Pesticides are Complicated

I finally finished Pesticide Biotransformation and Disposition (you can see the few public notes I made, usually while riding the bus, here). It’s really more of a reference work but it’s given me a better grasp of the breadth of the question. As a side-effect, I’m even more annoyed at the simplification from anti-pesticide groups that dominates public perception of pesticides.

After reading this book, it seems all of the following are basically true:

  • All pesticides are harmful to some creature, at some dose. Otherwise we wouldn’t call them pesticides — but that doesn’t necessarily mean they are harmful to humans.
  • Pesticides are just chemicals and many chemicals that aren’t thought of as pesticides have similar classes of behavior.
  • Many pesticides aren’t harmful to humans at low doses.
  • Some are.
  • Some pesticides will cause a harmful effect in some humans at one dose that others won’t be affected by (due to genetics, age and other considerations).
  • Some pesticides will increase harmful activity of another pesticide.
  • Some pesticides will inhibit harmful activity of another pesticide.
  • Some pesticides will decrease production of chemicals in your body that you need.
  • Some pesticides will increase production of chemicals in your body that you need.
  • Either could be harmful, sometimes depending on how old you are, your genetics, etc.
  • Sometimes the pesticide itself directly causes harm. Sometimes the pesticide reacts with something in the body and the by-product causes harm.
  • Various chemicals that react with pesticides are produced at varying levels in different parts of the body so a pesticide may be harmful in one part of the body but easily made harmless elsewhere.
  • A pesticide could have an effect in an animal that doesn’t happen in humans1
  • How often you’re exposed can matter a lot.
  • How a pesticide enters the body can change how it might affect you.
  • Commonly used house-hold products (e.g. sunscreen) can increase skin absorption of some pesticides. Clothing can also affect how pesticides are absorbed.

And a lot I’ve forgotten. That’s why I bought the book. Out-of-brain memory.

My own emotional reaction is interesting. On one hand, I realize that I’ve been a bit cavalier in my beliefs about the likely non-harm from pesticides2 and feel a bit foolish (I cringe to re-read some older blog posts). On the other hand, anti-pesticide groups and individuals tend to conflate all risks from all pesticides into one big pile of “BAD”3. Having a slightly more clear idea how complicated it is, the fear-mongering about pesticides annoys me even more. It’s hard to have rational risk discussions about whether harm from a particular pesticide is worth it for the benefits4 when at least some consider any risk too high5.

I don’t know what the answer is but at least I have a reference to research further on particular pesticides as they come up instead of assuming they’ll behave just like another one I’m more familiar with. :)


  1. A good example here is a nasal cancer in rats from repeated exposure to alachlor which doesn’t appear to be likely in humans because rats metabolize the pesticide into a pre-cursor to the actually carcinogenic compound at rates much higher than humans do.

  2. At doses I’m likely to experience — which is near nothing for currently applied ones since we don’t often use pesticides in the home and most food products actually have very little — my risk is still probably pretty small. But probably not as small as I like to think, especially when considering DDT and by-products are still heavily part of our environment.

  3. Studies about occupational studies are too often used to make claims about the superiority of organic food. Or the harms of long-banned pesticides such as DDT are used to make claims about other pesticides thought to be safer.

  4. Relatedly, there is a problem of attention. Which pesticides get attention (research into safety, environmental effects, etc.) is driven by public and private interests and concerns. The current concerns with neonicotinoid pesticides and EFSA’s recent report on them make me wonder if any useful, widely-used pesticides would survive scrutiny. Are other pesticides seen as safe simply because we haven’t looked hard enough for risks?

  5. There is also the problem that many non-experts believe that anything that hurts insects must be dangerous to humans.

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