Misconceptions About Environmental Pollution, Pesticides and the Causes of Cancer

Studies | Environment

No. 214
Sunday, March 01, 1998
by Bruce N. Ames and Lois Swirsky Gold


Misconception #5: Human Exposures to Carcinogens and Other Potential Hazards Are Nearly All Due to Synthetic Chemicals

"The amounts of synthetic pesticide residues in plant foods are insignificant compared to the amount of natural pesticides produced by plants themselves."

On the contrary, 99.9 percent of the chemicals humans ingest are natural. The amounts of synthetic pesticide residues in plant foods are insignificant compared to the amount of natural pesticides produced by plants themselves.48 Of all dietary pesticides that humans eat, 99.99 percent are natural: they are chemicals produced by plants to defend themselves against fungi, insects, and other animal predators.49 Each plant produces a different array of such chemicals.

  • On average Americans ingest roughly 5,000 to 10,000 different natural pesticides and their breakdown products.
  • Americans eat about 1,500 mg of natural pesticides per person per day, which is about 10,000 times more than they consume of synthetic pesticide residues.

Even though only a small proportion of natural pesticides have been tested for carcinogenicity, 35 of the 63 tested are rodent carcinogens. Naturally occurring pesticides that are rodent carcinogens are ubiquitous in fruits, vegetables, herbs, and spices.50 [See Appendix Table II.]

"In a single cup of coffee the natural chemicals that are known rodent carcinogens are about equal in weight to a year's worth of synthetic pesticide residues."

Cooking foods produces about 2,000 mg per person per day of burnt material that contains many rodent carcinogens and many mutagens. By contrast, the residues of 200 synthetic chemicals measured by FDA, including the synthetic pesticides thought to be of greatest importance, average only about 0.09 mg per person per day.51 In a single cup of coffee the natural chemicals that are known rodent carcinogens are about equal in weight to a year's worth of synthetic pesticide residues that are rodent carcinogens, even though only 3 percent of the natural chemicals in roasted coffee have been adequately tested for carcinogenicity.52 [See Appendix Table III.] This does not mean that coffee or natural pesticides are dangerous, but rather that assumptions about high dose animal cancer tests for assessing human risk at low doses need reexamination. No diet can be free of natural chemicals that are rodent carcinogens.53


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