CONTROLLED RELEASE FORMULATIONS OF ATRAZINE IN STARCH FOR POTENTIAL REDUCTION OF GROUNDWATER POLLUTION

The availability of the herbicide atrazine [2-chloro-4-ethylamino-6-isopropylamino-s-triazine to a soil-water system was greatly diminished by entrapping the herbicide in starch granules. Factors influencing the preparation of and release from these granules were determined. The delivery of atrazine from the granules to a soil-water system was compared with delivery to water. Availability of atrazine from unentrapped commercially available atrazine was also determined. In 15 minute soil-water tests, the rate of delivery of atrazine at a constant level of active ingredient increased as the surface area available in the formulations increased, which was made possible by decreasing the loading, by making the granules smaller, and by improving the degree of atrazine dispersion during granule formulation. Aging of the starch formulations from one to nine days diminished atrazine release. When the soil-water tests were conducted over 20 days, the larger granules (14-20 mesh), as a result of the smaller sample size, released atrazine slower than smaller granules (20-40 mesh). The larger granules induced 35% of saturation in 6 days and the smaller induced 45% of saturation in 3 days. Controlled release over these intervals was proportional to the square root of time according to the theory for controlled matrix diffusion. The larger granules kept in water under these conditions showed release to cause over 70% of saturation in 4 days and indicated that over 60% of the available atrazine was adsorbed by the soil. Atrazine present in saturated aqueous solutions was about 80% recoverable under the conditions of filtration and extraction. No controlled release was observed in soil-water mixtures. © 1990.