Physiological sensitivity of freshwater macroinvertebrates to heavy metals.

Macroinvertebrate species traits, such as physiological sensitivity, have successfully been introduced in trait-based bioassessment approaches and are important predictors of species sensitivity in the field. The authors ranked macroinvertebrate species according to their physiological sensitivity to heavy metals using toxicity data from acute laboratory assays. Rankings for each of the heavy metals, Cd, Cu, Cr, Ni, Pb, Zn, and Hg, were standardized based on all available species data. Rankings for different heavy metals on the species level showed no significant difference between compounds and were reasonably well correlated pairwise (0.50<r<0.73). Thus, an aggregated heavy metal ranking was developed, which assigns a single physiological sensitivity value (S(metal) ) to macroinvertebrate taxa. Considering the high variation, especially for higher taxonomic levels, that is, in the order level, it is recommended to use S values of the genus or species level for meaningful analyses. In terms of taxonomic ranking, crustaceans were overall the most sensitive taxonomic group, whereas insects were generally the most tolerant group. Species in the order of Cladocera were three orders of magnitude more sensitive than insects of the order of Trichoptera. By contrast, mollusks covered a wide range of sensitivities, with bivalves being on average one order of magnitude more sensitive than gastropods. The authors concluded that physiological sensitivity represents a promising trait for trait-based risk assessment that together with other demographic and recolonization traits may help to identify the effects of heavy metal pollution in aquatic ecosystems.