A national survey has found that pesticides are common year-round in streams across the United States. Only a few had levels that might be of concern to humans, but there is "widespread potential for adverse effects" for aquatic life, according to a report released today by the U.S. Geological Survey (USGS).
The data come from the USGS's National Water-Quality Assessment Program, which began monitoring 51 rivers and aquifers in 1992. Researchers visited 186 streams and 5000 wells across the country. They sampled water and sediments, charting levels of pesticides, trace metals, and other substances. For the current report, USGS analyzed data through 2001 which was the broadest extent of the program. They compared the levels of pesticides to health benchmarks based on toxicity standards from the Environmental Protection Agency.
Every stream had at least one pesticide at some time, and 10% had levels that exceeded the benchmark at which human health effects are possible. None of the measurements was made near intakes of drinking water supplies, but the report suggests it's unlikely that they exceed benchmarks because pesticides are typically not intense in these watersheds. The prevalence of pesticides was much lower in ground water; only 1.2% of wells exceeded the benchmark.
There is more concern for aquatic organisms and the wildlife that feed upon them. Of the 178 streams near farms or cities, 56% had one or more pesticides exceeding benchmarks. "Aquatic life in urban streams is particularly threatened," said report author Robert Gilliom, who leads the USGS's Pesticide National Synthesis Project Study Team.
The good news is that extent of the problem seems to be shrinking. Between 1993 and 1997, 95% of urban streams exceeded benchmarks for aquatic life. The number fell to 65% between 1998 and 2000.
The findings provide important data on pesticides, says Paul Schwartz of Clean Water Action, a nonprofit environmental group based in Washington, D.C. "This gives us food for thought about the complexities we're facing." In a press release, pesticide manufacturer Syngenta praised the "high quality monitoring techniques" but said that some of the benchmarks were outdated.