The potential cost to water suppliers is unknown. The new recommendation ranks among the lowest health goals among nearly 90 toxic water pollutants regulated in the state.

Chromium 6 is found in ground water in large urban areas as well as rural areas. Used in metal plating, stainless steel production and other manufacturing, it has been detected in 30% of drinking water sources in California, according to state officials.

The Environmental Working Group compiled data showing that 519 water systems in California serving 33.4 million people contain chromium 6.

No other state tests water for the substance, Sharp said.

“We don’t even know how big of a problem it is nationally,” she said.

Scientists have known for two decades that people can contract lung cancer when inhaling it. But until recently, the science was uncertain about whether it causes cancer when swallowed.

Other goals have been set, then rescinded over the past decade. In 1999, after the Hinkley case, California set a goal of 2.5 ppb based on a 1968 study that found stomach tumors in animals that drank the substance. However, the U.S. EPA rejected that study and concluded there was no evidence chromium 6 was carcinogenic in water. California’s scientific advisors agreed, so the state rescinded its goal in 2001 and reverted to the old 50 ppb standard, which was based on the risks of skin irritation, not cancer.

A study in China found high rates of stomach cancers in people whose water was contaminated with so much chromium from a smelter that it had turned yellow. That study, however, was controversial because industry consultants intervened and republished the findings, making the science debatable.

The California environmental health office then asked federal scientists to resolve the quandary. Last year, the National Toxicology Program concluded that the chromium compound caused intestinal cancers, which are relatively rare in animals, as well as mouth cancers, and that it infiltrated the cells of many organs.

EPA officials said earlier this year that they plan to release results of their evaluation of the national standard this fall. The agency is required by federal law to review water standards every six years.

This article originally ran at Environmental Health News, a news source published by Environmental Health Sciences, a nonprofit media company.

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