USGS tallies the
extras in our water
Friday, July 2, 1999
Streams that pass through agricultural and
urban areas almost always contain complex mixtures of
nutrients and pesticides, but aquatic species are more at
risk than humans, according to a report released June 28 by
the U.S. Geological Survey.
The report, The
Quality of Our Nation's Waters — Nutrients and Pesticides,
is available on the World Wide Web.
The USGS studied water quality in 20 of
the country's largest and most important river basins and
aquifers. According to the report, samples from more than 50
percent of agricultural and urban streams had concentrations
of at least one pesticide that exceeded a guideline for
protecting aquatic life. The good news, according to the
study, is concentrations of individual pesticides were
almost always lower than current U.S. Environmental
Protection Agency drinking-water standards and guidelines.
In the aquatic environment, concentrations
of nitrogen and phosphorus commonly exceed levels that can
contribute to excessive growth of algae and other nuisance
plants in streams, according to the survey. According to the
USGS, such growth can clog water intake pipes and filters
and interfere with recreational activities, such as fishing,
swimming and boating. The subsequent decay of the algae can
result in foul odors, bad taste in drinking water and low
dissolved oxygen in aquatic habitats (oxygen that is
necessary for fish and other aquatic life to survive).
The complexities of the chemical mixtures
and the lack of current human and aquatic health standards
to determine risk of exposure to nutrients and pesticides
have made these issues a top national priority.
"Over the last two decades, our
nation has made great progress in improving water quality
and, yet, as the USGS report points out, major challenges
remain in protecting our aquatic resources," said
Secretary of the Interior Bruce Babbitt. "The
widespread occurrence of pesticides and nutrients in water
documented in the USGS report underscores the need to devote
more attention to the quality of our waterways and the life
that depends on them."
According to the USGS, the potential risk
to humans and aquatic life is based on available standards
and guidelines that don't provide the clearest picture.
Health implications are made more complex by the lack of
standards for many pesticides and their components. Existing
standards were developed for individual chemicals and don't
account for exposure to mixtures of chemicals and seasonal
changes resulting in high concentrations.
While USGS analysis of almost every stream
sample and about one-half of the well samples detected the
presence of two or more pesticides; this does not
necessarily equal harm to human or aquatic health, according
to USGS. The USGS uses a level of accuracy, sometimes parts
per trillion, that is well below the threshold used for
setting national standards and guidelines.
The USGS stated in its report that
understanding patterns of contamination in relation to land
use, pesticide use and the natural characteristics of
hydrologic systems can help reduce the amounts of pesticides
that reach streams and groundwater. Nearly every urban
stream studied showed concentrations of insecticides that
exceed guidelines for protection of aquatic life, which
shows water pollution is not just an agricultural problem.
"Despite considerable progress in the
four decades since Rachel Carson warned the nation of the
risks posed by environmental contaminants, a large range of
nutrients and other contaminants continue to enter our
waterways," said Mark Schaefer, deputy assistant
secretary for water and science at the Interior Department.
Even though DDT was banned in the early
1970s, the USGS studies still detected it in fish and
streambed sediment in many urban and agriculture streams in
the U.S. The concentrations had decreased, USGS said.
Copyright 1999,
Environmental News Network, All Rights Reserved
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