WASHINGTON – An environmental group that analyzed the drinking water in 35 cities found that most contained hexavalent chromium, a probable carcinogen that was made famous by the film “Erin Brockovich.”

The study, which will be released Monday by the Environmental Working Group, is the first nationwide analysis of hexavalent chromium in drinking water to be made public.

It comes as the Environmental Protection Agency is considering setting a limit for hexavalent chromium in tap water. The agency is reviewing the chemical after the National Toxicology Program, part of the National Institutes of Health, deemed it a “probable carcinogen” in 2008.

The federal government restricts the amount of “total chromium” in drinking water and requires water utilities to test for it, but that includes both trivalent chromium, a mineral that humans need to metabolize glucose, and hexavalent chromium, the metal that has caused cancer in laboratory animals.

Last year, California took the first step in limiting the amount of hexavalent chromium in drinking water by proposing a “public health goal” for safe levels of 0.06 parts per billion.

Hexavalent chromium was a commonly used industrial chemical until the early 1990s. The chemical can also leach into groundwater from natural ores.

The new study found hexavalent chromium in the tap water of 31 out of 35 cities sampled.

The highest levels were in Norman, Okla., where the water contained more than 200 times the California goal.