METABOLITES OF [C-14] 2,4-DICHLOROPHENOXYACETIC ACID IN SASKATCHEWAN SOILS

The transformation of 2.0-mu-g/g ring-labeled [C-14]-2,4-dichlorophenoxyacetic acid was investigated, in the dark under controlled laboratory conditions, in four soils at 85% field capacity and at 20-degrees-C. The rates of herbicide breakdown were reflected in the numbers of 2,4-D-degrading organisms isolated from the soils at the four sites. Over a 24-day period in soils with no recent herbicide history, more than 89% of the applied 2,4-D was metabolized with 25-31% of the applied C-14 being released as carbon dioxide, 2-10% being solvent recoverable as [C-14]-2,4-dichloroanisole, and 39-43% being associated with soil in a solvent-nonextractable form. In soils with prior 2,4-D treatments herbicide degradation was faster with approximately 50% of the applied radioactivity being released as carbon dioxide, 1-4% being solvent recoverable as [C-14]-2,4-dichlorophenol and 2-5% as [C-14]-2,4-dichloroanisole, and 22-30% of the initial C-14 associated with the soil in a solvent-nonextractable form.