The widespread use of pesticides across the United
States has been in practice for decades, with little knowledge of the long-term
effects on the nation’s ground water.
The results of a new study show that samples taken
from more than 300 wells across the United States have not retained a high
concentration of pesticide contamination. The news is a result of a decadal
long study to assess the extent of the impact of contaminants on the nation’s
water supply.
Over the years, frequent research has detected
pesticides in ground water around the country, including in aquifers used for
drinking-water supply. Over the past few decades, the use of some pesticides
has been restricted or banned, while new pesticides have been introduced. One
goal of the study was to track the retention of various types of contaminants
that would be found in the different pesticides used over the years.
Results for one of the first national studies on
the presence of pesticides in ground water recently were published by the U.S.
Geological Survey (USGS), as a part of
that agency’s federally funded National Water-Quality Assessment (NAWQA)
Program.
“The results of this study are encouraging for the
future state of the nation’s ground water quality with respect to pesticides,” says
Laura Bexfield, who conducted the data analysis. “Despite sustained use of many
popular pesticides and the introduction of new ones, results as a whole did not
indicate increasing detection rates or concentrations in shallow or
drinking-water resources over the 10 years studied.”
Original samples were taken from the wells from
1993 to 1995, and compared with samples taken from 2001 to 2003. Laboratory
analysis was performed using methods that allowed detection of pesticide
compounds at concentrations as small as 1,000 times below U.S. Environmental
Protection Agency (EPA) drinking-water standards. Of the 80 compounds studied,
only six were detected in ground water from at least 10 wells during both of
those sample periods. Concentrations of these compounds generally were less
than 0.12 parts per billion, or more than 10 times lower than applicable EPA
drinking-water standards.
Characterization of trends in pesticide
occurrence and concentrations through time is important in determining how
quickly ground water systems respond to changes in chemical use and in
identifying compounds that may pose a threat to water quality before
large-scale problems occur. Continuing research is planned to track and
understand changes in both ground and surface-water quality across the United
States.
The NAWQA is an ongoing USGS program that provides
an understanding of water-quality conditions and how those conditions may vary
locally, regionally and nationally; whether conditions are getting better or
worse over time; and how natural features and human activities affect those
conditions.