Mother Nature's Pesticides
By John Tierney
NEW YORK TIMES BLOG
Tags: DDT, pesticides, Rachel Carson
When I posted on research by Bruce Ames and Lois Swirsky Gold showing that humans ingest a lot more natural pesticides than synthetic pesticides, I expected a sequel to the earlier denunciations from Rachel Carson's admirers. (To answer their most frequent question: No, I am not accepting bribes from chemical companies.)
But I was pleasantly surprised by the latest round of comments. Yes, some readers did object, and some echoed Ms. Carson's argument that the synthetic pesticides are more of a menace. But the debate was dominated by readers like Andrew, Dennis Mangan, Doc Individ and Btavshanjian. They concentrated on the chemistry of toxins instead of making generalizations about nature or corporations. And when you make a dispassionate comparison of natural versus synthetic pesticides, Mother Nature doesn't come out so well.
Rachel Carson was naive to assume there were "few" natural carcinogens, and she was also naive to assume that evolution had made us "accustomed" to these chemicals. Dr. Ames and Dr. Gold explain why we never had a chance to get accustomed:
"Humans have not had time to evolve a "toxic harmony" with all their dietary plants. The human diet has changed markedly in the last few thousand years. Indeed, very few of the plants that humans eat today, e.g., coffee, cocoa, tea, potatoes, tomatoes, corn, avocados, mangoes, olive and kiwi fruit, would have been present in a hunter-gatherer's diet. Natural selection works far too slowly for humans to have evolved specific resistance to the food toxins in these newly introduced plants."
Of course, our ancestors did develop defenses against toxins. But why assume these defenses work only against natural toxins? Dr. Ames and Dr. Gold don't buy that assumption:
"Humans have many natural defenses that buffer against normal exposures to toxins and these are mostly general, rather than tailored for each specific chemical. Thus they work against both natural and synthetic chemicals. Examples of general defenses include the continous shedding of cells exposed to toxins. The surface layers of the mouth, esophagus, stomach, intestine, colon skin and lungs are discarded every few days; DNA repair enzymes, which repair DNA that was damaged from many different sources; and detoxification enzymes of the liver and other organs which generally target classes of chemicals rather than individual chemicals. It makes good evolutionary sense to conclude that human defenses are usually general, rather than specific for each chemical. The reason that predators of plants evolved general defenses is presumably to be prepared to counter a diverse and ever-changing array of plant toxins in an evolving world."
Dr. Ames and Dr. Gold have also addressed the objection that synthetic pesticides have peculiarly dangerous properties:
"DDT was unusual with respect to bioconcentration, and because of its chlorine substituents it takes longer to degrade in nature than most chemicals; however, these are properties of relatively few synthetic chemicals. In addition, many thousands of chlorinated chemicals are produced in nature. Natural pesticides also can bioconcentrate if they are fat-soluble. Potatoes, for example, contain solanine and chaconine, which are fat-soluble, neurotoxic, natural pesticides that can be detected in the blook of all potato eaters. High leels of these potato neurotoxins have been shown to cause birth defects in rodents, although they have not been tested for carcinogenicity."
To repeat, Dr. Ames and Dr. Gold are not suggesting that you stop eating potatoes or fear the plethora of natural pesticides in the produce department. The doses are generally too small to pose a risk. But if, as the scientists estimate, these natural pesticides are 10,000 times more plentiful in your diet than synthetic ones, why worry so much about the chemicals that don't come from Mother Nature?
tierneylab.blogs.nytimes.com |
