Tuesday, July 26, 2011

Toxics: The Long Term, Low Dose Question

(This post first appeared on Sustainablog on 7/26/11)

Each year, the USDA generates an extensive set of data which demonstrates that modern American consumers face no real threat from toxic pesticide residues on their food.  This is particularly true in terms of "acute toxicity," or short-term poisoning.  Someone would have to eat thousands to millions times their own body weight to kill themselves with produce.

To many people, that still leaves a troubling question:  "what about long term exposure to low doses of toxic chemicals and combinations of those chemicals?" This question is more difficult to answer.

What We Can't Know about Toxins and Our Health

When my son was small, he would often answer questions by saying, "I can't know."  In a way, that is where we sit on the "long-term, low-dose question."  Based on the testing that we can practically afford, wee "can't know"  all the long term outcomes where the rates of cancer or other chronic diseases might be in the range of 1 per million people or less.  We can do a good job of predicting which chemicals are reasonably potent carcinogens and the like, because such toxicity can be detected in a relatively short term feeding study at fairly high rates of the chemical.  Those tests give us a good deal of protection from truly dangerous substances, but it is not really possible to answer the "low-dose, long-exposure" question with this sort of test.  Does that mean that we have to live in fear of the trace levels of man-made chemicals that are in our water and in our food? No.  Here is why.

What We Can Know

Just because we can't answer this question using rats in a laboratory does not mean we are without encouraging "data."  This comes in the form of common life experience, and from what we know about protective chemicals in nature.

Want to Avoid All Toxics? Good Luck With That

I have often seen people write that they are trying to "avoid all toxics" in their life.  That is actually impossible. Almost all the foods we eat contain naturally toxic chemicals that are made as defense mechanisms by the plants or animals in question.  These toxins are present at levels which are too low to cause us any problem in the short term.   But what about the fact that we are consuming low, mixed doses of dozens of natural toxins every day?    Few of these chemicals have ever been evaluated for any kind of chronic toxicity.  What if we ask the "long-term, low-dose" question about these chemicals?
The calm response is to realize that our bodies are well equipped for living in a moderately toxic world. The cells of our skin and in the lining of our digestive track only live a few days before they are replaced.  That minimizes the potential to become cancerous because of exposure to toxins.  We also have powerful liver enzymes that chew up toxins of all kinds.  On the whole our bodies do a great job of dealing with the wide variety of toxins that we eat at low rates.  The same is true for both natural and man-made toxins.

Don't Forget About The Good Chemicals

The other encouraging bit of information is that we are far from helpless when it comes to maintaining our health while eating small doses of toxic substances.  It turns out that fruits and vegetable are excellent sources of other special chemicals which help us to fight cancer and a host of other ills.  Many people turn to the poorly regulated "supplements market" to get these chemicals, but that is not necessary.  The much more natural option is simply to enjoy the diverse and relatively low cost produce which is available to us today.  The bonus is that these products taste great and also provide basic minerals, vitamins, and fiber in our diet.  I will list just five examples of the foods which help to protect us against a wide variety of chronic diseases:
  • Tomatoes: the largest dietary source of lycopene - a chemical that reduces risk of cancer, osteoporosis and cardiovascular disease
  • Grapes: resveratrol in red grapes and wine enhances cardiac health
  • Berries: berries have extremely high levels of various antioxidants that reduce the risk of cancer, improve urinary tract health, and help with memory and healthy aging
  • Asparagus: rutin in asparagus can ameliorate the effects of diabetes and lower blood pressure among other benefits after the body converts it to quercetin-3-glycoside
  • Broccoli: contains lots of vitamins A and C, but also isothiocyanates which stimulate the enzymes in the body that neutralize many potential cancer causing substances
There has probably never been a human society with such ready access to the foods that can protect health and counteract the effects of toxins - natural and man made.  That is why it is tragic when something like the "Dirty Dozen List" discourages significant numbers of people from buying fruits and vegetables.  These consumers then fail to get the very phytochemicals which could protect them - both from the trace chemicals they fear, and from the fearsome chemicals they may not even appreciate (e.g. aflatoxin).

Putting This In Perspective

I am not just saying: "Don't Worry, Be Happy."  There are very real toxic threats in the world - both man-made and natural.  We need to pay attention to what the toxicologists and public health experts tell us.  What we don't need to do is to worry inordinately about trace levels of pesticides or about low levels of most natural compounds.  What we do need to do is to eat our fruits and vegetables!

Vegetable market image from a trip I took to Switzerland a few years ago
You are invited to comment here or to email me at savage.sd@gmail.com


  1. In defense of EWG, they encourage people to buy organic those on the "Dirty Dozen" list and they explicitly state "Eat your fruits and vegetables! The health benefits of a diet rich in fruits and vegetables outweigh the risks of pesticide exposure. Use EWG's Shopper's Guide to Pesticides to reduce your exposures as much as possible, but eating conventionally-grown produce is far better than not eating fruits and vegetables at all."

    However, I'm wondering how accurate it is after reading one of your posts on the "Dirty Dozen." Its not the first time it has been questioned for accuracy either

  2. Anonymous,
    Although I'm glad that EWG says "eat your fruits and vegetables," I don't think that sort of generic, sound advice does very much to counter their main message - that you should be seriously scared about xxxx.

    It seems to me that this is in some large part a marketing tool for Organic (and the financial connection between EWG and Organic marketers is murky). I don't think it actually works very well if that is the goal. The only study I've seen on this topic suggests that the EWG's list mostly just inspires consumers to eat less produce.

    I'm glad that you have seen others questioning the "science" behind the dirty dozen list. There are many and for good reason.


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