Fate of 14C-chlorpyrifos in stored soybeans and its toxicological potential to mice

Grains of soybeans were treated with [ethyl-1-4C]chlorpyrifos at a dose of 15 ppm and its triplet. During the 30-week storage period, the penetration and distribution of insecticide residues were studied. The amount of surface residues on stored soybeans, internal extractables and bound residues were determined. Surface residues were found to decrease with the increase in time of storage, whereas internal residues showed a gradual increase with time to reach 40-52% of applied dose after 30 weeks. Non-extractable residues showed a relatively slow but definite increase with time. The degradation products include, in addition to the parent insecticide which constitutes 50% of the total residues, the oxygen-analogue of chlorpyrifos, desethyl chlorpyrifos and 3,5,6-trichloropyridinol. Feeding mice for 90 days with a diet mixed with total internal chlorpyrifos residues in stored soybeans led to considerably inhibited plasma and red blood cells-cholinesterase activity by 78 and 46%, respectively, during the experimental period. Blood picture, liver and kidney function of treated mice were significantly affected during the feeding period.