50% decrease in toxicity while the addition of sulfide (75.4 nM) deceased toxicity by 42%. Whole-body Ag concentration in D. magna was positively correlated with increased levels of Ag exposure, however; we observed a non-statistical decrease in whole-body Na levels, an estimator of sodium homeostasis.

Effects of sodium chloride on chronic silver toxicity to early life stages of rainbow trout (Oncorhynchus mykiss).

The chronic (early life stage) toxicity of silver to rainbow trout (Oncorhynchus mykiss) was determined in flow-through exposures. Rainbow trout embryos were exposed to silver (as AgNO3) from 48 h or less postfertilization to 30 d postswimup in soft water in the presence and absence of 49 mg/L of NaCl (30 mg/L of Cl). The studies determined effect levels for rainbow trout exposed throughout an extended development period and assessed possible protective effects of sodium chloride. Lowest-observed-effect concentrations were greater than 1.25 microg/L of dissolved silver for survival, mean day to hatch, mean day to swimup, and whole-body sodium content in both studies. Whole-body silver concentrations increased significantly at 0.13 microg/L of dissolved silver in unmodified water and at 1.09 microg/L of dissolved silver in amended water. The maximum-acceptable toxicant concentration for growth was greater than 1.25 microg/L of dissolved silver in unmodified water and 0.32 microg/L of dissolved silver in amended water. Whole-body silver concentrations were more sensitive than survival and growth end points in unmodified water. Interpretation of sodium chloride effects on chronic silver toxicity to rainbow trout was complicated by differences in measured effect levels that were potentially the result of strain differences between test organisms in the two studies.

Chronic toxicity of silver nitrate to Ceriodaphnia dubia and Daphnia magna, and potential mitigating factors.

We investigated the chronic toxicity of Ag, as silver nitrate, using two freshwater aquatic cladoceran species, Ceriodaphnia dubia and Daphnia magna, to generate data for the development of a chronic ambient water quality criterion for Ag. Preliminary studies with C. dubia showed variable results which were related to the equilibration time between food and silver. Follow-up testing was conducted using a 3h equilibration time, which stabilized dissolved Ag concentrations and the toxicity of Ag(+). Results with C. dubia conducted individually (1 per cup, n=10) and in mass (30 per chamber, n=2) gave similar results once similar standardized equilibration times were used. The maximum acceptable toxicant concentration (MATC) of Ag to C. dubia and D. magna was 9.61 and 3.00microg dissolved Ag/L, respectively. The chronic toxicity of Ag(+) to C. dubia was also evaluated in the presence of: (1) dissolved organic carbon (DOC) and (2) sulfide. The addition of DOC (0.4mg/L) resulted in a approximately 50% decrease in toxicity while the addition of sulfide (75.4nM) deceased toxicity by 42%. Whole-body Ag concentration in D. magna was positively correlated with increased levels of Ag exposure, however; we observed a non-statistical decrease in whole-body Na levels, an estimator of sodium homeostasis.

Effect of culture water hardness on the sensitivity of Ceriodaphnia dubia to copper toxicity.

We examined whether the sensitivity of Ceriodaphnia dubia to copper toxicity was influenced by the hardness of the water in which they were reared or in which they were exposed. Organisms cultured in very hard water were 1.5-fold less sensitive to copper than those in moderately hard water. However, the hardness of the exposure water had a greater (2.5-fold) effect on copper median effective concentration (EC50s).

The biotic ligand model: a historical overview.

During recent years, the biotic ligand model (BLM) has been proposed as a tool to evaluate quantitatively the manner in which water chemistry affects the speciation and biological availability of metals in aquatic systems. This is an important consideration because it is the bioavailability and bioreactivity of metals that control their potential to cause adverse effects. The BLM approach has gained widespread interest amongst the scientific, regulated and regulatory communities because of its potential for use in developing water quality criteria (WQC) and in performing aquatic risk assessments for metals. Specifically, the BLM does this in a way that considers the important influences of site-specific water quality. This journal issue includes papers that describe recent advances with regard to the development of the BLM approach. Here, the current status of the BLM development effort is described in the context of the longer-term history of advances in the understanding of metal interactions in the environment upon which the BLM is based. Early developments in the aquatic chemistry of metals, the physiology of aquatic organisms and aquatic toxicology are reviewed first, and the degree to which each of these disciplines influenced the development of water quality regulations is discussed. The early scientific advances that took place in each of these fields were not well coordinated, making it difficult for regulatory authorities to take full advantage of the potential utility of what had been learned. However, this has now changed, with the BLM serving as a useful interface amongst these scientific disciplines, and within the regulatory arena as well. The more recent events that have led to the present situation are reviewed, and consideration is given to some of the future needs and developments related to the BLM that are envisioned. The research results that are described in the papers found in this journal issue represent a distinct milestone in the ongoing evolution of the BLM approach and, more generally, of approaches to performing ecological assessments for metals in aquatic systems. These papers also establish a benchmark to which future scientific and regulatory developments can be compared. Finally, they demonstrate the importance and usefulness of the concept of bioavailability and of evaluative tools such as the BLM.

Evaluating the role of ion composition on the toxicity of copper to Ceriodaphnia dubia in very hard waters.

The mitigating effect of increasing hardness on metal toxicity is reflected in water quality criteria in the United States over the range of 25-400 mgl(-1) (as CaCO(3)). However, waters in the arid west of the US frequently exceed 400 mgl(-1) hardness, and the applicability of hardness-toxicity relationships in these waters is unknown. Acute toxicity tests with Ceriodaphnia dubia were conducted at hardness levels ranging from approximately 300 to 1,200 mgl(-1) using reconstituted waters that mimic two natural waters with elevated hardness: (1) alkaline desert southwest streams (Las Vegas Wash, NV), and (2) low alkalinity waters from a CaSO(4)-treated mining effluent in Colorado. The moderately-alkaline EPA synthetic hard water was also included for comparison. Copper toxicity did not consistently vary as a function of hardness, but likely as a function of other water quality characteristics (e.g., alkalinity or other correlated factors). The hardness equations used in regulatory criteria, therefore, may not provide an accurate level of protection against copper toxicity in all types of very hard waters. However, the mechanistic Biotic ligand model generally predicted copper toxicity within +/-2X of observed EC(50) values, and thus may be more useful than hardness for modifying water quality criteria.

The effect of calcium and magnesium ratios on the toxicity of copper to five aquatic species in freshwater.

While it is generally accepted that water hardness affects copper toxicity, the major ions that contribute to water hardness (calcium [Ca] and magnesium [Mg]) may affect copper toxicity differently. This is important because the Ca:Mg ratio in standard laboratory-reconstituted waters often differs from the ratio in natural surface waters. Copper toxicity was assessed for five different aquatic species: rainbow trout (RBT), fathead minnow (FHM), Ceriodaphnia dubia, Daphnia magna, and an amphipod (Gammarus sp.) under different Ca:Mg ratios (4:0, 3:1, 1:1, 1:3, and 1:4 mass basis) at a common hardness (180 mg/L as CaCO3) and alkalinity (120 mg/L as CaCO3). Copper toxicity increased at lower Ca:Mg ratios for RBT but increased at higher Ca:Mg ratios for D. magna. Fathead minnows (<24 h old) were more sensitive to copper in 1:1 Ca:Mg waters compared to 3:1 Ca:Mg waters. The toxicity of copper did not vary under different Ca:Mg ratios for Gammarus sp., C. dubia, and 28-d-old FHM. The effect of Ca:Mg ratios on copper toxicity changed for D. magna in softer water (90 mg/L as CaCO3) compared with hard water studies.