Canadian Water Quality Guidelines for the Protection of Agricultural Water Uses - Diclofop-methyl

The fate and persistence of diclofop-methyl and diclofop in soil may be influenced by major processes such as chemical and biological degradation. In addition, losses in runoff occur because of its ability to adsorb strongly to soil particles. Up to 15% of diclofop-methyl is hydrolyzed at the time of application and incorporated into the soil, and as much as 85% is hydrolyzed within 24 h of application. Afterwards, the rate of diclofop-methyl hydrolysis declines (Smith 1977; Martens 1978). Under laboratory conditions, a half-life value for diclofop-methyl residues of <3 d was reported (Wink and Luley 1988). Degradation of the hydrolysis product, diclofop, occurs primarily by biological decomposition (Smith 1979b). The half-life of diclofop ranged from 6 to 38 d in soil under aerobic conditions. Under anaerobic conditions, the halflife was 150 d or longer (Martens 1978). With time, the rate of diclofop biodegradation levels off, and the residual concentrations are apparently bound to soil organic matter (Martens 1978; Smith 1979b).