Site-specific approach for setting water quality criteria for selenium : differences between lotic and lentic systems Adams, William J.; Toll, John E.; Brix, K. V.; Tear, Lucinda Marie; DeForest, D. K.
Results of an in-depth review of the literature indicates there are significant differences in the bioaccumulation of selenium by fishes and invertebrates from lotie (flowing) and lentic (standing) water bodies and that selenate is much less bioaccumulative than selenite. Bioaccumulation in fish is a factor of 10 or more higher in lentic systems as compared to lotic systems. These differences are a function of selenium's site-specific biogeochemical cycling. Further, we observed considerable variation in bird accumulation of selenium from site to site. To account for differences in bioaccumulation potential of selenium we developed a residue-based Bayesian Monte Carlo model to derive site-specific selenium water quality criteria protective offish and sensitive avian species. The approach uses data from a given site of interest to calibrate a model based on data from several other similar sites. When evaluating a specific site, the range of water and tissue concentrations is typically limited. This makes it difficult to use site-specific data to identify a water concentration sufficiently low that tissue concentrations do not exceed the tissue-effect threshold. Data from several similar sites provide a broader range of water and tissue residue concentrations that allow for an appropriate statistical extrapolation of the data to the site of interest. The Bayesian Monte Carlo model accounts for the significant site-to-site variability that exists in the relationship between water selenium and the mean tissue residue. In practice, data from similar sites are pooled to define a set of possible water and mean tissue residue relationships. This set of possible: relationships is then used with data from the site of interest to determine which relationships, from the set of possibilities, best fit the specific site. Once we have determined which set of possible relationship's fit the specific site, we extrapolate from the observed water concentration to a water concentration that results in a tissue residue concentration less than or equal to a chronic effect threshold. This value becomes the chronic water quality criterion.
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