Toxicokinetic variation in 15 freshwater arthropod species exposed to the insecticide chlorpyrifos

Recent advances in modeling the processes of the toxicity of chemicals—toxicokinetics (TK) and toxicodynamics (TD)—are improving environmental risk assessment (ERA) through prediction of effects from time-varying exposure. This has been achieved by linking chemical fate and toxicological effects mechanistically, based on internal concentrations, through the tissue residue approach. However, certain questions remain: for example, how do TK and TD differ among species and how does this relate to differences in species sensitivity? In a series of experiments, we studied the TK of [14C]chlorpyrifos in 15 freshwater arthropod species, two of which were studied in juvenile and adult life stages. Uptake (kin) and elimination (kout) rate constants were fitted using a one-compartment single first-order kinetic model. The application of two complementary parameter estimation methods facilitated the calculation of bioconcentration factors (BCF) with prediction intervals and 95% depuration times (t95) for all tested species. Extremely slow elimination was observed in some species as well as high overall variation in kin, kout, BCF, and t95 across the tested aquatic arthropod species. This variation has implications for the development of TKTD approaches in ERA, including assessing fluctuating exposure concentrations and the interpretation of observed toxicity responses in the laboratory and in the field.