No abstract

A model was recently published that relates the toxicity of copper to the most sensitive taxa in the U.S. Environmental Protection Agency's criteria database (Mytilus sp.) with dissolved organic carbon concentrations in saltwater. This model was developed for potential use in risk assessment and in the development of site-specific criteria (SSC) for copper in saltwater environments where Mytilus sp. is considered an appropriate indicator species. This manuscript presents the results of a field validation study of that model. Effective concentration 50% (EC(50)) values (n = 21) for seven sites were all predicted by the model within the previously established range of acceptability. Slopes and intercepts of the two data sets were not significantly different. Consequently, the data were pooled, and new equations were developed. Dissolved copper EC(50) values were highly correlated (r(2) = 0.76, n = 75, P < 0.0001) across a wide range of sample dissolved organic carbon (DOC) concentrations (0.3-12 mg C/L) and were explained by the equation EC(50) = 11.22 DOC(0.60). Two updated equations are proposed for consideration as a means of estimating site-specific final chronic criteria (FCC) and final acute criteria (FAC) for copper in marine and estuarine environments (copper FCC(DOC) = 3.59 DOC(0.60); copper FAC(DOC) = 5.61 DOC(0.60)).

Saltwater bivalves of the genus Mytilus are among the most copper sensitive taxa listed in both the current and recently proposed U.S. EPA ambient saltwater copper criteria documents. The copper saltwater quality criteria are somewhat unique in that the criteria were set specifically to protect Mytilus. However, there is considerable uncertainty in the reported taxonomy of Mytilus species in the criteria database and it has recently been demonstrated the copper toxicity to M. galloprovincialis is dependent on the organic matter content of the test water. A review of the toxicity and biogeography literature was conducted to rationalize the existing criteria database. Elimination of some data is suggested due to the uncertainty of test organism genotype. Moreover, due to the lack of reported dissolved organic matter content of the test waters in tests included in the criteria database, it is impossible to determine if the difference in species mean acute values reported in the criteria documents for Mytilus was due to differences in water chemistry or differences in species sensitivity. Experiments were designed and conducted with M. galloprovincialis and M. edulis (genetically confirmed) to determine if copper toxicity is a function of organic matter content for these two species and if there is a significant difference in species copper sensitivity. Results showed that copper toxicity is a function of organic matter concentration for both species and copper sensitivity of each species was statistically similar. Results support the normalization of the saltwater copper criteria database with respect to dissolved organic matter when developing ambient saltwater copper criteria. The USEPA toxicity database would benefit from future testing of M. trossulus and M. californianus.

The copper sensitivity of four saltwater invertebrates (the mussel Mytilus galloprovincialis, the oyster Crassostrea virginica, the sand dollar Dendraster excentricus, and the sea urchin Strongylocentrotus purpuratus) was determined experimentally using chronic-estimator embryo-larval test procedures. The effect of sample dissolved organic matter (DOM) content on Cu bioavailability was determined for these species using commonly prescribed test procedures. Comparisons were made among these test results and test results reported previously for two other invertebrate species: the mussel Mytilus edulis and the copepod Eurytemora affinis. All six species exhibited a direct and significant relationship between the sample dissolved organic carbon (DOC; a surrogate measure of DOM) and either the dissolved Cu median lethal concentration (LC50) values or median effect concentration (EC50) values. This relationship is significant even when the DOM has different quality as evidenced by molecular fluorescence spectroscopy. Once normalized for the effects of DOM, the Cu sensitivity of these species from least to most sensitive were E. affinis < D. excitricus < C. virginica approximately S. purpuratus approximately M. edulis approximately M. galloprovincialis. This ranking of species sensitivity differs from the saltwater species sensitivity distribution proposed in 2003 by the U.S. Environmental Protection Agency. These results support the need to account for factors that modify Cu bioavailability in future saltwater Cu criteria development efforts. More specifically, Cu saltwater species sensitivity distribution data will need to be normalized by factors affecting Cu bioavailability to assure that accurate and protective criteria are subsequently developed for saltwater species and their uses.

Synthetic sea salts are often used to adjust the salinity of effluent, ambient, and laboratory water samples to perform toxicity tests with marine and estuarine species. The U.S. Environmental Protection Agency (U.S. EPA) provides guidance on salinity adjustment in its saltwater test guidelines. The U.S. EPA suggests using commercial sea salt brands, such as Forty Fathoms (now named Crystal Sea Marinemix, Bioassay Grade), HW Marinemix, or equivalent salts to adjust sample salinity. Toxicity testing laboratories in Canada and the United States were surveyed to determine synthetic sea salt brand preference. The laboratories (n = 27) reported using four brands: Crystal Sea Marinemix (56%), HW Marinemix (22%), Instant Ocean (11%), and Tropic Marin (11%). Saline solutions (30 g/L) of seven synthetic sea salts were analyzed for dissolved copper and dissolved organic carbon (DOC) content. Brands included those listed above plus modified general-purpose salt (modified GP2), Kent Marine, and Red Sea Salt. The synthetic sea salts added from < 0.1 to 1.2 microg Cu/L to the solution. Solutions of Crystal Sea Marinemix had significantly elevated concentrations of DOC (range = 5.4-6.4 mg C/L, analysis of variance, Tukey, alpha = 0.05, p < 0.001) while other brands generally contained < 1.0 mg C/L. The elevated DOC in Crystal Sea Marinemix was expected to reduce copper toxicity. However, the measured dissolved copper effective concentration 50% (EC50) for Crystal Sea Marinemix was 9.7 microg Cu/L, similar to other tested sea salts. Analysis indicates that the organic matter in Crystal Sea Marinemix differs considerably from that of natural organic matter. On the basis of consistently adding little DOC and little dissolved copper, GP2 and Kent Marine are the best salts to use.

The basis for all US Environmental Protection Agency (USEPA) acute ambient water quality criteria is the chemical specific final acute value (FAV; an estimate of the concentration of the chemical corresponding to a cumulative probability of 0.05 of acute toxicity values for all genera with which acceptable acute tests have been conducted). The acute criterion for all chemicals is equal to the chemical's FAV divided by an application factor of 2. The intention of dividing the FAV by a factor of 2 is to convert the acute toxicity value to an incipient acute toxicity value, resulting in an acute criterion concentration that will protect against toxic effects to aquatic organisms. In the case of copper (Cu) in saltwater, the FAV is reduced from the normal 0.05 probability to equal to the genus mean acute value (GMAV; the geometric mean of copper effect concentration 50% [EC50] values) of the economically important marine bivalves of the genus Mytilus. Analyses to determine an application factor specific to Mytilus and copper were performed to assess the adequacy of the application factor of 2. An estimate of a dissolved copper application factor that is specific to and protective of Mytilus was determined using the results of sixty-four 48-h embryo survival and shell development copper toxicity tests of natural water samples collected from sites around the United States. A variety of point-estimate effects concentrations (EC1, EC5, EC10, EC20, and chronic values [ChV]) and statistical toxic-effect endpoints (no observed effect concentration [NOEC] and lowest observed effect concentration [LOEC]) were derived from the test results and compared. The most similar toxic effect endpoint estimates were EC1 approximately equal to NOEC, EC10 approximately equal to ChV, and EC20 approximately equal to LOEC. Probabilistic methods were used to determine a specific application factor with a high probability of providing protection. This analysis suggests that an application factor of 1.5 (rather than 2) is adequate to provide a high degree of protection against acute effects of dissolved copper to Mytilus. In context, this translates to an acute saltwater dissolved copper criterion of 6.4 microg Cu/L compared to the current acute criterion of 4.8 microg Cu/L.

The basis for all US Environmental Protection Agency (USEPA) acute ambient water quality criteria is the chemical specific final acute value (FAV; an estimate of the concentration of the chemical corresponding to a cumulative probability of 0.05 of acute toxicity values for all genera with which acceptable acute tests have been conducted). The acute criterion for all chemicals is equal to the chemical's FAV divided by an application factor of 2. The intention of dividing the FAV by a factor of 2 is to convert the acute toxicity value to an incipient acute toxicity value, resulting in an acute criterion concentration that will protect against toxic effects to aquatic organisms. In the case of copper (Cu) in saltwater, the FAV is reduced from the normal 0.05 probability to equal to the genus mean acute value (GMAV; the geometric mean of copper effect concentration 50% [EC50] values) of the economically important marine bivalves of the genus Mytilus. Analyses to determine an application factor specific to Mytilus and copper were performed to assess the adequacy of the application factor of 2. An estimate of a dissolved copper application factor that is specific to and protective of Mytilus was determined using the results of sixty-four 48-h embryo survival and shell development copper toxicity tests of natural water samples collected from sites around the United States. A variety of point-estimate effects concentrations (EC1, EC5, EC10, EC20, and chronic values [ChV]) and statistical toxic-effect endpoints (no observed effect concentration [NOEC] and lowest observed effect concentration [LOEC]) were derived from the test results and compared. The most similar toxic effect endpoint estimates were EC1 approximately equal to NOEC, EC10 approximately equal to ChV, and EC20 approximately equal to LOEC. Probabilistic methods were used to determine a specific application factor with a high probability of providing protection. This analysis suggests that an application factor of 1.5 (rather than 2) is adequate to provide a high degree of protection against acute effects of dissolved copper to Mytilus. In context, this translates to an acute saltwater dissolved copper criterion of 6.4 microg Cu/L compared to the current acute criterion of 4.8 microg Cu/L.