REDUCTION OF NONPOINT-SOURCE CONTAMINATION OF SURFACE-WATER AND GROUNDWATER BY STARCH ENCAPSULATION OF HERBICIDES

The loss of the preemergent herbicide atrazine in surface runoff from experimental field plots growing com (Zea mays L.) was significantly reduced using a starch-encapsulated formulation versus a conventional powdered formulation. Field edge losses of starch-encapsulated atrazine were described as following a Rayleigh distribution totaling 1.8 % of applied herbicide compared to exponential powdered atrazine losses of 2.9 % applied-a 40 % decrease. This has important implications for the reduction of nonpoint source contamination of surface water by agricultural chemicals. Unsaturated zone release of starch-encapsulated atrazine was gradual, but comparable weed control was maintained. Deethylatrazine was a major dealkylated metabolite from each formulation, and deisopropylatrazine was a minor metabolite. The determination of soil partition coefficients for deethylatrazine and deisopropylatrazine (0.4 and 0.3, respectively), aqueous solubilities (3200 and 670 mg/L, respectively), and melting points (133 and 177-degrees-C, respectively) confirmed that the dealkylated metabolites should move more rapidly through the soil profile to groundwater than atrazine.