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There is concern over whether regulatory criteria for copper (Cu) are protective against chemosensory and behavioral impairment in aquatic organisms. We compiled Cu toxicity data for these and other sublethal endpoints in 35 tests with saltwater organisms and compared the Cu toxicity thresholds with biotic ligand model (BLM)-based estimated chronic limits (ECL values, which are 20% effect concentrations [EC20s] for the embryo-larval life stage of the blue mussel [Mytilus edulis], a saltwater species sensitive to Cu that has historically been used to derive saltwater Cu criteria). Only 8 of the 35 tests had sufficient toxicity and chemistry data to support unequivocal conclusions (i.e., a Cu EC20 or no-observed-effect concentration could be derived, and Cu and dissolved organic carbon [DOC] concentrations were measured [or DOC concentrations could be inferred from the test-water source]). The BLM-based ECL values would have been protective (i.e., the ECL was lower than the toxicity threshold) in 7 of those 8 tests. In the remaining 27 tests, this meta-analysis was limited by several factors, including 1) the Cu toxicity threshold was a "less than" value in 19 tests because only a lowest-observed-effect concentration could be calculated and 2) Cu and/or DOC concentrations often were not measured. In 2 of those 27 tests, the ECL would not have been protective if based only on a conservatively high upper-bound DOC estimate. To facilitate future evaluations of the protectiveness of aquatic life criteria for metals, we urge researchers to measure and report exposure-water chemistry and test-metal concentrations that bracket regulatory criteria. Environ Toxicol Chem 2018;37:1515-1522. © 2018 SETAC.

Acceptance of the biotic ligand model (BLM) to derive aquatic life criteria, for metals in general and copper (Cu) in particular, is growing among regulatory agencies worldwide. Thus, it is important to ensure that water quality data are used appropriately and consistently in deriving such criteria. Here we present a suggested BLM implementation framework (hereafter referred to as "the Framework") to help guide the decision-making process when designing sampling and analysis programs for use of the BLM to derive water quality criteria applied on a site-specific basis. Such a framework will help inform stakeholders on the requirements needed to derive BLM-based criteria, and thus ensure that the appropriate types and amount of data are being collected and interpreted. The Framework was developed for calculating BLM-based criteria when data are available from multiple sampling locations on a stream. The Framework aspires to promote consistency when applying the BLM across data sets of disparate water quality, data quantity, and spatial and temporal representativeness and is meant to be flexible to maximize applicability over a wide range of scenarios. Therefore, the Framework allows for a certain level of interpretation and adjustment to address the issues unique to each data set. Integr Environ Assess Manag 2018;14:736-749. © 2018 SETAC.

Copper (Cu) can impair olfaction in juvenile Pacific salmon (as well as other fishes), thus potentially inhibiting the ability of juveniles to avoid predators or to find food. Because Cu is commonly elevated in stormwater runoff in urban environments, storm events may result in elevated Cu concentrations in salmon-bearing streams. Accordingly, there is concern that existing Cu criteria, which were not derived using data for olfactory-related endpoints, may not be adequately protective of juvenile salmon. However, a modification of the US Environmental Protection Agency (USEPA) biotic ligand model (BLM) for deriving site-specific Cu criteria was recently proposed, which accounted for the sensitivity of olfactory endpoints. The modification was based on olfactory inhibition in juvenile coho salmon (Oncorhynchus kisutch) exposed to Cu in various combinations of pH, hardness, alkalinity, and dissolved organic carbon (DOC) concentrations. We used that olfactory-based BLM to derive 20% inhibition concentrations (IC20) values for Cu for 133 stream locations in the western United States. The olfactory BLM-based IC20 values were compared to the existing hardness-based Cu criteria and the USEPA's BLM-based Cu criteria for these representative natural waters of the western United States. Of the 133 sampling locations, mean hardness-dependent acute and chronic Cu criteria were below the mean olfactory-based BLM IC20 value in 122 (92%) and 129 (97%) of the waters, respectively (i.e.

The goal of this study was to evaluate the reliability of the Biotic Ligand Model to predict Cu toxicity in very hard surface water (>200 mg/L as CaCO3), relative to current copper criteria methodologies (hardness-based equation and the water-effect ratio; WER). To test these methods, we conducted acute Cu toxicity tests with three aquatic test species (Ceriodaphnia dubia, Daphnia pulex and Pimephales promelas) in seven surface waters. The sites were representative of effluent-dependent or effluent-dominated streams common to the arid western United States of America (arid West) and a wide range of water quality variables were tested. In addition, concurrent Cu toxicity tests were conducted in laboratory waters that were matched to hardness and alkalinity of the sites to facilitate calculation of WER values. Results were used to characterize empirical relationships between water quality characteristics and Cu toxicity, and to compare measured Cu toxicity with Biotic Ligand Model (BLM) predictions. Acute toxicity tests were also conducted with C. dubia and P. promelas in a range of Ca or Mg-dominated hardness concentrations to determine the independent effects of Ca or Mg on Cu toxicity at high hardness levels. Conclusions from this study suggest that the BLM generates appropriate criteria for the waters tested in this study when compared to the hardness-based equation or WER approach. Although the historical site-specific methods are useful for surface waters with hardness ≤250 mg/L as CaCO3, the unique conditions of arid West streams require site-specific methods that account for the influences of critical water quality variables (i.e., pH, dissolved organic carbon, alkalinity, Ca, Mg and Na). Therefore, the BLM offers an improved alternative to the hardness-based and WER approaches, particularly for situations where the current methods would be under-protective of sensitive aquatic life.

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).

Water pH in the gill micro-environment of adult fathead minnows (Pimephales promelas Rafinesque) was measured by means of opercular catheters and latex masks. Synthetic soft water of pH 5.7 was made more acidic, so that pH of the gill micro-environment stayed at approximately 5.4 to 5.9 over the inspired pH range 4.8 to 6.3. Copper would therefore be >99% Cu2+ at the gills. To measure Cu accumulation on gills, the target organ for Cu toxicity, adult fathead minnows were exposed for 2 to 3 h to 16 μg/L Cu in synthetic soft water (Ca2+ and Na+ approximately 50 μeq/L) at pH 4.8 and 6.3. Gill Cu concentrations were about 1.7 μg Cu/g wet tissue for the inspired pH 4.8 and 6.3 exposures. Added Ca2+ of 2,100 or 4,000 μeq/L reduced gill Cu accumulation during exposures at pH 4.8 but not at pH 6.3. EDTA eliminated Cu deposition at both pH 4.8 and pH 6.3 when equimolar with Cu, but reduced Cu deposition (by 50%) when half equimolar only in the pH 4.8 exposures. These results can be explained by Ca2+ and H+ competition with Cu for gill binding sites and by complexation of Cu by EDTA. Added CaCO3 did not reduce gill Cu, although both competition by Ca2+ and complexation by CO2−3 were expected. Water chemistry calculations suggested that because little CO2−3 is available at pH < 7, CO2−3 from CaCO3 is less likely to affect Cu deposition on fish gills than is Ca2+ from CaCO3.

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 mitigating effect of increasing hardness on metal toxicity is reflected in water quality criteria in the United States over the range of 25–400 mg l −1 (as CaCO 3 ). However, waters in the arid west of the US frequently exceed 400 mg l −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 1200 mg l −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 ±2 X of observed EC 50 values, and thus may be more useful than hardness for modifying water quality criteria.