He said applying the data to humans assumes that the rodents’ stomach eliminated the same fraction of chromium VI 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-contaminated water 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.
EPA spokeswoman Enesta Jones said Thursday that hexavalent chromium is among 20 compounds selected in 2008 for review by the agency's Office of Research and Development. When officials there analyze all scientific literature, including the new study, they then will decide whether to change the old toxicity levels used to set standards for water and soil cleanup, she said.
Cleanup of Hinkley's contaminated water—an underground plume that is two miles long and one mile wide—began in the late 1980s and is continuing, according to California Water Resources Control Board documents. The contamination is still spreading, so the state issued its latest cleanup order to PG&E in August.
Brockovich, now president of a consulting firm, has since fought other legal battles related to chromium and other pollutants.
This article originally ran at Environmental Health News, a news source published by Environmental Health Sciences, a nonprofit media company.