[Homestead] Natural pesticides versus artificial pesticides, in humans
Gene GeRue
genegerue at ruralize.com
Tue Jun 12 08:05:20 EDT 2007
Bev, and any other chemists on the list, what is your reaction to this?
June 12, 2007, 12:43 am
Mother Nature’s Pesticides
By John Tierney
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?
http://tierneylab.blogs.nytimes.com/2007/06/12/mother-natures-
pesticides/
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