LAUSR

Chlorpyrifos (CPF), a broad-spectrum neurotoxic organophosphate insecticide, is subject to atmospheric and hydrolytic transport from application sites to aquatic ecosystems. Across the landscape, concentrations in surface water can vary spatially and temporally according to seasonal use practices. Standardized bioassays can provide a screening-level understanding of aquatic receptor acute and chronic toxicity. However, these bioassays do not address ecologically relevant exposure patterns that may impact fitness and survival within and across generations. The aim of this research was to evaluate the utility of a second-tier, screening-level methodology employing Daphnia magna multi- and trans-generational bioassays spanning 4 generations to investigate the effect of variable chronic CPF exposure. The multi-generational assay consisted of continuous CPF exposure across 4 consecutive 21d bioassays using progeny from the previous assay for each successive generation. In the trans-generational assay, only the parent (F0) generation was exposed. For both assays, survival and reproduction were assessed across treatments and generations. Results indicated that 1) following continuous CPF exposure at ecologically relevant concentrations to 4 generations of D. magna, the highest treatment showed an apparent tolerance response for both survival and reproductive success in the F3 generation, and 2) CPF exposure to the F0 generation did not result in treatment effects in the unexposed F1, F2, and F3 generations in the apical endpoints of survival and reproduction. Employing a suite of acute and chronic bioassays, including chronic exposures spanning multiple generations, allows for a more robust screening-level evaluation of the potential impact of CPF on aquatic receptors for variable periods of exposure. This article is protected by copyright. All rights reserved.