USGS collected water samples nationwide from 182 streams and rivers during 19922001 and from 125 streams and rivers during 2002–2011. USGS collected the samples throughout the year, including during both high-flow and low-flow conditions. Sampling was most intensive during the time of highest pesticide use and runoff— generally weekly or twice monthly for a 4- to 9-month period.
|Copyright Michael R. Martin|
The level of pesticides in water is largely influenced by the surrounding land uses. Water analyses showed that the proportion of streams with one or more pesticides exceeding an aquatic life benchmark was similar between the two decades for streams and rivers draining agricultural and mixed-land use areas, but much greater during the 2002–2011 period for streams draining urban areas. Exceedances in urban streams increased from 53 percent during the first decade of monitoring to 90 percent during the second decade, largely as a result of the greater presence of fipronil and dichlorvos.
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