For release: March 3, 2006
Contact: Robert Gilliom (Lead author)
916-278-3094
Donna Myers
(NAWQA program coordinator)
703-648-5012
A.B. Wade (Press office)
703-477-2851
Today, the U.S. Geological Survey released a report describing the occurrence of
pesticides in streams and ground water during 1992-2001. The report concludes
that pesticides are typically present throughout the year in most streams in
urban and agricultural areas of the Nation, but are less common in ground water.
The report also concludes that pesticides are seldom at concentrations
likely to affect humans. However in many streams, particularly those
draining urban and agricultural areas, pesticides were found at concentrations
that may affect aquatic life or fish-eating wildlife.
Dr. Robert Hirsch, Associate Director for Water, said, “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.” Hirsch also commented that “the
USGS assessment 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 findings show strong relations between the occurrence of pesticides and
their use, and point out that some of the frequently detected pesticides,
including the insecticide diazinon and the herbicides alachlor and cyanazine,
are declining.
USGS has worked closely with the U.S. Environmental Protection Agency (EPA)
during the 10-year study. EPA uses the data extensively in their exposure
and risk assessments for regulating the use of pesticides. For example, EPA used
USGS data in its risk assessments for the reevaluation of diazinon, chlorpyrifos,
cyanazine and alachlor. Uses of three of these pesticides (diazinon,
chlorpyrifos and cyanazine) have now been significantly limited, and usage of
alachlor was voluntarily reduced and largely replaced by a registered
alternative.
The USGS report is based on analysis of data collected from 51 major river
basins and aquifer systems across the Nation from Florida to the Pacific
Northwest and including Hawaii and Alaska, plus a regional study in the High
Plains aquifer system.
Although none of the USGS stream sampling sites were located at drinking-water
intakes, a screening-level assessment was done by USGS to provide an initial
perspective on the relevance of the pesticide concentrations to human health.
USGS measurements were compared to EPA drinking-water standards and guidelines.
Concentrations of individual pesticides were almost always lower than the
standards and guidelines, representing less than 10 percent of the sampled
stream sites and about 1 percent of domestic and public-supply wells.
However, pesticides may have substantially greater effects on aquatic ecosystems
than on humans based on a screening-level comparison of USGS measurements to
water-quality benchmarks for aquatic life and fish-eating wildlife. 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.
Water-quality benchmarks are estimates of concentrations above which
pesticides may have adverse effects on human health, aquatic life, or
fish-eating wildlife.
Insecticides, particularly diazinon, chlorpyrifos, and malathion frequently
exceeded aquatic-life benchmarks in urban streams. 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 data indicate that
concentrations of these pesticides may have been declining in some urban streams
even before 2001—benchmark exceedences in urban streams were least frequent
late in the study. A case study of diazinon shows declining concentrations
in several urban streams in the Northeast during 1998-2004.
In agricultural streams, the pesticides chlorpyrifos, azinphos-methyl, p,p'-DDE,
and alachlor were among those most often found at concentrations that may affect
aquatic life, with each being most important in areas where its use on crops is
or was greatest. According to senior author Robert Gilliom, however,
“Pesticide use is constantly changing in response to such factors as
regulations and market forces and findings from this decade-long study need to
be examined in relation to changes in use during and after the study. For
example, levels of the herbicide alachlor declined in streams in the Corn Belt
(generally including Illinois, Indiana, Iowa, Nebraska, and Ohio, as well as
parts of adjoining states) throughout the study period as its use on corn and
soybeans declined, with no levels greater than its aquatic-life benchmark by the
end of the study. In contrast, both the use and the levels of atrazine,
the most heavily used herbicide in the Corn Belt region, remained relatively
high throughout the study period.”
In addition, DDT, dieldrin, and chlordane—organochlorine pesticide compounds
that were no longer in use when the study began—were frequently detected in
bed sediment and fish in urban and agricultural areas. Concentrations of these
compounds in fish declined following reductions in their use during the 1960s
and elimination of all uses in the 1970s and 1980s, and continue to slowly
decline. Just as notable as the declines, however, is the finding that these
persistent organochlorine pesticides still occur at levels greater than
benchmarks for aquatic life and fish-eating wildlife in many urban and
agricultural streams across the Nation.
The USGS study also reported that pesticides seldom occurred alone—but almost
always as complex mixtures. Most stream samples and about half of the well
samples contained two or more pesticides, and frequently more.
Gilliom explained that “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. 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.”
The report, “Pesticides in the Nation’s Streams and Ground Water,
1992-2001,” Circular 1291 is available at http://water.usgs.gov/pubs/circ./circ1291,
or by calling 1-888-ASK-USGS, or by fax 303-202-4693. In-depth information about
the pesticide assessment may be found at: http://water.usgs.gov/nawqa/
under “What’s New.”
The USGS serves the Nation by providing reliable scientific information to
describe and understand the Earth; minimize loss of life and property from
natural disasters; manage water, biological, energy and mineral resources; and
enhance and protect our quality of life.
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Karen Wood
Public Affairs Specialist
U.S. Geological Survey, Office of Communications
703-648-4447
Fax: 703-648-4466
Email: kwood@usgs.gov