2 Mice and Scientific Unknowns at Heart of Chromium Debate
For their entire lives in a German laboratory, 101 lab mice lapped up water containing extraordinary amounts of a metallic compound.
It was 1968, and scientists were trying to figure out whether chromium--widely used in industrial paints and plating materials--was dangerous in drinking water. Two of the mice developed stomach tumors so big that the mounds protruded from their bellies. All the others remained healthy.
The scientists concluded that the tumors were insignificant--perhaps just random chance--and that the cancer connection was equivocal.
Yet more than 30 years later, the fate of those two mice is the prime evidence that has been used by state health officials to recommend a stringent goal for chromium in drinking water. If enforced, that recommendation could shut down hundreds of wells across the Los Angeles area, especially in the San Fernando Valley, at a cost of tens of millions of dollars.
George Alexeeff, chief scientist at the state’s Office of Environmental Health Hazard Assessment, said the state goal may be “over-erring on the side of public health.” But that, he said, is exactly what public health officials must do--legally and morally--in the face of scientific uncertainty.
“The spirit of the law is when there’s a controversy, we’re to err on the side of being health protective,” he said.
Others disagree. The federal Environmental Protection Agency has dismissed the German study. And one of the world’s leading chromium experts, Max Costa of New York University, called it “totally stupid and scary” for California to calculate its health goal based on the fate of two mice.
Costa suspects that water containing even small amounts of chromium, particularly the most hazardous form, chromium 6, may be dangerous to people who are genetically susceptible to cancer. But he said the mouse study is so problematic that calculations derived from it are no more credible than pulling a number out of a hat.
To scientists, chromium 6, also known as hexavalent chromium, is an enigma. It alters DNA. It mutates cells. And it is among only a handful of chemicals proved to cause cancer in human beings.
But the danger, at least so far, has been proved only when chromium 6 particles are inhaled. There are no published studies that have found a significant cancer increase from drinking it, even in lab animals consuming extremely high concentrations. Published studies--one of people in China and several involving lab animals--have found no cancer link.
The EPA remains unconvinced that chromium 6 is carcinogenic in water. The proposed California health goal is 40 times more stringent than the EPA’s national standard.
The debate over chromium illustrates a problem faced by government agencies responsible for ensuring the safety of drinking water. Under law, federal and state officials are required to set standards for water pollutants, even when the scientific data are scarce, outdated or questionable.
“Science can’t give you the number you need, so the state has to make a policy decision. It’s not a scientific issue because the science is too uncertain,” said John Froines, a UCLA toxicologist who heads the state’s advisory board for evaluating toxicity of pollutants.
Given the ambiguities of the science, two prominent chromium experts, Costa and Silvio De Flora, a toxicologist at the University of Genoa in Italy, sharply disagree about how cautious public officials should be.
De Flora said chromium is carcinogenic, “but only in the respiratory tract . . . and only after exposures at very high doses, which are only encountered in three occupational settings” in the chrome production and metal-plating industries.
That position is backed by an international panel of experts, who found no link between human cancer and chromium in water.
“For cancers other than of the lung and sinonasal cavity, no consistent pattern of cancer risk has been shown among workers exposed to chromium compounds,” according to the 1990 report of the International Agency for Research on Cancer.
Some recent studies have detected an excess of stomach cancers and leukemia among workers in chromium production and plating industries. Those cancers would probably come from swallowing chromium particles, not breathing them, researchers say.
De Flora said he is convinced that “there is no possibility for oral chromium to induce cancer.”
The reason chromium 6 could be more toxic when inhaled than when swallowed is because stomach acids can convert a large amount of the compound into a form of chromium that cannot cross into cells.
But Costa, who heads NYU’s department of environmental medicine, said the protection offered by stomach acids is not absolute. Some people’s stomachs do not convert chromium well and may be vulnerable, he said.
Transported by Bloodstream
Once it enters the bloodstream, chromium 6 is readily transported into cells and can endanger tissues and organs throughout the body, Costa said.
“Your blood brings it into every cell in your body. It goes everywhere, and anyplace you put chromium 6 you get cancer,” he said.
It is likely, he said, that no cancers have been found in rats and mice only because the animals are poor models for humans. A substance that is so dangerous in the air is likely to be harmful in the water too, he said.
“We know chromium 6 is a carcinogen. So given that scientific information, why do we want to let people drink it?” Costa said.
Chromium 6 has been especially controversial because of a well-publicized case in Hinkley--a small town in the San Bernardino County desert--dramatized this year in the movie “Erin Brockovich.” Water there contained levels of chromium 6 that were thousands of times higher than those found in Los Angeles-area wells.
Residents of the town won a $333-million settlement from Pacific Gas & Electric in a lawsuit alleging that chromium 6 caused cancers and other serious diseases. But whether the illnesses were caused by drinking the compound or inhaling it was not determined.
Because the San Fernando Valley was a center of aerospace manufacturing, many parts of its aquifer contain measurable levels of chromium, including chromium 6. Shutting down wells there containing the chemical could cost an estimated $50 million in replacement water, officials estimate. The cities of Los Angeles, Burbank and Glendale have teamed together to try to develop technology to remove chromium from water.
State officials are required by the 1996 California Safe Drinking Water Act to set standards for 75 pollutants, including chromium.
The environmental hazards office must first recommend a public health goal for each pollutant. Then the Department of Health Services considers that goal when setting a maximum standard that water agencies must meet. The standard in many cases is more lenient than the goal because economic factors are considered.
The public health goal is a strictly mathematical computation, based on how much of a chemical would potentially cause one cancer among every million people exposed for a lifetime.
In most cases, as with chromium, the risk is calculated by extrapolating from very high concentrations fed to animals to the much lower concentrations to which people are exposed.
Relevance of Study Disputed
Based on the dose fed to the two German mice, the state’s proposed goal is 2.5 parts per billion of total chromium. At that level, state officials estimate that only 0.2 ppb would be chromium 6. The health agency has not yet decided whether to turn the goal into a standard. Until it does, the existing standard, 50 ppb of total chromium, is the only enforceable limit. Some wells being used for drinking water in the Lancaster area have been found to have levels of chromium 6 as high as 17.6 ppb.
Many scientists say the mouse study is irrelevant to humans, and they question whether the state should have used it.
The concentrations of chromium 6 were so high (500,000 ppb) that the mice were reluctant to drink it. Their water had almost 30,000 times higher concentrations than the wells in Lancaster. That amount of chromium is so caustic that irritation alone could have caused the mouse tumors.
Also, the 2% of mice that developed tumors is not considered statistically significant, and the cancers were found in their forestomachs, an organ that humans do not have.
Given those limitations, the EPA dismissed the study when setting a national standard and instead used another 1968 study, which showed no cancer in rats given water containing 25,000 ppb of chromium 6.
Alexeeff defends his agency’s recommendation, saying that there are several reasons in addition to the mouse study to be cautious with chromium 6: It is a potent and well-proven cause of lung cancer and there are indications of stomach cancers among chromium plant workers.
California health officials criticize the EPA as being too slow and too lenient in setting drinking water standards. EPA officials, however, say their chromium standard has a large margin of safety and they have no plans to change it.
Several toxicologists said concentrations found so far around Los Angeles are fairly low, so they should not pose much danger. But because of the uncertainties, they also urge public agencies to do whatever possible to get chromium 6 out of drinking water.
“I don’t think the numbers [found in Los Angeles-area wells] are very high, but given the potency of chromium, you can’t dismiss it either,” Froines said. “Chromium 6 is a bad compound, and there is enough evidence that you shouldn’t ignore it.”
(BEGIN TEXT OF INFOBOX / INFOGRAPHIC)
Chromium Concerns
Citing cancer concerns, the state Office of Environmental Health Hazard Assessment has recommended a stringent goal for the maximum level of chromium allowed in drinking water. The recommendation is controversial because scientific data are uncertain.
Concentration in water
Federal standard: 100 ppb total chromium
Current state standard: 50 ppb total chromium
Highest reported level in L.A. County wells now in use: Up to 17.6 ppb chromium 6
Proposed state public health goal: 2.5 ppb total chromium, with 0.2 ppb chromium 6
How to Protect Your Family
Whether small amounts of chromium 6 in water supplies create a risk at all is a hotly debated topic. But experts offer this advice to those who are concerned:
Only people who have cancer in their families should worry about exposure to chromium, and because vitamin C neutralizes chromium, they can minimize their risks by taking a vitamin with their drinking water.
