Degradation of [14C]terbuthylazine and [14C]atrazine in laboratory soil microcosms

The degradation and formation of major chlorinated metabolites of terbuthylazine and atrazine in three soils (loamy clay, calcareous clayand high clay) were studied in laboratory experiments using molecules labelled with{sup} 14{end}C on the s-triazine ring. Soil microcosmswere treated with the equivalent of 1 kg ha{sup} -1{end} of herbicide and incubated in the dark for 45 days at 20(q 1) deg.C. The quantity of [{sup} 14{end}C]carbon dioxide evolved in the soils treated withatrazine was negligible and could not be attributed to mineralization of the parent molecule. The mineralization of terbuthylazine accounted for 0.9--1.2 percent of the initial radioactivity. In the soils studied, the extrapolated half-lives varied from 88 to 116 days for terbuthylazine and 66 to 105 days for atrazine, with no significant differences for the three soils and the two molecules. The deethyl metabolites of the two s-triazines and the deisopropyl-atrazine metaboliteappeared during the incubation in the three soils. The completely dealkylated metabolite was not detected in any of the soils. After 45 days of incubation, the non-extractable soil residues for the high clay, loamy clay and calcareous clay soils represented for terbuthylazine, 33.5, 38.3 and 43.1 percent and for atrazine, 19.8, 20.8 and 22.3 percent of the initial radioactivity. [ABSTRACT FROM AUTHOR]