Experimental and Sample Processing Techniques for Aquatic Pesticide Dissipation Studies As a Seed-Treatment for Rice.

Field dissipation studies assessing pesticide fate are required as part of EPA’s data requirements to support the registration of pesticides. In a typical field dissipation study with a test substance applied as a broadcast application, a uniform distribution of test substance for representative soil-core sampling can be achieved by simply following proper calibration methods for applicators. Achieving uniform distribution of test substance for representative soil sampling may be, however, challenging in cases when the test substance is applied as seed treatment in rice that are flown onto flooded fields. Also, ensuring uniform mixing and homogenization of soil-core samples for such cases may be challenging because in seed treatment, compared to a broadcast application, the test substance is applied in a much smaller area relative to volume of the soil-core. Our objectives are to share: 1) experimental procedures helpful in achieving uniform distribution of a test substance for representative soil sampling in such studies, and 2) milling and homogenization techniques that aid in ensuring uniform mixing and homogenization of soil cores for representative aliquots (sub-samples) for residue analysis. The experimental and soil processing procedures have been successfully applied in our recent aquatic field dissipation studies of seed treated pesticides under water-seeded rice production conditions conducted in two rice producing regions of the USA, and are expected to be helpful guides for people engaged in regulatory field dissipation studies.