Assessing acute and chronic copper risks to freshwater aquatic life using species sensitivity distributions for different taxonomic groups

Using copper as an example, we present a method for assessing chemical risk s to an aquatic community using species sensitivity distributions (SSDs) fo r different taxonomic groups. This method fits probability models to chemic al exposure and effects data to estimate the percentage of aquatic species potentially at risk and expands on existing probabilistic risk assessment m ethodologies. Due to a paucity of chronic toxicity data for many chemicals, this methodology typically uses an acute-chronic ratio (ACR) to estimate t he chronic effects distribution from the acute effects distribution. We exp anded on existing methods in two ways. First, copper SSDs were developed fo r different organism groups (e.g., insects, fish) that share similar sensit ivities or ecological functions. Integration of exposure and effects distri butions provides an estimate of which organism groups may be at risk. These results were then compared with a site-specific food web, allowing an esti mation of whether key food web components are potentially at risk and wheth er the overall aquatic community may be at risk from the perspective of eco system function. Second, chronic SSDs were estimated using the relationship between copper ACRs and acute toxicity (i.e., the less acutely sensitive a species, the larger the ACR). This correction in the ACR removes concerns previously identified with use of the ACR and allows evaluation of a signif icantly expanded chronic data set with the same approach as that for assess ing acute risks.