Pesticide residues: what about chronic toxicity and accumulation?

In a prior post commenter “L” asked a question that worries a lot of people, especially moms.

I understand that one would need to eat multiple body weights in a day to die right away of acute toxicity, but what about chronic toxicity and accumulation of these substances in the body when consumed not over days but years? (Over several years I will consume multiples of my body weight of certain crops, so what could the consequences be in this case? Higher risk of cancer etc.? And I understand that actual toxicity is different from probabilities/risks in the future.) Thanks

Here’s what I wrote as a comment reply:

Good question. Ewan R’s answer illustrates how large the safety factors are – the ‘tolerances’ set by the EPA. The challenge posed by your lifetime exposure question is “how do we measure that?”. Even if willing to wait a century for the results, the cost of blind, controlled studies would be impossible to fund. Because of the practical impossibility of funding such long term studies, toxicologists developed the “factor of safety”, or some prefer “factor of ignorance”.

Possibly one reason that toxicologists are more relaxed about the cumulative or chronic toxicity issue is that they learn early on that humans have evolved to survive in a toxic world. Our DNA repair mechanisms reflect this constant barrage from background radiation to chemicals. 99.9% of pesticides are natural – the plants have evolved these chemicals because something is always trying to eat them.

For a quick, accessible read, I suggest Steve Savage’s discussion in What Are Your Favorite Toxins?

For further reading may I suggest the B N Ames, M Profet, and L S Gold paper Dietary pesticides (99.99% all natural), whose abstract reads:

The toxicological significance of exposures to synthetic chemicals is examined in the context of exposures to naturally occurring chemicals. We calculate that 99.99% (by weight) of the pesticides in the American diet are chemicals that plants produce to defend themselves. Only 52 natural pesticides have been tested in high-dose animal cancer tests, and about half (27) are rodent carcinogens; these 27 are shown to be present in many common foods. We conclude that natural and synthetic chemicals are equally likely to be positive in animal cancer tests. We also conclude that at the low doses of most human exposures the comparative hazards of synthetic pesticide residues are insignificant.

This lengthy paper is an edited version of a chapter titled ‘Cancer Prevention and the Environmental Chemical Distraction [PDF]‘, in the 2003 book Politicizing Science: the Alchemy of Policymaking. You can pay Amazon $9.99 for the Kindle or you can download the chapter “Cancer Prevention and the Environmental Chemical Distraction” [PDF] on the UC Berkeley site.

Distraction is the right word.