Assessment of Risks Associated with Molinate Usage. R. C. Cochran, T. A. Formoli, J. M. Lee, and K. F. Pfeifer, Dept. of Pesticide Regulation, Cal. EPA, Sacramento, CA 95814
Molinate (S-ethyl hexahydro-1H-azepine-1-carbothioate) is a selective, pre-emergence, thiocarbamate herbicide registered in California for use on rice. Approximately 1.4 million pounds of molinate active ingredient were used in California in 1992. The majority of the products were applied by aerial spraying. The principal occupational exposures are to mixer/loaders, pilots, and flaggers. Biomonitoring procedures were used to determine the extent of these exposures. Non-occupational exposures were estimated from concentrations of molinate found in ambient air and water samples, using a series of default assumptions for breathing rates and water consumption. Examination of the toxicological information available on molinate indicated the most critical/sensitive toxicological endpoints of concern from repeated exposure to molinate were adverse reproductive effects and neurotoxicity. The application practices for molinate indicate that it is used only during a six week period in a given year. Therefore, the principal types of exposure, both occupational and non-occupational, are short-term and seasonal. Even though the use-season for molinate is limited to a 6-week period, some data suggest the neurotoxic effects of molinate may not be reversible. Consequently, theoretical annual occupational exposure was considered as well. The no-observed-effect-level (NOEL) used to calculate a margin of safety for potential short-term (acute) exposures to molinate was 11.5 mg/kg-day for reduced fertility in rats. A subchronic NOEL (0.48 mg/kg-day) for sperm abnormalities in rats was used as the basis for calculating margins of safety for potential seasonal exposures to molinate. A 1-year NOEL for neurotoxicity in the dog, 1 mg/kg-day for intermittent clinical signs (abnormal postural reactions) in dogs, was used to establish margins of safety for theoretical annual exposures to molinate.