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Persistent Pesticides Detected in Groundwater Again

(Beyond Pesticides, October 27, 2008) Six pesticides that threaten water quality and public health continue to be detected in groundwater samples, according to a new U.S. Geological Survey (USGS) study. Published in the Journal of Environmental Quality, the study evaluates groundwater contaminants from samples taken from over 300 wells across the U.S. 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.

Original samples were taken from the wells from 1993-1995, and compared with samples taken from 2001-2003. Laboratory analysis was performed using methods that allowed detection of pesticide compounds at concentrations as small as 1,000 times below U.S. EPA drinking-water standards. Of the 80 compounds studied, six were detected in ground water from at least 10 wells during both of those sample periods. The six pesticide compounds detected are the triazine herbicides atrazine, simazine, and prometon; the acetanilide herbicide metolachlor; the urea herbicide tebuthiuron; and an atrazine degradate, deethylatrazine (DEA). Concentrations of these compounds generally were less than 0.12 parts per billion, or over 10 times lower than U.S. EPA drinking-water standards.

This is not reassuring considering the fact that many of the developmental impacts linked to atrazine are seen at very low levels, sometimes at just a fraction of a part per billion. It is the ubiquitous nature of the contamination rather than the concentration of these pesticide compounds that worries public health scientist and environmentalist. Research by Tyrone Hayes, Ph.D., a professor of Integrative Biology at the University of California, Berkeley, has found pesticides, including atrazine, to cause serious deformities at levels well below U.S. EPA drinking water standards. His research shows that 0.1 parts per billion of atrazine in the water where a frog develops can hermaphrodize the animal (having both male and female gonads). Even concentrations of a few parts per trillion can seriously impact the way an animal develops. A recent study links atrazine with endocrine disruption in both fish and human cells. The University of Califonia, San Francisco (UCSF) research examines the reaction of zebrafish to environmentally relevant levels of atrazine, and mirrors the study in human placental cells.

Atrazine is the second most commonly used agricultural pesticide in the U.S., and the most commonly detected pesticide in rivers, streams and wells. It is linked to endocrine disruption, neuropathy and cancer and has been banned by the European Union. An estimated 76.4 million pounds of atrazine are applied in the U.S. annually. Atrazine has a tendency to persist in soils and move with water, making it a very common water contaminant. Chronically contaminated drinking water puts humans at the risk of exposure to long-term health effects.

According to the study authors, 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 study is a part of USGS’ federally-funded National Water-Quality Assessment (NAWQA) Program, which 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.

This new study builds on the existing body of evidence that pesticides are contaminating our nation’s water resources. In July 2008, the results of another USGS study investigating the occurrence of selected pesticides and their degradation products in groundwater shows that pesticides can persist for years, depending upon the chemical structure of the compounds and the environmental conditions. The study reveals that the pesticides and degradation products detected most frequently in shallow ground water samples are predominantly from two classes of herbicides: triazines and chloroacetanilides. According to the Minnesota Department of Agriculture’s 2007 Water Quality Monitoring Report, released in August 2008, atrazine and metolachlor are detected in pristine lakes in northern Minnesota far from the agricultural fields where it is applied. In 2006, USGS released Pesticides in the Nation’s Streams and Ground Water, 1992-2001, a ten-year survey of the contamination caused by pesticide use in agricultural and urbanized areas. Every year, nearly one billion pounds of pesticides, many of which are linked to cancer, birth defects, neurological disorders, and environmental impacts, are used in the U.S, much of it ending up in our nation’s waterways. Two years earlier, according to Water Quality in the Nation’s Streams and Aquifers-Overview of Selected Findings, 1991-2001, released in 2004 as a compendium of 51 USGS reports on the health of major river basins across the country, insecticides such as diazinon and malathion were found in nearly all of the streams that were sampled in urban areas. Streams in agricultural areas were more likely to contain herbicides, especially atrazine, metolachlor, alachlor, and cyanazine. The United States Department of Agriculture’s Pesticide Data Program annual summary detailing pesticide residues in the U.S. food supply, reveals that among many pesticides detected, atrazine, metolachlor, and prometon were found in over half of the treated drinking water samples.

Looking for a positive spin, the study results show that the contamination levels of the nation’s groundwater supply is not increasing, even though more than one billion pounds of pesticide active ingredients are used annually in the U.S. “The results of this study are encouraging for the future state of the nation’s ground-water quality with respect to pesticides,” said 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.”

Water is the most basic building block of life. Clean water is essential for human health, wildlife, and a balanced environment. According to a Beyond Pesticides report, Threatened Waters: Turning the Tide on Pesticide Contamination, over 50% of the U.S. population draws its drinking water supply from ground water, which includes sources below the earth’s surface, including springs, wells, and aquifers. Once groundwater has been contaminated, it takes many years or even decades to recover, while streams and shallow water sources can recover much more rapidly. Herbicides are found more often in ground water than insecticides, but insecticides in ground water exceed drinking water standards more often than herbicides.

For more information on issues related to pesticides and water, see Beyond Pesticides’ Daily News Blog.


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