Dietary pesticides (99.99% all natural)

Plants are not just food for animals… The world is not green. It is colored lectin, tannin, cyanide, aflatoxin, and canavanine [Janzen (16)].

A false claim keeps crossing my desk: that organic foods are safer; and especially safer due to the prohibition of synthetic pesticides. This is false. In fact the motivation for development of many of the synthetic pesticides in use today is to reduce toxicity for both consumers and agricultural workers. This effort has been successful, but due to the vested interests in the “organic” marketing designation the prohibition against synthetic pesticides prevails.

John R. Block was U.S. secretary of agriculture from 1981 to 1986, so he is a good source for a concise summary of what “organic” really means:

The Organic Seal does not and cannot signify any health or safety criteria whatsoever. It merely certifies that products were produced using less modern inputs.

“Let me be clear about one thing,” said USDA Secretary Dan Glickman when organic certification was being considered. “The organic label is a marketing tool. It is not a statement about food safety. Nor is ‘organic’ a value judgment about nutrition or quality.”

Yet USDA’s own research shows consumers buy higher priced organic products because they mistakenly believe them safer and more nutritious.

The science is clear on this point: As numerous studies, USDA monitoring, and a massive “meta-analysis” recently conducted at Stanford University confirm, organic foods are no more nutritious, nor do they carry any fewer health risks, than conventional foods. In fact, a good case could be made that conventional food may be considerably safer.

 My quick summary is organic labeled products are limited to pre-scientific agriculture.

Are natural pesticides better? Definitely, not – though, because natural pesticides are not regulated,  we know much less about their toxicity. Bruce Ames is one of the heroes of environmentalism, so NY Times science writer John Tierney turned to the Ames et al 1999 paper to document his column Synthetic v. Natural Pesticides: the captioned Dietary pesticides (99.99% all natural). This paper is open access, free PDF here, by B N Ames, M Profet, and L S Gold: Division of Biochemistry and Molecular Biology, University of California, Berkeley.

When a toxicologist says “99.99%, by weight, of the pesticides we eat are natural” she is probably referring to this paper. I like the way John Tierney characterizes the Ames work

Dr. Ames was one of the early heroes of environmentalism. He invented the widely used Ames Test, which is a quick way to screen for potential carcinogens by seeing if a chemical causes mutations in bacteria. After he discovered that Tris, a flame-retardant in children’s pajamas, caused mutations in the Ames Test, he helped environmentalists three decades ago in their successful campaign to ban Tris — one of the early victories against synthetic chemicals.

But Dr. Ames began rethinking this war against synthetic chemicals after thousands of chemicals had been subjected to his test. He noticed that plenty of natural chemicals flunked the Ames test. He and Dr. Gold took a systematic look at the chemicals that had been tested on rodents. They found that about half of natural chemicals tested positive for carcinogencity, the same proportion as the synthetic chemicals. Fruits, vegetables, herbs and spices contained their own pesticides that caused cancer in rodents. The toxins were found in apples, bananas, beets, Brussel sprouts, collard greens, grapes, melons, oranges, parsley, peaches — the list went on and on.

Then Dr. Ames and Dr. Gold estimated the prevalence of these natural pesticides in the typical diet. In a paper published in 2000 in Mutation Research, they conclude:

About 99.9 percent of the chemicals humans ingest are natural. The amounts of synthetic pesticide residues in plant food are insignificant compared to the amount of natural pesticides produced by plants themselves. 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.

We have estimated that 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 the 0.09 mg they consume of synthetic pesticide residues.

Even though these natural chemicals are as likely to be carcinogenic as synthetic ones, it doesn’t follow that they’re killing us. Just because natural pesticides make up 99.99 percent of the pesticides in our diet, it doesn’t follow that they’re causing human cancer — or that the .01 percent of of synthetic pesticides are causing cancer either. Dr. Ames and Dr. Gold believe most of these carcinogenic pesticides, natural or synthetic, don’t present problems because the human exposures are low and because the high doses given to rodents may not be relevant to humans.

“Everything you eat in the supermarket is absolutely chock full of carcinogens,” Dr. Ames told me. “But most cancers are not due to parts per billion of pesticides. They’re due to causes like smoking, bad diets and, obesity.”

He and Dr. Gold note that “many ordinary foods would not pass the regulatory criteria used for synthetic chemicals,” but they’re not advocating banning broccoli or avoiding natural pesticides in foods that cause cancer in rodents. Rather, they suggest that Americans stop worrying so much about synthetic chemicals:

Regulatory efforts to reduce low-level human exposures to synthetic chemicals because they are rodent carcinogens are expensive; they aim to eliminate minuscule concentrations that now can be measured with improved techniques. These efforts are distractions from the major task of improving public health through increasing scientific understanding about how to prevent cancer (e.g., what aspects of diet are important), increasing public understanding of how lifestyle influences health, and improving our ability to help individuals alter their lifestyles.

You can read a detailed account of their work in the Handbook of Pesticide Toxicology.