Toxins Contaminate U.S. Water Supply, Study Says : Health: At least 100 million Americans face ‘unnecessary risk,’ environmental group warns. Water companies insist report is inaccurate.

Arsenic, radon or byproducts of chlorination, each considered highly toxic, contaminate the drinking and bathing water of at least 100 million Americans, a major environmental group said Wednesday.

In a study based on data reported by more than 100 water utilities across the country, the Natural Resources Defense Council said that the water poses risks not only to those who drink it but also to those who inhale unnoticed fumes.

“Every American has a right to take a shower without hurting themselves,” said Erik Olson, a lawyer with the group that assembled the data. “We are not saying that people should panic, that people should stop drinking their water, that they should stop showering. We are saying there is an unnecessary risk.”

The findings were challenged by the American Water Works Assn., which represents water companies. It called the report “inaccurate and a distortion of data.”

Radon and arsenic occur naturally in ground water and “people have been drinking it for centuries. The data do not show the levels people have been drinking for years cause harm,” said Al Warburton, the association’s legislative director.

Arsenic and radon have been proven to cause cancer, although the level at which they are dangerous has not been firmly established. The chlorination byproduct involved in the study, trihalomethane, is a suspected carcinogen and is also suspected of causing birth defects. Chlorine is used in water to kill microbial bacteria.

The report’s release coincides with growing attention being paid in Congress to the safety of the nation’s water supply as the House and Senate prepare legislation setting new standards for water quality. Environmental organizations are concerned that relaxed standards might weaken protection against contaminants.

At the same time, the House has passed appropriations legislation restricting the Environmental Protection Agency’s authority to enforce water standards, and the Senate has passed a measure raising the level of certain contaminants considered acceptable.

The new study builds on work that the Natural Resources Defense Council carried out two years ago, which found that 350,000 Americans used water in which the level of arsenic violated federal standards.

The new study found that a much larger number of Americans--at least 60 million--face a lower, but still worrisome, level of arsenic in their public water supplies and that additional Americans face risk from radon and trihalomethane.

The report is based on data requested by the environmental group and submitted by some of the nation’s largest water authorities and companies, serving more than one-third of the nation. It was analyzed by the Natural Resources Defense Council and two other environmental groups.

Among the Southern California cities responding to the groups’ request for information, the Los Angeles Department of Water and Power reported that tap water contained an average of 10 to 25 parts per billion of arsenic. The Long Beach Water Department reported that its water contained 0.5 parts per billion, the report says, and the Southern California Metropolitan Water District reported 2 to 3 parts per billion.

Olson said that a 1992 University of California study found that 50 parts per billion would produce a 1 in 50 chance of a person developing a fatal cancer during an average lifetime and that 25 parts per billion would produce a 1 in 100 chance of developing such cancer. An EPA science advisory board said that arsenic should be considered a health risk if it occurs at levels of 100 parts per billion, twice as high as the 50 parts-per-billion level established as an EPA standard.

None of the Southern California jurisdictions taking part in the survey reported levels of radon in water supplies above the point considered a health risk, and dangerous levels of trihalomethane have not been established, the Natural Resources Defense Council said.

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Carol M. Browner, administrator of the EPA, said in a written statement that the report “underscores the need to strengthen public health protections against contamination of our drinking water and demonstrates that the public has a right to know about what is in our tap water.”

Another EPA official, speaking on condition of anonymity, said that the report is important because it “points out there are still concerns about drinking water” despite years of efforts to clean it up.

But, the official said, trihalomethane poses a problem because it is a byproduct of the disinfecting process and the agency is “struggling to strike the right balance.”