The U.S. Geological Survey recently published a comprehensive overview of pesticides in the nation’s streams and ground water. Water samples were collected at 186 streams in 51 study areas across the country and pesticides in ground water were monitored in over 5,000 wells.
The findings confirm earlier studies showing that pesticides have become ubiquitous contaminants throughout the hydrogeological cycle, especially in farming areas. Every stream sampled contained one or more positive sample. In agricultural areas, 97 percent of the samples had one or more pesticides. Over 90 percent of fish in farming regions had detectable levels of pesticides.
Just under 10 percent of all stream water samples in agricultural areas contained pesticides above “human-health benchmarks,” levels that are typically set by the EPA. Current pesticide levels pose greater risk to aquatic organisms. The USGS concluded that 57 percent of the samples in agricultural areas contained residues above aquatic organism health benchmarks.
Five of the most widely used herbicides were among the most commonly detected pesticides in streams and ground water – atrazine, metolachlor, cyanazine, alachlor, and acetochlor. The insecticides diazinon, chlorpyrifos, and carbaryl were also frequently detected.
Authors: Robert J. Gilliom, Jack Barbash, Charles Crawford, Pixie Hamilton, Jeffrey Martin, Naomi Nakagaki, Lisa Howell, Jonathan Scott, Paul Stackelberg, Gail Thelin, and David Wolock
USGS Circular No. 1291.