by Bruce Ames
It is popular these days to espouse an apocalyptic vision of the future of our planet. Pollution and pesticides are being blamed for cancer, yet these and many other environmental scares are based on weak or bad science. Many of these fears are based on misconceptions.
One misconception is that high-dose animal cancer test tell us the significant risks for humans. A dividing cell is much more at risk to be mutated to a cancer cell than is a non-dividing, quiescent cell. Toxicity at or near the maximum tolerated dose often induces cell division. Below a certain dose, no such effect is observed. Therefore, it can be the high dose itself, rather than the chemical per se that is the risk factor for cancer. Very low levels of chemicals, to which humans are exposed through water pollution or synthetic pesticide residues, are likely to pose no or minimal cancer risks.
A second misconception is that human exposure to toxins are nearly all to synthetic chemicals. On the contrary, of all dietary pesticides, 99.99% are natural: They are toxins produced by plants. Americans eat an estimated 1,500 mg of natural pesticide/person/day. By contrast, the FDA found that residues of 200 synthetic chemicals average only about 0.09 mg/person/day.
The public has been led to believe synthetic toxins pose greater hazards than natural toxins. On the contrary, the proportion of natural chemicals that is carcinogenic when tested in both rats and mice is the same as for synthetic chemicals.
Another misconception is that the toxicology of man-made chemicals is different from that of natural chemicals. Humans have many general, natural defenses that buffer us against normal exposures to toxins, both natural and synthetic. DDT is often viewed as the typically dangerous synthetic pesticide. However, it saved millions of lives in the tropics and made obsolete the pesticide lead arsenate, which is even more persistent and toxic, although all natural. While DDT was unusual with respect to bioconcentration, natural pesticides also biocon-centrate if they are fat soluble.
There are trade-offs involved in eliminating pesticides. In selecting for natural pest resistance, plant breeders are selecting plants higher in natural toxins.
Synthetic pesticides have markedly lowered the cost of plant foods, making them more available to consumers. Huge expenditures of money and effort on tiny hypothetical risks do not improve public health. Rather, they divert resources from real human health hazards and hurt the economy.
American life expectancy increases every year, as does life expectancy around the world, in good part due to modern agriculture making healthy diets cheaper.
This article was written by Bruce Ames, a professor of biochemistry and molecular biology at the University of California, Berkeley. Ames is a member of the National Academy of Sciences. His work on detecting mutagens has been widely used by agencies including the FDA in its pesticide registration process.
Reprint permission given by AgAir Update, P.O. Box 850, Perry, GA 31069 - an international agricultural aviation publication.
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