ECOLOGICAL RISK ASSESSMENT OF PESTICIDES ON MUSKRATS (ONDATRA-ZIBETHICUS) INHABITING AN AGRICULTURE AREA IN ILLINOIS, USA

A retrospective risk assessment was used to investigate whether pestic ide use adversely affected populations of muskrats (Ondatra zibethicus ), semi-aquatic mammals inhabiting agriculture drainage ditches in nor thwestern Illinois. Assessment endpoint benchmark concentrations in wa ter were calculated for muskrats from laboratory rat multiple-generati on reproduction no-observed-effect levels. The pesticide root zone mod el and exposure analysis modeling system simulated pesticide fate and revealed expected environmental concentrations (EECs) of pesticide in receiving water. The EECs following agriculture practices and meteorol ogic events typical of northern Illinois were below endpoint benchmark concentrations. A modeled worst-case scenario of exposure (three time s the typical application rates and 1 cm of rain on the day of applica tion) also revealed EECs below endpoint benchmarks. Assessment results suggested that muskrat populations in northern Illinois were not at r isk from the application of pesticides. Results from two other lines o f evidence further supported conclusions of this risk assessment.