Pesticides in Runoff from Residential Homes in California

In many regions of the U.S., pesticides are frequently used by home owners and professional applicators for insect and weed control. Pesticides used at residential homes for structural pest control and landscape maintenance are suspected as an important cause for pesticide contamination of urban streams and estuaries in areas such as California. Researchers from University of California have undertaken a statewide project to understand the nature and magnitude of pesticide runoff from single family homes. Water samples have been collected on a weekly or biweekly basis from 8 neighborhoods and analyzed for a range of pesticides. Data so far show that pyrethroid insecticides and fipronil, both considered as replacements to organophosphate products, are ubiquitously present in both irrigation and rain induced runoff. Among the pyrethroid compounds, bifenthrin, cyfluthrin and permethrin are most frequently detected, and the combined concentrations suggest acute toxicity to aquatic invertebrates. Fipronil, a newly registered compound used mainly for termite and ant control, is also consistently present. Occurrence of these pesticides appears to correlate well with the use patterns and climate conditions, and is associated with the level of suspended solids. Findings from this study point to the need to develop guidelines and practices aiming to minimize pesticide export from residential areas to urban waterbodies.