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Table Talk : Opinion Breaker : Bruce Ames: Standing By His Scientific Guns

August 11, 1994|CHARLES PERRY | TIMES STAFF WRITER

"Would you like a coffee?" asks Bruce Ames sociably. It might seem an odd offer. Ames is famous for having pointed out that a cup of coffee contains 10 milligrams of natural carcinogens.

As a matter of fact, Ames, who is 65, likes coffee. He and his Italian wife collect old espresso machines, and he brews a respectable cup. Besides, Ames never meant to scare people away from coffee. He was making a point about pesticides: Ten milligrams is how much artificial pesticide residue the average person ends up ingesting in a year. In other words, eating non-organic produce for a year is no more dangerous than drinking one cup of coffee. And what's the harm in that?

Ames' scientific credentials are imposing: chief of the microbial genetics section at the National Institutes of Health, chairman of the biochemistry department at University of California, Berkeley, member of the National Academy of Sciences. He has published 300 science papers, won numerous scientific awards and served on the board of directors of the National Cancer Institute.

At one time, he was a well-known critic of pesticides and synthetic food additives such as saccharin. "There is no question that society is going to pay for all the pesticides that have been used in the past," he told the New York Times ominously in 1977, "through increases in birth defects and cancer, but no one knows exactly what the price will be and when it will be paid."

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But about 15 years ago he started casting doubt on the idea that pesticides pose a major health risk. Today he'd go further and suggest that panic about the dangers of technology leads to policies that are not just inappropriate but downright dangerous to our health.

He sits in his office in Berkeley, surrounded by ceiling-high cases full of books and periodicals, and tells how his ideas developed, beginning the tale in the mid-1960s, when he was still at the National Institutes of Health, years before he became either an opponent or an advocate of pesticides.

"I was always sort of half in genetics and half in biochemistry," he says. "We were mutating bacteria to see how (genetic) regulatory pathways worked. I was interested in how genes got turned on and turned off.

"And then at one point, as a sort of side project, I started wondering about all the new chemicals coming into the environment. I was reading too many labels on potato chip packages," he says, chuckling. "I thought if some of these chemicals were mutagens (agents that change genes), that wouldn't be good.

"In those days, people didn't know what was causing cancer. There was an old theory that chemicals that caused cancer were mutagens--they were working by mutating the DNA. But a lot of carcinogens turned out not to be mutagens, and people said no, carcinogens are working in some mysterious way, but not as mutagens.

"Now, being a geneticist, all my intuition said mutagens had to be carcinogens. Cancer is when you have a cell that is different in some way, and the way you get that is by mutating it. Then in the cancer field a few people started showing that, say, benzopyrene, which is a very un reactive compound, isn't the real carcinogen. It's metabolized in the body into other chemicals, and some of those are reactive."

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Ames had developed a simple test (see box) that for many purposes replaced the older way of finding out whether a chemical might be carcinogenic. Before Ames, the only way to test for carcinogenicity was to try a chemical on animals, mostly rats or mice, for several years to see whether any of them developed cancer. Typically, the amount of the chemical given would be the Maximum Tolerated Dose (MTD), which is just less than the amount that would kill them outright by poisoning. Since virtually all chemicals are poisonous at very high doses, Ames and many other scientists believe that MTD tests do not show that a chemical is carcinogenic at low doses, only that cells may become cancerous under extreme stress.

Ames also stresses that MTD levels bear no relationship to the amount of a chemical a person encounters in the real world. However, MTD tests were mandated by the so-called Delaney Clause, an addition to the 1958 Federal Food, Drug and Cosmetic Act, which makes it illegal for processed foods to contain any detectable amount of a chemical that has ever been found to cause cancer, no matter how high a dose it took. Many authorities believe the Delaney Clause imposes an unrealistic standard of safety; last year Carol Browner, administrator of the Environmental Protection Agency, spoke of replacing it with a "negligible risk" standard.

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