Decade of Research Reveals Cancer Danger in Town's Drinking Water
Continued from previous page
"Since they found tumors in the small intestine, that shows it was not eliminated in the stomach," Alexeeff said.
Cancer in the small intestine is "relatively rare" in animals, even those exposed to other chemicals, the scientists reported. In addition, chromium caused mouth cancers, and infiltrated the cells of many organs, including livers and pancreatic lymph nodes.
Mice and rats were exposed to four different doses, and they contracted cancer at lower levels than in the 1968 study, according to Michelle Hooth, a toxicologist at the National Institute of Environmental Health Sciences who was the study’s lead scientist.
That suggests California’s new goal could be as stringent as the rescinded 2.5 ppb one.
Chromium is widely used in metal plating, stainless steel production, wood preservation and textile manufacturing. It has been detected in 30% of drinking water sources in California, at levels mostly under the existing 50 ppb state standard, according to the state health department.
Some of the rats and mice developed malignant intestinal tumors when fed doses as low as 57,000 ppb -- 100 times higher than the Hinkley water levels -- for up to two years, Hooth said. The higher the dose, the more cancers found among the animals.
When setting a standard, scientists use high animal doses to extrapolate to a lower dose designed to protect people from a 70-year lifetime of exposure. Water standards are usually designed to keep the cancer risk to one case in every million or 100,000 people.
Gwiazda, who has served on EPA and California scientific advisory panels, said extrapolating the animal findings for humans creates uncertainty because the rodents had to be fed higher doses.
He said applying the data to humans assumes that the rodents’ stomach eliminated the same fraction of chromium 6 at high doses that the human stomach would at lower doses.
"This assumption is flawed in my view because the stomach has a very high reducing capacity," Gwiazda said.
As a result, such extrapolations could lead to an overly restrictive water standard, he said. "On the other hand," he added, "there is probably a subpopulation of sensitive individuals with diminished stomach reducing capacity due to illness." For those people, a standard based on the animal data "may not be protective enough," he said.
There also is human evidence that drinking hexavalent chromium can cause cancer. A study in China found high rates of stomach cancers in people whose water was contaminated with so much chromium from a smelter that it had turned yellow.
California state scientists will release their draft Public Health Goal for public comment "within the next couple of weeks," said Sam Delson, the Office of Environmental Health Hazard Assessment's deputy director of external and legislative affairs.
The new study, Alexeeff said, "is a large foundation of our results." The National Toxicology Program released some of its initial data last year, but the full report came out in December.
The number that Alexeeff's staff recommends will then be used by the state’s health department to formulate a maximum allowable amount for water supplies. The health department factors in the cost and technical feasibility when it sets that standard.
"We come up with a goal, and it’s up to the health department to propose a maximum contaminant level," Alexeeff said.
U.S. EPA officials also are evaluating the national 100 ppb standard and plan to release their results this fall. The agency is required by federal law to review water standards every six years. The EPA had adopted a more stringent chromium standard in 1977 but raised the allowable amount in 1991 in response to the lack of cancer evidence.