Evaluating environmental hazards of land applying composted diazinon usingearthworm bioassays

Environmental hazards resulting from land application of composted pesticid e residue have not been rigorously evaluated. This study was conducted to e xamine the toxicity of a composted pesticide residue using earthworms (Eise nia foetida Savigny) as a microinvertebrate model in a soil bioassay system . Diazinon, which was used in these experiments as a test pesticide, was re moved from simulated rinsate (wastewater) by sorption onto peat moss. Follo wing the rinsate clean-up phase, diazinon-laden peat moss was placed into b ioreactors and composted for either 30 or 60 days. Earthworms were then exp osed to soil amended with the composted material. Mortality and symptomatic effects characteristic of acetylcholinesterase inhibition, including weigh t loss, reduced burying ability and curling, occurred in earthworms exposed to soil amended with either uncomposted or 30-day composted diazinon, but not in those exposed to soil amended with 60-day composted diazinon. The am ount of solvent-extractable diazinon from compost was not directly related to acute earthworm toxicity based on the selected criteria. These results i ndicated a reduction in diazinon bioavailability during latter 30 d of comp osting that did not correspond to a reduction in solvent-extractable diazin on concentrations. Measuring symptomatic effects of xenobiotics as describe d in this study may increase the sensitivity and diagnostic ability of eart hworm bioassays.