Persistence, degradation and leaching of coumaphos in soil

Dissipation, degradation and leaching of fresh C-14 coumaphos, alkylated C- 14 coumaphos and aged residues of C-14 coumaphos from vats were studied in alkaline sandy loam soil in soil columns in the field under subtropical con ditions in Delhi for a year. Dissipation, degradation and bound residue for mation was more in case of alkali treated coumaphos than fresh coumaphos. A fter 365 days total residues of fresh coumaphos accounted for 33.25% while that of alkali treated coumaphos was 19.12%. Bound residue formation was al most double in case of alkali treated coumaphos (18.95%) than fresh coumaph os (9.53%) after 150 days followed by release of bound residue in both the cases. The proportion of metabolites 4 - methylumbelliferone, chlorferon an d potasan collectively was 86.05% in fresh coumaphos extractable residues w hile the same was 91.74% in alkali treated coumaphos after 365 days. Aged r esidues from vats containing copper sulphate and buffer were found to be mo re persistent in soil as total residues remained were 95.58% in comparison with 83.09% total residues of aged residues from vats containing only buffe r after 150 days of treatment. Copper sulphate seems to inhibit the degrada tiion of coumaphos in soil by microorganisms. Chlorferon was the major meta bolite in generally all the samples. Coumaphos did not leach below 10 cm in all the cases.