Environmentalists Condemn Report : Biochemist at UC Ranks Hazardous Substances
The first effort to rank the relative potential hazard to humans from exposure to man-made and naturally occurring cancer-causing substances is reported in today’s Science magazine by Bruce N. Ames, a controversial biochemist at the University of California, Berkeley.
Ames concludes that low levels of pesticides and other man-made chemicals in food and water represent a much smaller cancer hazard than many naturally occurring chemicals.
His goal, Ames said, is “to put the possible hazards of man-made carcinogens in proper perspective. . . . It is important not to divert society’s attention away from the few really serious hazards, such as tobacco and saturated fat (for heart disease), by the pursuit of hundreds of minor or non-existent hazards.”
The report was roundly condemned by environmentalists, who have long considered Ames an apologist for industry. The paper is “really disturbing--a serious disservice to standard public health policy,” said Lawrie Mott of the Natural Resources Defense Council.
Other scientists were somewhat less critical, although still hesitant to accept Ames’ conclusions. “His approach is an oversimplification of the problem because we still don’t know how chemicals cause cancer,” said toxicologist James K. Selkirk of the National Institute of Environmental Health Sciences.
“Ames is saying that we cannot make risk assessments very accurately at extremely low doses (of potentially carcinogenic chemicals), and that is certainly true,” said Lawrence Garfinkel, director of cancer prevention for the American Cancer Society. “But on a regulatory basis, we have to let people know about potential carcinogens and take steps to protect them.”
Ames’ argument that “we should go after things with the highest risk first and not worry about those that have small risk is pretty sound,” said toxicologist Robert McGaughy of the U.S. Environmental Protection Agency. “That’s what we try to do at EPA, but it is very difficult to do scientifically, and there is a lot of room for disagreement.
“Ames has a point,” said Stanford environmental scientist Alice S. Whittemore, vice chair of the scientific panel that is advising Gov. George Deukmejian about toxic chemicals under the mandate from Proposition 65. “Our best knowledge indicates that many of these exposures are minor, and I would not want to be put in the position of arguing against him.”
Ames achieved fame about 15 years ago when he developed a simple test for identifying mutagens, chemicals that cause mutations. That test is now widely used, along with many others developed subsequently, for identifying potentially hazardous chemicals.
He has received the General Motors Cancer Research Foundation Prize, the most prestigious award in cancer research, as well as the Tyler Prize, which carries equal significance in environmental research.
Ames particularly provoked the ire of environmental activists when he wrote an anti-Proposition 65 argument that was included in state voter pamphlets last fall. After the election, Deukmejian named Ames as one of the 12 members of the advisory panel, a choice that was widely criticized by environmentalists.
The conclusions of Ames’s Science paper are not significantly different from arguments he has made in the past, but for the first time he has assigned numerical risks to individual chemicals.
The most important number he uses is called TD-50, which is the amount of any chemical that must be fed to rodents to produce tumors in half of them. For any chemical, he divides the average daily exposure of humans to the chemical by its TD-50 to produce a relative measure of risk, which he calls HERP for Human Exposure dose/Rat Potency.
HERP for one quart of ordinary tap water, for example, is 0.001. The similar value for the “worst” of the 32 wells in Silicon Valley ordered closed by EPA is 0.004, indicating that its relative hazard is four times as high.
In contrast, he said, HERP for a bottle of beer is 2.8, so its hazard is 2,800 times that of tap water. HERP for a glass of wine is 4.7.
“I’m not suggesting that people should be worried about drinking a couple of bottles of beer or a glass of wine,” Ames said in a telephone interview. “I don’t think the risk from those is very large. My point is that the risk from man-made chemicals in water is smaller still.”
Similarly, he said, the risks from pesticide residues in food are much smaller than is generally believed. “The total amount of pesticides we consume daily is about 150 micrograms,” he said, and only about a third of that is carcinogenic. “But you get 4,000 micrograms of carcinogens in one cup of coffee. It doesn’t mean a cup of coffee is dangerous. You just have to compare it to other things.”
Biochemist Beverly Paigen of the Oakland Children’s Hospital argued, however, that Ames has been potentially deceptive in his selection of chemicals for inclusion in the list and that he is misusing statistics. She noted, for example, that the two pesticides Ames ranked--DDT and EDB--are banned by the government and thus would not be expected to appear in food in significant quantities.
Paigen also argued that aflatoxin, a potent carcinogen produced by a mold that affects peanuts, seems to be active primarily in people who have had hepatitis and thus is not as great a risk to the general public as Ames suggests.
Mott also said Ames’ analysis overlooks other effects of the chemicals he studied. She agreed with Ames, for example, that wells contaminated with trichloroethylenes (TCEs) in Silicon Valley are very weak carcinogens but noted that they also produce severe effects on fetuses, the neurological system and the immune system.
“Until we know a lot more about the molecular biology and biochemistry of carcinogenesis,” Selkir said, “I would not wish to place any portion of the population at risk based on a mathematical manipulation.”
