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U.S.: Most rivers, streams have pesticides

Pesticides linked to cancer, birth defects and neurological disorders pollute almost all of the nation’s rivers, and while concentrations seldom threaten humans they are often a threat to wildlife, government scientists said Friday.
Bread and Oil: California's Central Valley
Farm workers spray chemicals at the edge of a field bordering homes in Lamont, Calif, in this 2004 photo. David Mcnew / Getty Images file
/ Source: staff and news service reports

Pesticides linked to cancer, birth defects and neurological disorders contaminate almost all of the nation’s rivers and streams, and while concentrations are at levels that seldom threaten humans they are often a threat to wildlife, government scientists said Friday.

Though the pesticides were less common in ground water, the U.S. Geological Survey’s study of data between 1992 and 2001 found them present in streams in both urban and agricultural areas at concentrations that could affect aquatic life or fish-eating wildlife.

Robert Hirsch, the USGS associate director for water, said in a statement that “while the use of pesticides has resulted in a wide range of benefits to control weeds, insects, and other pests, including increased food production and reduction of insect-borne disease, their use also raises questions about possible effects on the environment, including water quality.”

About 40 pesticides of 100 that were studied accounted for most of the findings in water, fish and sediment. Three herbicides used mainly on farms, atrazine, metolachlor, and cyanazine, were the most frequently detected in agricultural streams. Three herbicides used commonly in cities, simazine, prometon, and tebuthiuron, showed up more often in urban streams.

The pesticides also showed up more than 90 percent of the time in the fish tissue found in agricultural, urban and mixed land-use areas.

At least one pesticide was detected in water from all the streams studied. Pesticide compounds were found at nearly all times of the year in about 19 of every 20 streams with agricultural, urban or mixed land-use watersheds, the agency said. The most frequent occurrence was in shallow ground water beneath agricultural and urban areas, where more than half the wells contained one or more pesticide compounds.

Hirsch said the study “provides the most comprehensive national-scale analysis to date of pesticide occurrence in streams and ground water. Findings show where, when, and why specific pesticides occur, and yield science-based implications for assessing and managing pesticides in our water resources.”  

The USGS, in the statement, said that “more than 80 percent of urban streams and more than 50 percent of agricultural streams had concentrations in water of at least one pesticide —mostly those in use during the study period — that exceeded a water-quality benchmark for aquatic life.”

But it also noted that “most urban uses of diazinon and chlorpyrifos, such as on lawns and gardens, have been phased out since 2001 because of use restrictions imposed by the EPA.”

The USGS report is based on an analysis of data from 51 major river basins and aquifer systems nationally, and a study of an aquifer system that runs through eight states from South Dakota to Texas, east of the Rocky Mountains.

It found that concentrations of individual pesticides nearly always complied with Environmental Protection Agency drinking-water standards, though no water samples from streams were taken at drinking-water intakes.

EPA also is responsible for reviewing pesticides, based on pesticide-makers’ tests that can cost tens of millions of dollars. It typically takes up to a decade to study each one before it can reach the marketplace, according to industry figures.

‘Pesticide mixtures’ a concern
The USGS study also found that most stream samples and about half of the well samples contained two or more pesticides, and frequently more.

“The potential effects of contaminant mixtures on people, aquatic life, and fish-eating wildlife are still poorly understood and most toxicity information, as well as the water-quality benchmarks used in this study, has been developed for individual chemicals,” said USGS scientist and lead author Robert Gilliom.

“The common occurrence of pesticide mixtures, particularly in streams, means that the total combined toxicity of pesticides in water, sediment, and fish may be greater than that of any single pesticide compound that is present. Studies of the effects of mixtures are still in the early stages, and it may take years for researchers to attain major advances in understanding the actual potential for effects. Our results indicate, however, that studies of mixtures should be a high priority.”

Industry perspective
But simply detecting the presence of a pesticide does not always mean there is reason for concern, said Jay Vroom, president of CropLife America, which represents pesticide developers and manufacturers.

He emphasized that the use of pesticides by farmers, ranchers and others is strictly regulated by federal and state laws.

“Water quality is of paramount importance to us,” he said. “And the USGS report correctly recognizes that the large majority of pesticide detections in streams and groundwater were trace amounts, far below scientifically based minimum levels set for protecting human health and the environment.”

The full USGS report is online at