RESEARCH TRIANGLE PARK, N.C., May 17 -- Sixteen years after activist Erin Brockovich first suggested that hexavalent chromium in drinking water might be a health hazard, a federal scientific panel has agreed with her.
After a two-year animal study, the National Toxicology Program said there is "clear evidence of carcinogenic activity" if the chemical is consumed in drinking water.
In the study, rats developed cancers of the oral cavity and mice developed cancers of the lower intestine, according to Michelle Hooth, Ph.D., of the toxicology program, which is part of the National Institute of Environmental Health Sciences here.
But Dr. Hooth noted that the cancers developed after extremely high doses, and the lowest dose given to the animals was still about 10 times higher than the concentration found in groundwater in Hinkley, Calif., the town where hexavalent chromium (or chromium six) first entered the public consciousness.
Commenting on the report, Brockovich told a news service she is "relieved and pleased and sorry because there are a lot of people who have ingested chromium six."
She added the ruling "is no surprise to me. This is a chemical that there have been ongoing arguments about, and now a third party has concluded that it can cause cancer by ingestion."
Hexavalent chromium compounds, used in electroplating, leather tanning, and textile manufacturing, have been considered a carcinogen when inhaled since 1990.
Brockovich was instrumental in starting a lawsuit against Pacific Gas & Electric Company, alleging that the company's Hinkley Compressor Station had polluted the town's water.
The lawsuit, settled in 1996 for $333 million, was dramatized in the 2000 movie named after Brockovich.
In the current study, rats and mice were given drinking water, over a two-year period, containing various concentrations of sodium dichromate dihydrate, an inorganic compound containing hexavalent chromium.
The lowest dose was 14.3 mg/L of water, equivalent to 5 mg/L of chromium. By comparison, the concentration in Hinkley groundwater was 0.58 mg/L of chromium.
The highest dose was 516 mg/L of sodium dichromate dihydrate, and it was at that level that most of the cancers were seen in the rats, Dr. Hooth and colleagues reported.
Among the mice, Dr. Hooth said, there was more of a dose-response reaction, with more lesions as the concentration of chemical in the water increased.
In rats, there was no difference in survival between exposed and control animals, but among the 99 animals getting the highest dose of the chemical, there were 18 cancers of the oral mucosa or tongue. The rates were significantly different from controls at P=0.007 for males and P=0.002 for females.
In the mice, there was again no difference in survival, but among the 100 animals getting the highest dose, there were 42 neoplasms, either adenoma of carcinoma. The differences from controls were significant at P<0.001 for males and females.
Dr. Hooth said it's not clear why the lesions were in the rats' oral cavity, while the mice had them in the lower intestine.
In fact, she said in an interview, "it was a surprise" to see the mice developing lower intestine cancers.
"We had thought that in the stomach, (the chromium) would be reduced from the hexavalent to the trivalent form, which is thought to be non-toxic," she said.
At higher doses, all the animals lost weight, compared to controls, but the researchers said that was at least partly the result of the animals finding the water unpalatable and drinking less.
Dr. Hooth said the next step is for the report to be approved by the full board of the National Toxicology Program. Once that's done, she said, it will be available for federal or state agencies to use in setting new regulations if they see fit.