Pesticides in U.S. Water
September 15, 1999
Streams in areas with significant agricultural or urban development
almost always contain complex mixtures of nutrients and pesticides,
according to a report released by the U.S. Geological Survey (USGS).
The report, "The Quality of Our Nation's Waters," looks at water
quality in 20 of the largest and most important river basins in the
United States. Researchers found 83 pesticides and breakdown products
in water and 32 pesticides in fish or streambed sediment. Although the
study targeted the broadest and most complete range of pesticides ever
measured in a single assessment, researchers were not able to test for
many important pesticide compounds because of analytical and budget
constraints. Pesticides not measured include glyphosate, acephate,
dimethoate, methomyl and thiodicarb.
The report documents that concentrations of individual pesticides in
samples from wells and as annual averages in streams were almost
always lower than current U.S. Environmental Protection Agency
(EPA) drinking-water standards and guidelines. However, more than
one half of the streams sampled had concentrations of at least one
pesticide that exceeded a guideline for protection of aquatic life.
According to USGS, the potential risk to people and to aquatic life can
only be partially addressed based on available standards and guidelines.
The health picture is made more complex by the lack of standards or
guidelines for many pesticides and their breakdown products or
metabolites. Currently EPA has established standards and guidelines
for only 46 of the 83 pesticides and breakdown products measured in
this study. Of the thousands of possible pesticide breakdown products,
few have been looked for in streams or ground water.
Adding to the complexity is the fact that existing standards were
developed for individual chemicals and do not take into account
exposure to mixtures of chemicals and seasonal pulses of high
concentrations. The USGS analysis detected two or more pesticides in
almost every stream sample and about one-half of the well samples.
Some of the most frequently detected pesticides are suspected
endocrine disrupters that may affect reproduction or development of
aquatic organisms or wildlife by interfering with natural hormones.
Some of the highest concentrations of nitrogen and herbicides,
including those most heavily used (such as atrazine, metolachlor,
alachlor and cyanazine) were detected in USGS samples collected from
streams and shallow ground water in agricultural areas. Some of the
highest concentrations of phosphorus and insecticides (including
diazinon, carbaryl and malathion) were found in urban streams. Of the
urban streams studied by the USGS, nearly every one had
concentrations of insecticides that exceed guidelines for protection of
aquatic life.
Contaminants found in the USGS study include chemicals that are no
longer in use, such as DDT, which was banned in the early 1970s.
Persistent insecticides, such as the organochlorines DDT, dieldren and
chlordane, are still found at elevated levels in fish and streambed
sediment in many urban and agricultural streams across the United
States. Although still present, there has been a reduction in
concentrations of dieldrin and chlordane insecticides in whole fish
since the 1980s, and concentrations of DDT in sediments have also
decreased.
The USGS report shows that understanding patterns of contamination
in relation to land use, pesticide use and the natural characteristics of
hydrologic systems can potentially help reduce the amounts of
pesticides that reach streams and ground water. It calls for local and
regional management strategies to account for geographic patterns in
land use, chemical use and natural factors.
"The Quality of Our Nation's Waters--Nutrients and Pesticides," USGS
Circular 1225, is available as a PDF file on the USGS Web site:
http://water.usgs.gov/pubs/ circ/circ1225/ or in printed form (single
copies free) from: Branch of Information Services, P.O. Box 25286,
Denver, CO 80225 or fax request to (303) 202-4693. Please specify
USGS report C-1225.
For more information, visit the USGS pesticide home page at
http://water.wr.usgs.ogv/pnsp -- includes pesticide data, maps and other
pesticide publications.
Sources: U.S. Geological Survey News Release, June 28, 1999, and
"The Quality of Our Nation's Waters," USGS, May 1999.
Contact: NAWQA Program, USGS, 413 National Center, Reston, VA
20192; phone (703) 648-5716; fax (703) 648-6693; email
nawqu_whq@usgs.gov.
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