Bioconcentration of chlorpyrifos by the freshwater isopod Asellus aquaticus (L.) in outdoor experimental ditches

Abstract

The bioconcentration of the insecticide chlorpyrifos (CPF) [O,O-diethyl- O-(3,5,6-trichloro-2-pyridil) phosphorothioate] by the freshwater isopod Asellus aquaticus (L.) was investigated under time-varying exposure conditions in artificial outdoor ditches. The insecticide was applied as a single dose of Dursban 4E™ at nominal initial concentrations of the active ingredient of 0·7 and 5·0 μg litre −1. Toxicokinetic rate constants of CPF were estimated using three methods based on first-order onecompartment modelling. Aqueous concentrations of CPF showed a rapid exponential decrease. Tissue residues of CPF in Asellus, reached maximum values after two days with subsequent relatively rapid elimination in agreement with model predictions. Both uptake and elimination rate constants were dependent upon exposure level, with relatively low uptake and elimination rate constants (10 respectively 5-fold lower) at the high exposure level, which was attributed to toxic stress The time-dependent bioconcentration factor (BCF) of CPF did not show any dependence upon the exposure level, and reached a plateau after 2 days. Lipid-based BCF (1 kg −1; mean ± SE) values measured in the low and high treatments were 262 ± 77 × 10 3 ( n = 7) and 235 ± 44 × 10 3 ( n = 6), respectively, and were above ranges previously reported in the literature for fish. The feasibility of using freshwater isopods in biomonitoring programmes to assess the fate and effects of organophosphorus compounds is discussed.