Assessing the Relative Sensitivity of Aquatic Organisms to Divalent Metals and Their Representation in Toxicity Datasets Compared to Natural Aquatic Communities

We compared the composition and richness of acute and chronic toxicity datasets for Cd, Cu, Ni, Pb, and Zn to several natural aquatic communities. The richness of acute datasets was reasonably representative, with the largest toxicity datasets containing a higher number of genera than some natural aquatic communities. Acute datasets also had a reasonably diverse composition compared to natural aquatic communities, although insects were under-represented and cladocerans over-represented. Given this robustness, we suggest manipulation of large acute datasets (Cd, Cu, Zn) to account for site-specific differences in aquatic community composition can be accomplished with confidence and that this will not result in under-protection of sensitive taxa. In contrast, the chronic datasets were not representative of natural aquatic communities in terms of composition or richness. Chronic dataset richness is an order of magnitude less than natural aquatic communities. Chronic datasets have minimal representation of insects, whereas cladocera and salmonids are grossly over-represented in some cases. Further, no real patterns in the relative sensitivity of genera groups can be discerned with such limited data. As a result, we conclude there is considerable uncertainty regarding how biases in genera representation may lead to under- or over-protection of aquatic communities on a chronic basis. Given this, manipulation of chronic datasets to better reflect site-specific aquatic communities is not recommended without additional chronic testing using a wider diversity of aquatic genera.