Estimating pesticide concentrations in U.S. streams from watershed characteristics and pesticide properties

AGRO 140

Charles G. Crawford and Robert J. Gilliom. U.S. Geological Survey, 5957 Lakeside Boulevard, Indianapolis, IN 46278
Empirical regression models have been developed by the U.S. Geological Survey for estimating the concentration of atrazine in streams from pesticide-use intensity and various watershed characteristics. Separate models were developed to estimate the time-weighted annual mean and selected percentile concentrations (the 5th, 10th, 15th, 25th, 50th, 75th, 85th, 90th, and 95th). The models were developed from monitoring data collected at more than 100 streams throughout the United States as part of the U.S. Geological Survey's National Water-Quality Assessment (NAWQA) Program. Pesticide use in a watershed was the most significant explanatory variable, but several hydrologic and soil parameters were useful in explaining the variability in observed atrazine concentrations. The atrazine models have been extended to other pesticides by an adjustment factor that incorporates pesticide properties. Predicted concentrations were nearly always within an order of magnitude of the measured concentrations, and the predicted percentile concentrations reasonably matched the actual distribution of the percentiles in most cases. The models can be used for human-health risk assessments by estimating concentrations of pesticides in streams used for drinking-water supply or designing monitoring programs for ecological risk assessments by identifying streams with concentrations exceeding a level of concern.