DEGRADATION OF [C-14] TERBUTHYLAZINE AND [C-14] ATRAZINE IN LABORATORY SOIL MICROCOSMS

The degradation and formation of major chlorinated metabolites of terb uthylazine and atrazine in three soils (loamy clay, calcareous clay an d high clay) were studied in laboratory experiments using molecules la belled with C-14 on the s-triazine ring. Soil microcosms were treated with the equivalent of 1 kg ha(-1) of herbicide and incubated in the d ark for 45 days at 20(+/-1)degrees C. The quantity of [C-14]carbon dio xide evolved in the soils treated with atrazine was negligible and cou ld not be attributed to mineralization of the parent molecule. The min eralization of terbuthylazine accounted for 0.9-1.2% of the initial ra dioactivity. In the sc,ils studied, the extrapolated half-lives varied from 88 to 116 days for terbuthylazine and 66 to 105 days for atrazin e, with no significant differences for the three soils and the two mol ecules. The deethyl metabolites of the two s-triazines and the deisopr opyl-atrazine metabolite appeared during the incubation in the three s oils. The completely dealkylated metabolite was not detected in any of the soils. After 45 days of incubation, the non-extractable soil resi dues for the high clay, loamy clay and calcareous clay soils represent ed for terbuthylazine, 33.5, 38.3 and 43.1% and for atrazine, 19.8, 20 .8 and 22.3% of the initial radioactivity.