Enantioselective bioaccumulation and toxic effects of metalaxyl in earthworm Eisenia foetida

Knowledge about the enantioselective bioavailability of chiral pesticides in soil invertebrates facilitates more accurate interpretation of their environmental behaviors. In this study, the acute toxicities of R-metalaxyl and rac-metalaxyl to earthworm (Eisenia foetida) were assayed by filter paper contact test. After 48 h of exposure, the calculated LC50 values for R- and rac-metalaxyl were 0.052 and 0.022 mg cm−2, respectively, resulting in a two fold difference in toxicity. For uptake experiment, earthworms were exposed in soil at two dose levels (10 and 50 mg kgdwt-1). The concentrations of two enantiomers in soil and earthworm were determined by high-performance liquid chromatography based on cellulose tri-(3,5-dimethylphenyl-carbamate) chiral stationary phase. The results showed that metalaxyl was taken up by earthworm rapidly, and the bioaccumulation of metalaxyl in earthworm was enantioselective with preferential accumulation of S-enantiomer. In addition, biota to soil accumulation factor (BSAF) used to express the bioaccumulation of metalaxyl enantiomers was investigated, and significant difference was observed between rac-metalaxyl and R-metalaxyl.

Research highlights
► R-metalaxyl was less toxic than racemate to earthworm.
► The chiral HPLC analysis method for metalaxyl in earthworm tissue was established.
► Metalaxyl was taken up by earthworm rapidly and enantioselectively.