Fipronil Monitoring and Model Scenarios
Abstract
The California Department of Pesticide Regulation (DPR) Surface Water Protection Program (SWPP) has identified fipronil as a contaminant of concern in California surface waters. Fipronil has been detected in approximately half of all monitoring samples at concentrations above toxicity thresholds set by the US Environmental Protection Agency (USEPA). Currently there are two fipronil-containing products registered in California that have been identified as contributing to urban runoff concentrations. Presented is a modeling approach to evaluate the effects of altering application practices with the potential to reduce fipronil runoff from residential areas of California. Using the USEPA acute benchmark as a reduction goal, fipronil concentrations in urban receiving waters of California would need to be reduced by 59% (based on monitoring results) to 78% (based on modeling results). Tested scenarios include narrow application band, reduction of fipronil mass applied, and restriction of areas that can be treated. Less applied mass with narrow band proportionally reduces fipronil urban runoff. For example, model-predicted fipronil concentration in urban receiving water is reduced by 92% with “one-inch up and one-inch out” using pin stream application, compared to label-suggested band of one foot. In addition, fipronil runoff potential is sensitive to applications to the garage door/driveway interface. Exclusion of driveway/garage door uses results in concentration reduction by 43%, while the applied mass is only decreased by 16%. A research contract with the University of California at Riverside has been initiated to test modeled application scenarios on runoff potential and bioefficacy.