In a long-awaited move designed to protect people from cancer, California on Thursday proposed a new health goal for chromium 6 in drinking water that is thousands of times lower than the amount contaminating some water supplies.

The recommendation culminates a decade of debate among scientists trying to decide what concentration is safe to drink. The controversial water contaminant was made famous by Erin Brockovich and a small Mojave Desert town that won the largest tort injury settlement in U.S. history.

The proposal “is the first in the nation that identified a health-protective level of chromium 6 in drinking water,” said Joan Denton, director of the California Office of Environmental Health Hazard Assessment.

The office’s new recommendation, called a “public health goal,” is 0.06 parts per billion. The state’s current standard for total chromium compounds in drinking water is 50 ppb—about 800 times higher. The national standard is 100 ppb.

The health guideline is not enforceable at this point, but it will prompt a more stringent state regulation for water supplies throughout California. Under state law, that regulation must be as close to the public health goal as possible, taking into account what is technically and financially feasible for water suppliers.

The U.S. Environmental Protection Agency is reevaluating the national standard but has not yet issued a proposal.

Renee Sharp, director of the California office of the Environmental Working Group, an environmental health advocacy organization, said it is “definitely a good health guideline” that was “too long in coming.”

“We really want to see the state act very quickly to set a drinking water standard. It’s so clear that there are so many Californians being exposed,” she said, adding that “this is a significant public health issue that needs to be addressed not just in California, but nationally.”

California proposed the new goal because a recent federal study resolved a decade-long debate by concluding that chromium 6 can cause cancer when ingested.

The 0.06 ppb was calculated by determining the amount, based on the new animal data, that might cause no more than one cancer among every one million people exposed for a lifetime.

The small town of Hinkley in San Bernardino County has the highest levels of chromium 6, also known as hexavalent chromium, ever reported in U.S. water. Its ground water contained as much as 580 parts per billion--nearly 10,000 times higher than the new proposed goal.

Based on the state’s new recommendation, Hinkley residents who drank that level in water over their lifetime faced an extremely high cancer risk—an estimated one cancer for every 100 people exposed.

The compound seeped into the water from a Pacific Gas and Electric facility where it was used to coat cooling towers and discharged into holding ponds in the 1950s and 1960s.

PG&E paid a $333 million settlement to about 600 residents of Hinkley in 1996, after Brockovich, a law clerk, investigated the contamination and found high rates of cancer and other diseases. A 2000 film was based on Brockovich's legal crusade.

Cleanup of Hinkley's contaminated water--an underground plume that is two miles long and one mile wide--began in the late 1980s and is continuing.

Denton’s office will accept public comments on its proposal until Oct. 19. Then, another agency, the California Department of Public Health, will adopt a regulation setting a maximum allowable level for water supplies based on the health goal but also considering economic and technological complications.

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.