Potomac River Tap Water Has Small Levels of Contaminants

Tap water in the District and parts of Northern Virginia contains small amounts of herbicides, gasoline additives and industrial solvents -- although the concentrations are so small that there is probably no risk to consumers, according to a new federal study.

The U.S. Geological Survey measured water from the Washington Aqueduct, a federal agency that treats Potomac River water and sends it to the District, Arlington County and Falls Church. It found 17 chemical compounds that had escaped the treatment process, but in minuscule amounts, such as .258 parts per billion.

At those levels, "adverse effects to human health are expected to be negligible," the study says.

Tom Jacobus, general manager of the Washington Aqueduct, said none of these contaminants was found in an amount that violated standards set by the U.S. Environmental Protection Agency.

But scientists still have questions about the effects of some of the contaminants. One, the weedkiller atrazine, is being examined as a possible cause of the Potomac's "intersex" bass -- male fish that have begun growing eggs.

"Unfortunately, you know, we just don't know right now" whether humans could be harmed by long-term exposure to the chemical, said Vicki S. Blazer, a Geological Survey scientist who has studied the intersex fish. She was not an author of the tap-water study. "There's little known about effects on aquatic animals and even less on humans."

The research on the Potomac was part of a larger project that measured contaminants in tap water at nine sites across the country. The Geological Survey found chemicals from every corner of life -- from pest-killers to artificial fragrances to caffeine.

Michael Brayton, a scientist who worked on the study, said these chemicals either washed off the land or were discharged in treated sewage. They wound up in lakes or streams, then in intake pipes for drinking-water plants. The processes used to treat that water kill bacteria but often miss the traces of these contaminants.

"Treatment plants around the country are not designed to treat for these," Brayton said. He said the contaminants found in the District's drinking water were often found elsewhere.

In addition to atrazine, tests on the Washington Aqueduct's water found the herbicides metolachlor and simazine. They also found an industrial fragrance called HHCB, the gasoline additive MTBE, and the solvents carbon tetrachloride and methylene chloride.

Jacobus said consumers do not need to filter or otherwise treat their tap water to remove them. "We're interested in this," he said. "But we're not alarmed."

But Richard Wiles, executive director of the nonprofit Environmental Working Group, said yesterday that scientists don't know for certain whether a low-level, long-term exposure to this kind of combination of chemicals could cause problems. He said his group recommends that customers buy carbon filters for their tap water.

"Really, no one knows what the effect of drinking this chemical cocktail in your tap water over your lifetime is," Wiles said. "It's a legitimate health concern."