Pesticides in the Nation ?s Streams and Ground Water

[Karen Renee Wood <kwood@xxxxxxxx>]

News Release

U.S. Department of the Interior
U.S. Geological Survey

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


Pesticides in the Nation’s Streams
and Ground Water

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@xxxxxxxx