The California Environmental Protection Agency (EPA) of the United States has issued the nation's first public health goal for hexavalent chromium, the cancer- causing heavy metal in drinking water, according to local media reports on Saturday.

The new state goal was set at 0.02 part per billion (ppb), the level of the element that does not pose a significant health risk in drinking water.

That means for every million people who drink tap water with that level of hexavalent chromium every day for 70 years, there would likely be one additional case of cancer attributable to exposure to the metal, The Los Angeles Times quoted state officials as saying.

The goal isn't an enforceable standard, but "will be an important tool that the Department of Public Health will use" to develop one, said George Alexeeff, acting director of the EPA's Office of Environmental Health Hazard Assessment.

Other state environmental officials offered reassurances that the new goal did not indicate any increased threats from hexavalent chromium, also known as chromium 6.

California environmental officials have detected hexavalent chromium in the drinking water of an estimated 13 million people in 52 of the state's 58 counties, including Los Angeles.

At least 74 million Americans in 42 states drink chromium- polluted tap water, much of it probably tainted with hexavalent chromium, according to studies by the nonprofit Oakland-based Environmental Working Group. They also found chromium 6 in tap water from 31 of 35 cities tested last year, with some of the highest levels in Riverside (1.69 ppb) and San Jose (1.34 ppb).

Chromium 6 occurs naturally in some drinking water, and many people don't even know they are drinking it. More often, it enters the water supply from industrial contamination, leaching from industrial and disposal sites.

Young children could be more susceptible to health risks from exposure to chromium 6, scientific studies show.

Mice and rats that drank water containing high levels of the element developed gastrointestinal tumors, according to a 2007 study by the National Toxicology Program.

The national drinking water limit for chromium is 100 ppb, but water system monitors are not required to distinguish what percentage of that is chromium 6 versus other less harmful ions such as chromium 3.