USGS: Chemicals Remain in Public Drinking Water After Treatment

Water from nine selected rivers used as sources for public water systems was analyzed for the study. The populations in communities served by these water treatment plants vary from 3,000 to over a million.

Testing sites include the White River in Indiana; Elm Fork Trinity River in Texas; Potomac River in Maryland; Neuse River in North Carolina; Chattahoochee River in Georgia; Running Gutter Brook in Massachusetts; Clackamas River in Oregon; Truckee River in Nevada; and Cache La Poudre in Colorado.

Scientists tested water samples for about 260 commonly used chemicals, including pesticides, solvents, gasoline hydrocarbons, personal care and household products, disinfection by-products, and manufacturing additives.

The Harry Nice Bridge crosses the Potomac River at Morgantown, Maryland. (Photo by Geoff Greene)

Low levels of about 130 of the chemicals were detected in streams and rivers before treatment in the source water at the public water facilities. Nearly two-thirds of those chemicals were also detected after treatment.

The most commonly detected chemicals in the source water were herbicides, disinfection by-products, and fragrances. Most of the chemicals found were at levels equivalent to one thimble of water in an Olympic-sized pool.

"Low level detection does not necessarily indicate a concern to human health, but rather indicates what types of chemicals we can expect to find in different areas of the country," said USGS lead scientist, Gregory Delzer.

"Recent scientific advances have given USGS scientists the analytical tools to detect a variety of contaminants in the environment at low concentrations; often 100 to 1,000 times lower than drinking-water standards and other human-health benchmarks," he explained.

Delzer said that chemicals included in this study serve as indicators of the possible presence of a larger number of commonly used chemicals in rivers, streams, and drinking water.

Many of these chemicals are among those often found in ambient waters of 186 rivers and streams sampled by USGS since the early 1990s, and are correlated with the presence of upstream wastewater sources or upstream agricultural and urban land use.

About 120 chemicals were not detected at all.

Measured concentrations of chemicals detected in both source water and treated water were generally less than 0.1 part per billion.

More than 75 percent of source water and treated water samples in this study contained five or more chemicals.

"The common occurrence of chemical mixtures means that the total combined toxicity may be greater than that of any single contaminant present," the USGS said in a statement accompanying the report.

The USGS report identifies the need for continued research because the additive or synergistic effects on human health of mixtures of man-made chemicals at low levels are not well understood.

"Most of the man-made chemicals assessed in the USGS study are unregulated in drinking water and not required to be monitored or removed," says Tom Jacobus, general manager of the Washington Aqueduct, which provides drinking water for one million people in the District of Columbia, Arlington County, Virginia, and the City of Falls Church, Virginia,

"These findings are not surprising and they will be important in helping regulators and assisting water utility managers arrive at decisions about future water treatment processes," Jacobus said.

This study did not look at pharmaceuticals or hormones nor did it examine the implications of the findings to ecosystems or aquatic health.

Although potential human-health effects and risk were not assessed in this study, the USGS said that adverse effects to human health are expected to be "negligible" based on comparisons of measured concentrations and available human-health benchmarks.

Click here for the full source-water quality assessment and listing of chemicals.

The USGS National Water-Quality Assessment Program is planning to complete as many as 21 additional surface-water assessments through 2013. A companion study is scheduled for release in 2009 that summarizes the occurrence of the same chemicals in high-production wells and the associated treated water in 13 states.

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