A combined toxicokinetics and toxicodynamics approach to investigate delayed lead toxicity in the soil invertebrate Enchytraeus crypticus

In a previous study, Pb toxicity was found to be delayed compared to Pb bioaccumulation in Enchytraeus crypticus. This study aimed at further investigating the acute and delayed onset of Pb toxicity in E. crypticus by using a combination of toxicokinetics and toxicodynamics approaches. Enchytraeids were exposed to different Pb concentrations (uptake phase) in natural LUFA 2.2 soil for different short-term exposure periods, followed by a 7-d elimination phase in clean soils. Body Pb concentrations and enchytraeid mortality were determined at different time intervals during both the exposure and the elimination phase. Pb uptake kinetics in E. crypticus were well described by a three-stage first-order model with an initial overshoot in body Pb concentrations. At higher exposure concentrations, Pb caused delayed enchytraeid mortality even following short-term exposure. LC50 based on body Pb concentrations appeared no good descriptor of delayed Pb toxicity in E. crypticus. Exposure time had a major impact on Pb bioaccumulation, toxicity and its delayed effects, which argues against relying on ecotoxicity tests for metal toxicity using a fix exposure duration. The presence of delayed toxic effects also suggests that post-exposure observations are necessary to avoid underestimation of metal toxicity.