[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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