Science and the Environment; B. Ames

Scientific advances and free markets can also lead to technologies that minimize pol lution for the lowest cost. A market for pollution rights is desirable-polluting shouldn't be free-and is much more effec tive than a bureaucratic monopoly. In my scenario for the future, I would like to see environmentalism based on scientific evi dence and directed at solving real problems rather than phantoms. An example of this problem is the public misconception that pollution is a significant contributorto cancer and that cancerrates are soaring. As life expectancy continues to increase in industrialized countries, cancer rates (unadjusted for age) also increase; Bruce Ames is Professor of Biochemistry and Molecular Biology at the University of Califor nia, Berkeley, where he is also the Director ofthe Environmental Health Sciences Center. however, the age-adjusted cancer death rate in the United States for all cancers com bined (excluding lung cancer from smoking) has been steady or decreasing since 1950.

Decreasing since 1950 are primarily stom ach, cervical, uterine, and rectal cancers. Increasing are primarily lung cancer (which is due to smoking, as are 30 percent of all U.S. cancer deaths), melanoma (possibly due to sunburn), and non-Hodgkin's lym phoma. Cancer is fundamentally a degener ative disease of old age, although external factors can increase cancer rates (cigarette smoking in humans) or decrease them (eat ing more fruits and vegetables). A second misconception is that high-dose animal cancer tests tell us the significant cancer risks for humans. Approximately half of all chemicals-whether natural or synthetic-that have been tested in standard animal cancer tests have turned out to be carcinogenic. These standard tests of chem icals are conducted chronically, at near toxic doses-the maximum tolerated dose and evidence is accumulating that it may be the high dose itself, rather than the chemical perse thatis the riskfactorfor cancer.(This is because high doses can cause chronic wounding of tissues or other effects that lead to chronic cell division, which is a major risk factor for cancer.) At the very low levels of chemicals to which humans are exposed through water pollution or synthetic pesti cide residues, such increased cell division 343 344 THE FREEMAN. SEPTEMBER 1993 does not occur. Thus, they are likely to pose no or minimal cancer risks.

The third misconception is that human exposures to carcinogens and other toxins are nearly all due to synthetic chemicals. On the contrary, the amount of synthetic pes ticide residues in plant foods are insignifi cant compared to the amount of natural pesticides produced by plants themselves. Of all dietary pesticides, 99.99 p~rcent are natural: They are toxins produced by plants to defend themselves against fungi and an imal predators. Because each plant pro duces a different array of toxins, we esti mate that on average Americans ingest roughly 5,000 to 10,000 different natural pesticides and their breakdown products. Americans eat an estimated 1,500 milli grams of natural pesticides per person per day, which is about 10,000times more than they consume of synthetic pesticide resi dues. By contrast, the FDA found the res idues of 200 synthetic chemicals, including the synthetic pesticides thought to be of greatest importance, average only about 0.09 milligram per person per day.

The fourth misconception is that syn thetic toxins pose greater carcinogenic haz ards 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 chemi cals-roughly half. All chemicals are toxic at some dose, and 99.99 percent of the chemicals we ingest are natural. The fifth misconception is that the toxi cology of man-made chemicals is different from that of natural chemicals. Humans have many general natural defenses that make us well buffered against normal expo sures to toxins, both natural and synthetic. DDT is often viewed as the typically dan gerous 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 un usual with respect to bioconcentration, natural pesticides also bioconcentrate if they are fat soluble. Potatoes, for example, nat urally contain fat soluble neurotoxins de tectable in the bloodstream of all potato eaters. High levels of these neurotoxins have been shown to cause birth defects in rodents.

The sixth misconception is that correla tion implies causation. The number of storks in Germany has been decreasing for de cades. At the same time, the German birth rate also has been decreasing. Aha! Solid evidence that storks bring babies! Cancer clusters in small areas are expected to occur by chance alone, and there is no persuasive evidence from either epidemiology or toxi cology that pollution is a significant cause of cancer for the general population. There are tradeoffs involved in eliminat ing pesticides. Plants need chemical defens es-either natural or synthetic-in order to survive pest attack. One consequence of disproportionate concern about synthetic pesticide residues is that some plant breed ers are currently developing plants to be more insect-resistant and inadvertently are selecting plants higher in natural toxins. A major grower recently introduced a new variety of highly insect-resistant celery into commerce. The pest-resistant celery con tains 6,200 parts per billion (ppb) of carcin ogenic (and mutagenic) psoralens instead of the 800 ppb normally present in celery. The celery is still on the market.

Synthetic pesticides have markedly low ered the cost of plant foods, thus making them more available to consumers. Eating more fruits and vegetables is thought to be the best way to lower risks from cancer and heart disease, other than giving up smoking; our vitamins, anti-oxidants, and fiber come from plants and are important anti-carcino gens. Thus, eliminating essential pesticides is likely to increase cancer rates. Huge expenditure of money and effort on tiny hypothetical risks does not improve public health. Rather, it diverts our resources from real human health hazards, and it hurts the economy. D THEFREEMAN IDEASON UBERTY OVERPOPULATION: THE PERENNIAL MYTH by David Osterfeld "What mostfrequently meets our view (and occasions complaint) is our teeming popu lation. Our numbers are burdensome to the world, which can hardly support us . ... In very deed, pestilence, and famine, and wars, and earthquakes have to be regarded as a remedy for nations, as the means of pruning the luxuriance ofthe human race."