Toxicity and transformation of insecticide fenamiphos to the earthworm Eisenia fetida

This study was conducted to investigate the toxicity of the organophosphate insecticide fenamiphos to earthworms (Eisenia fetida) under laboratory conditions. Earthworms were exposed to soils differing in their physico-chemical properties spiked with fenamiphos at concentrations ranging from 10 to 200 mg kg(-1) for a period of 4 weeks. Residues of fenamiphos and its metabolites were determined in both soils and earthworms after 4 weeks of pesticide exposure. Fenamiphos was degraded faster in the alkaline soil than in the neutral and acidic soils. Median lethal concentration of fenamiphos in the neutral soil was 228 mg kg(-1) soil. Residues of fenamiphos caused a significant reduction in the biomass of worms, especially the ones exposed to the pesticide in the acidic soil. In vitro experiments suggested that fenamiphos was biotransformed in the earthworms principally to its oxide metabolite. To our knowledge, this is the first study demonstrating the biotransformation of fenamiphos by E. fetida.