The carcinogen often referred to as the "Erin Brockovich chemical" is present in about two-thirds of the drinking water across the country, according to water testing data from the Environmental Protection Agency.
Low levels of chromium-6 have been found in drinking water in New England, including in Vermont. The federal government recognizes that even at low levels it can be harmful, but the EPA has not yet set an enforceable drinking water standard for states to follow. One challenge to treating drinking water in New England is it's hard to tell where the chromium-6 is coming from.
Relative to some hotspots in California, Arizona and Oklahoma, the levels of chromium-6 found in New England drinking water are quite low. Most were under 1 part per billion.
Still, even those low levels exceed than the public health goal set by the state of California, which is 0.02 parts per billion.
"California did a very reasonable assessment of the carcinogenicity of chrome-6, and I agree for the most part with what their conclusions are regarding the risk of chrome-6," says Sarah Vose, the state toxicologist of Vermont. "There's no doubt it’s a public health concern."
However, Vose points out that while chromium-6 levels in parts of New England are above California's health goal, these levels are below that state's enforceable limit — so even these levels would go untreated in California, the only state with a legally enforceable limit in drinking water.
Chromium-6 is a known human carcinogen. Most chromium-6 in the environment comes from industrial sources. It's used for chrome plating, leather tanning and wood preserving, and is also found in the ash from coal-burning power plants.
Another form of the chemical, chromium 3, is naturally occurring in the environment — and it's a nutrient that our bodies need. But chrome 3 can convert to chromium-6 under different conditions.
"We've been working on understanding the toxicity of chromium for a number of years, and next year, 2017, we'll be publishing a draft health assessment for chromium," says Peter Grevatt, the director of EPA's office of Ground Water and Drinking Water.
In New England, because the levels of chromium-6 are so low — and the source of the chemical isn't clear — officials aren't yet sure how to treat the contamination.
"We kind of need to know what the original source of this is, to deal with it. If it’s from atmospheric deposition or its naturally occurring in the water itself, you’d be thinking treatment plant issues, how can we properly treat there," says Ellen Parr Doerring, the deputy director for the Drinking Water and Groundwater Protection Division in Vermont.
Or she says, it can be even trickier: There's some evidence that certain chemicals used to make drinking water safer could actually cause this the nutrient chromium 3 to convert to chromium-6. Or it could be leaching from distribution pipes.
"Then you might be looking at another way of dealing with issue, and right now at these low levels, it’s really hard to figure out, what is the issue, why is that happening," says Parr Doerring.
Parr Doerring says Vermont and the other New England states first saw the data on chromium-6 in drinking water when the EPA shared it about a year ago; and state officials did have conversations about the carcinogen.
"But we hadn't come up with New England wide strategy," says Parr Doerring.
And even if the state knew the source of contamination, it's not clear if it's technically feasible to treat such low levels.
The nonprofit Environmental Working Group has been working to draw attention to the issue across the country, and recently published a comprehensive report using the EPA data. David Andrews is a chemist with the group, and he says the uncertainty around what to do points to a bigger problem.
"It raises important questions about our national drinking water infrastructure, and the ability of our federal government to essentially keep informed and be able to update drinking waster standards as science evolves," Andrews says.
The EPA says it will issue an assessment of the toxicity of chromium-6 in 2017, and then after a period of public comment, determine if an enforceable drinking water standard should be set.
This report comes from the New England News Collaborative: Eight public media companies coming together to tell the story of a changing region, with support from the Corporation for Public Broadcasting.