Dissipation of chlorpyrifos, oxon, and 3,5,6-trichloro-2-pyridinol in litter and elm forest soil

After chlorpyrifos was applied to the basal 1 meter of elm tree trunks for control of elm bark beetles at two different application times and sites, initial chlorpyrifos residues in forest floor litter ranged from 120 to 916 mu g/g depending on the application time. Residues dissipated by approximately 99% after 791 d with the DT50 from 3.9 to 59 d and DT90 from 55 to 310 d. The initial residues of chlorpyrifos in elm forest soil varied from 0.8 to 28 mu g/g and were 1 to 2 mu g/g at 791 d after application. The dissipation half-lives of chlorpyrifos in fortified soil placed in the field ranged from 116 to 121 d.