ATRAZINE DEGRADATION AND RESIDUE DISTRIBUTION IN SOIL

Degradation and its effect on atrazine leaching were observed in soil in the laboratory. Degradation of 1.5 ppmw (wt/wt) of ring labeled 14C-atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) over time periods up to 8 months was predominantly a nonbiological process in three nonsterilized soils at 0.1 bar moisture content, although there was evidence that the atrazine molecule was dealkylated simultaneously. Between 4 and 17% of the applied 14C was present as nonpolar compounds after 1 month of incubation at 30°C. The amount of 14CO2 evolved was cumulatively less than 0.05% of the added radiocarbon at 5 and 30°C. Desorption of atrazine from soil treated and incubated for 0.5 hour; 1 and 2 weeks; 1, 2, 4, and 8 months showed a steady increase in the unextractable fraction remaining in soil with time. In the soil extract, a toluene-insoluble fraction increased as time passed, and made up between 24 and 62% of the extracted radiolabeled fraction of the three soils after 1 month of incubation at 30°C. The ratio of polar compounds to nonpolar compounds steadily increased with time of incubation. Major possible metabolites of the toluene-soluble fraction were identified by thin layer chromatography as monodealkylated products. During elution of atrazine from soil columns saturated with water, decreasing the water flow rate from 2 cm/hour to 0.08 and 0.04 cm/hour greatly reduced the downward movement and enhanced degradation of the herbicide.