The Persistence of 2,4,5-T in a Pacific Northwest Forest'

The concentrations of 2,4,5-T ((2,4,5-trichloro- phenoxy)acetic acid) in four species of vegetation varied from 11 to 1 5 ppmw immediately after application at 2.24 kg/ha but were less than 0.5 ppmw after 1 yr. The 2,4,5-T level in forest floor declined 90% during the first 6 months after appli- cation and less than 0.02 kg/ha remained after 1 yr. There was little leaching of 2,4,5-T from the forest floor into soil and no residues were found deeper than 15 cm. Maximum soil resi- dues did not exceed 0.1 ppmw. Residue levels and dissipation rates of 2,4,5-T were similar after one and two successive annual applications.