Fate of aged tolclofos-methyl and diethofencarb residues in soil

Abstract

The fate of bound residues originating from ¹⁴C-labeled tolclofos-methyl and diethofencarb was examined in the presence and absence of organic amendments. After 3-month incubation with ¹⁴C-labeled pesticides at 20±2°C under dark conditions, the equivalent weight of fresh soil or organic matter (0.3% dry weight basis) was added to the soil and further incubated for six months to investigate the effect of additions on the bound residues. Only 4–11% of aged ¹⁴C-residues was extracted with aqueous organic solvents, indicating that most of them tightly bound to soil. Addition of fresh soil or organic matter caused slightly higher mineralization than in control soil, resulting in the 11–24% release of bound ¹⁴C six months after additions. Although bound residues in aged soil were found not to be easily released even by organic solvents, they could be utilized by microbes and gradually mineralized.