Pesticide Body Burden of the Crustacean Gammarus pulex as a Measure of Toxic Pressure in Agricultural Streams.

Risk assessments of toxicants in aquatic environments are typically based on the evaluation of concentrations in water or sediment. However, concentrations in water are highly variable, while the body burden may provide a better time-integrated measure of pesticide exposure and potential effects in aquatic organisms. Here, we quantified pesticide body burdens in a dominant invertebrate species from agricultural streams, Gammarus pulex, compared them with pesticide concentrations in water samples, and linked the pesticide contamination with observed ecological effects on macroinvertebrate communities. In total, 19 of 61 targeted analytes were found in the organisms, ranging from 0.037 to 93.94 ng g (wet weight). Neonicotinoids caused the highest toxic pressure among the pesticides detected in G. pulex. Using linear solvation energy relationships (LSERs), we derived equivalent pesticide concentrations in streamwater based on the body burden. These equivalent concentrations correlated with the concentrations in water samples collected after runoff (65% of variance explained). Pesticide pressure significantly affected the aquatic macroinvertebrate community structure, expressed as SPEAR, and caused, on average, 3-fold increased insecticide tolerance in G. pulex as a result of adaptation. The toxic pressure derived from body burden and from water samples similarly explained the change in community structure (68% and 64%). However, the increased tolerance of G. pulex to pesticides was better explained by the toxicity derived from body burden (70%) than by the toxicity from water samples (53%). We conclude that the internal body burden of macroinvertebrates is suitable to assess the overall pesticide exposure and effects in agricultural streams.