DEGRADATION AND BOUND RESIDUE FORMATION OF 4 ATRAZINE METABOLITES, DEETHYLATRAZINE, DEISOPROPYLATRAZINE, DEALKYLATRAZINE AND HYDROXYATRAZINE, IN A WESTERN TENNESSEE SOIL

Atrazine (2-chloro-4-[ethylamino]-6-[isopropylamino]-1,3,5-triazine) can be degraded to several metabolites in soil that include the dealkylated metabolites, deethylatrazine (DEA), deisopropylatrazine (DIA) and dealkylatrazine (DAA), and the dechlorinated metabolite, hydroxyatrazine (HYA). Biological and physical degradation and soil-bound residue formation from uniformly C-14 ring-labeled DEA, DIA, DAA and HYA were characterized in a western Tennessee soil using intact surface soil core microcosms. Metabolites were applied to soil microcosms at a rate of 0.5 kg/ha (approximately 1.2-mu-g/g soil). Concentrations of the dealkylated metabolites in nonirradiated soil microcosms decreased to less than 2% of the applied compound or were not detected after 180 d incubation. Hydroxyatrazine residues decreased to 33% of the applied concentration. In nonirradiated microcosms after 180 d, evolution of (CO2)-C-14 from radiolabeled DEA, DIA, DAA and HYA increased to 25, 16, 59 and 21%, respectively, of the total radiolabel added. Irradiated soil microcosms evolved 0.6, 1.7, 0.1 and 0.9%, respectively, of the total radiolabel added. Rates of dissipation for the four metabolites followed first-order kinetics. Half-lives for the dealkylated metabolites, based on extractable residues, ranged from 17 to 26 d, whereas HYA was 121 d. Soil-bound C-14 residues increased in concentration in nonirradiated microcosms and ranged from 28% of the applied radiolabel for HYA to 60% for DEA after 180 d. In irradiated microcosms the range was from 24% for HYA to 72% for DAA on day 180. Extractable C-14 residues in all microcosms decreased in concentration during this study and, after 180 d, ranged from 4% of the radioactivity added for DAA to 40% for HYA. Extractable C-14 residues in irradiated microcosms ranged from 31% of the initial activity for DAA to 68% for HYA at the termination of the study.