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Tests Find Pesticides in Rural Wells: Private Water Treatment Encouraged

Posted on: Sunday, 16 April 2006, 06:00 CDT

By Frederick Melo, Pioneer Press, St. Paul, Minn.

Apr. 16--In rural Dakota County, tests have found trace elements of a surprisingly high number of pesticides in private wells, prompting calls from environmental officials for individual well owners to install home treatment systems.

"It's not an imminent health threat for today," said David Swenson, the county's environmental management supervisor. "It's a health threat if we continue down (this) road."

The 68 private well owners who participated in the study received letters from the county with their individual results last week. In May, all 8,000 private well owners in the county will receive a general letter describing the study results.

The study, believed to be the most comprehensive in the state, underscores the lingering environmental impact of farm chemicals on drinking water years after toxic pesticides were taken off the market.

The tainted wells are heavily clustered around Vermillion, Marshan and other rural, southeastern townships with a history of farming.

The county, which has monitored private bedrock wells for contaminants since 1999, has found elevated levels of nitrate in about half of the 68 wells tested. In up to 21 percent of the wells, nitrate levels regularly exceed drinking-water standards.

In 2004, the county expanded its testing to include private sand and gravel wells. It also began screening for a wider variety of pesticides and farm chemicals, such as cyanazine, a herbicide that has been banned since 2002.

"We were surprised to find (cyanazine) at all," said Jill Trescott, an environmental specialist with the county.

The results:

-- More than 60 percent of private wells that draw water from a sandstone aquifer had detectable levels of pesticides or their less-toxic breakdown products, although none exceeded state health standards.

-- In sand and gravel wells and limestone wells, about 80 percent had detectable pesticides. In about a fifth of the sand and gravel and limestone wells, traces of the herbicides cyanazine or alachlor exceeded the recommended drinking-water standard.

Nitrate, the most common form of groundwater contamination in Minnesota, comes from the nitrogen in fertilizer and human and animal waste, among other sources. The human body needs some nitrate to survive, but too much can affect health.

An infant fed water or formula with high nitrate levels can suffer a medical condition called "blue baby syndrome" (or methemoglobinemia), which may include skin discoloration and digestive and respiratory problems. Parents should not give water from wells with high nitrate levels to any infant younger than 6 months, either directly or in formula.

County officials warn residents not to boil water to "treat" high nitrate levels. Boiling actually concentrates the nitrate as the water evaporates. Pregnant women should avoid drinking well water with high nitrate levels.

In laboratory tests, cyanazine has been linked to birth defects in test animals, and alachlor has been linked to cancer.

County officials note that while farm fertilizers, pesticides and herbicides are likely to be blamed for groundwater contamination, farmers have made strides to reduce their dependency on these chemicals. Nonetheless, the testing shows they remain detectable in the environment long after they're taken out of general use.

"The farmers in this area are following the University of Minnesota best practices for agriculture," Swenson said. "They're not the bad guy. They're not doing anything wrong. However, it's the geology that's not cooperating."

Large pesticide molecules break down into smaller molecules, which are generally less toxic than the parent chemical but survive in the ecosystem longer. Samples from the private wells were tested for the presence of 15 pesticide parent compounds and 38 breakdown products; eight parent compounds and 28 breakdown products were detected.

In a separate study, municipal wells in Hastings also showed high levels of nitrate; a Hastings well that registered unexpectedly large traces of cyanazine has been shut down. The city is constructing a new well and treatment facility.

Municipal wells were not included in the study.

The groundwater study can be found online at www.dakotacounty.us./environ/water.htm.

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Copyright (c) 2006, Pioneer Press, St. Paul, Minn.

Distributed by Knight Ridder/Tribune Business News.

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Source: Saint Paul Pioneer Press (St. Paul, Minn.)

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