Decade of Research Reveals Cancer Danger in Town's Drinking Water

A controversial water contaminant made famous by Erin Brockovich and a small California desert town is carcinogenic.

That conclusion by federal scientists, culminating more than a decade of debate, is likely to trigger new, more stringent standards limiting the amount of hexavalent chromium allowable in water supplies.

It’s been known for about 20 years that people can contract lung cancer when inhaling hexavalent chromium, also known as Chromium 6. But until now, toxicologists have been uncertain whether it causes cancer when swallowed.

National Toxicology Program scientists reported that their two-year animal study "clearly demonstrates" that the compound is carcinogenic in drinking water. Mice and rats contracted malignant tumors in their small intestines and mouths when they drank water containing several different doses of hexavalent chromium.

"I think it’s resolved, as much as it can be resolved," said George Alexeeff, deputy director of scientific affairs at California’s Office of Environmental Health Hazard Assessment.

Based largely on the new cancer findings, California and U.S. Environmental Protection Agency officials are re-evaluating what concentration is safe in water supplies. Within a few weeks, California is expected to announce a proposal to set a new health guideline.

The Mojave Desert town of Hinkley, population of around 1,900, has the highest levels of hexavalent chromium reported in U.S. ground water. The compound seeped into water there from a Pacific Gas and Electric facility that used it to inhibit rust in cooling towers and discharged it into holding ponds in the 1950s and 1960s.

In 1996, PG&E paid a $333 million settlement to about 600 residents of Hinkley after Brockovich, a law clerk, investigated the contamination and found high rates of cancer and other diseases. The town's plight drew national attention in 2000 from a film based on Brockovich's legal crusade. The payment was the largest tort injury settlement in U.S. history.

The animal study does not prove that people in Hinkley contracted cancer from drinking the tainted water. But it does resolve the debate over whether the contaminant is capable of causing some types of cancer.

Roberto Gwiazda, an assistant researcher at University of California at Santa Cruz’s Department of Environmental Toxicology, called the new study a "milestone," saying it "settles the issue."

However, Gwiazda said, using the new research "to support a drinking water standard is a different matter" because extrapolating it to humans remains controversial.

Hinkley’s ground water contained concentrations as high as 580 parts per billion, more than 10 times California’s current drinking water standard of 50 ppb for total chromium compounds. The national standard is 100 ppb.

Because of the cancer uncertainty, California has had a tumultuous history of setting water standards to protect people from chromium.

In 1999, after the Hinkley case, California set a water guideline, called a Public Health Goal, of 2.5 ppb. It was based on a 1968 study in Germany that found stomach tumors in animals that drank the substance. However, the U.S. EPA rejected that study as flawed and determined there was no evidence it was carcinogenic in water. California’s scientific advisors agreed, so the state rescinded its goal in 2001 and reverted to the 50 ppb standard, which was adopted in 1977 and based on the risks of skin irritation, not cancer.

The debate focused on whether hexavalent chromium is neutralized in the stomach by gastric acids that turn it into Chromium 3, an essential nutrient.

California officials, seeking to resolve the controversy, asked the National Toxicology Program to conduct animal tests.