A new interactive mapping tool created by the US Geological Survey provides predicted concentrations for 108 pesticides in streams and rivers and identifies which are most likely to exceed water-quality guidelines for human health or aquatic life.

The tool allows users to create maps showing where pesticides are likely to occur in local streams and rivers and evaluate the likelihood of concentrations exceeding water-quality guidelines.  The predictions can also be used to design cost-effective monitoring programs.

“Because pesticide monitoring is very expensive, we cannot afford to directly measure pesticides in all streams and rivers,” said William Werkeiser, USGS Associate Director for Water.  “This model can be used to estimate pesticide levels at unmonitored locations to provide a national assessment of pesticide occurrence.”

“The USGS pesticide model is a valuable tool that we can use, along with other modeling and analytical tools, to evaluate data as we complete ecological risk assessments for pesticides,” said Dr. Donald J. Brady, Director, Environmental Fate and Effects Division, Office of Pesticide Programs, U.S. Environmental Protection Agency.

Wes Stone, USGS hydrologist and lead developer of the model  said that streams and rivers most vulnerable to pesticides can be assessed, citing the example of many streams in the Corn Belt region which are predicted to have a greater than 50% probability that one or more pesticides exceed aquatic-life benchmarks.

The online mapping tool is based on a USGS statistical model — referred to as Watershed Regression for Pesticides (WARP) — which provides key statistics for thousands of streams, including the probability that a pesticide may exceed a water-quality benchmark and the reliability of each prediction.

The WARP model estimates concentrations using information on the physical and chemical properties of pesticides, agricultural pesticide use, soil characteristics, hydrology, and climate. 

The model used by the mapping tool is based on data from USGS monitoring of pesticides in streams across the USA since 1992 as part of the National Water-Quality Assessment (NAWQA) Program.

Since 1991, NAWQA has been a primary source of nationally consistent data and information on the quality of the nation’s streams and groundwater.

Interactive mapping of predicted pesticide levels for streams in the U.S. are available online. National maps and trend graphs of agricultural use of 459 pesticides from 1992 to 2012 are also available online.

The pesticide-use maps show the geographic distribution of estimated use on agricultural land in the United States for numerous pesticides. Maps were created by allocating county-level use estimates to agricultural land within each county. A graph accompanies each map, which shows annual national use by major crop for the mapped pesticide for each year during the period.

Click here to access the tool online