Dissipation of cypermethrin and its major metabolites in litter and elm forest soil

Cypermethrin (40 EC Ripcord(R), 1.0 g a.i./L aqueous dilution) was applied to the basal 1 m of elm tree trunks to runoff for control of elm bark beetles at two different application times and sites. The initial residues of cis-A, trans-C, cis-B, and trans-D cypermethrin isomers in litter were 54 to 141, 41 to 125, 47 to 88, and 32 to 62 mu g/g, respectively, depending on the application time, and dissipated to below detection limits at 341 d after application. Total cypermethrin residues in soil fluctuated from below detection limits to 10 mu g/g during the experimental period. Dissipation half-lives of cis-A, trans-C, cis-B, and trans-D in soil fortified in the laboratory and held under field conditions were 409 to 453, 277 to 286, 345 to 473, and 249 to 263 d, respectively. The trans-cypermethrin isomers dissipated more quickly in soil than the cis-isomers, and cypermethrin at higher concentrations dissipated more slowly than at lower concentrations.