Assessment of Risks Associated with Diquat Dibromide. R. C. Cochran, T. A. Formoli, K. F. Pfeifer, and M. H. Silva, Dept. of Pesticide Regulation, Cal. EPA, Sacramento, CA 95814
Using the submitted and published toxicity database, estimates from monitoring information on diquat and surrogate exposure data, the initial margins of safety (MOSs) for potential short-term exposure diquat dibromide were less 100 for aquatic applicators and boat drivers using handguns, mixer/loaders and flaggers associated with aerial applications, ground applicators (except for hand applications on right-of-ways), and non-occupational exposures to drift at 50 meters. MOSs for potential annual occupational exposure to diquat for ground applicators using vehicles with normal clearance and no cab were also less than 100. Consequently, mitigation measures to reduce potential exposure were initially considered. However, the subsequent submission of a new single-dose dermal toxicity study in rabbits, and a biological monitoring study for occupational exposure in a particular work task caused a re-evaluation of the risks associated with the use of diquat dibromide. As most occupational and non-occupational exposures to diquat dibromide involved dermal absorption, the dermal NOEL (100 mg/kg for reduced food consumption and death in rabbits) was more applicable for assessing the risks of acute human exposure to diquat. The new, biological monitoring exposure study indicated that the amount of diquat absorbed by ground applicators was over 300 times less than the previous estimate, which was based on passive dosimetry. The combined effect of the two studies was to indicate no mitigation measures would be required.
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