Pesticides in Fruits and Vegetables

[jsolomon]

If you were to believe every hyped story out there, you would expect to see bodies littering the streets.

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I do! Only problem is, the buggers are out walking around where I want to ride my BIKE!

[jsolomon]

I find it extremely alarmist-weenie that the people who wrote this article doing all of their great science don't mention:

(1) The methodology used to detect the pesticides

(2) The pesticides detected and their levels

(3) The relative toxicity of that amount compared to the size of a representative human (say 50 kilos for an arbitrary, meaninful value)

So... I'm going to drink another cup of the top contender in mutagens, teratogens, and carcinogens from Patrick S's list and not worry. I'm more likely to die from having some methamphetamine-dependent 16-year old cream me with his car while I'm riding my bicycle.

BTW, some of those pesticides, like the organophosphate class cause really odd symptoms when you're toxic on them, so you'd know if you were getting a significant dose. Alarmist psuedoscience.

[docsconz]

Interesting in that it was announced earlier this week that human life expectancy in the US has increased again.  The obvious inference is that chemicals and pesticides in food are good for us...

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Imagine how much better we would be without the chemicals and pesticides in our food

Now I am not generally a person who prefers something simply because it is "natural". After all, many poisons are natural. However, one potential advantage of many "natural" i.e. non-synthetic "pesticides", especially ones inherent in the plants we have been eating for generations, is that our gene pool may have adapted to those particular plant defenses. Indeed many, such as the chemical capsaicin, have become culinarily desirable in their own right. I doubt that will happen with too many synthetic pesticides.

[=Mark]

Now I am not generally a person who prefers something simply because it is "natural". After all, many poisons are natural. However, one potential advantage of many "natural" i.e. non-synthetic  "pesticides", especially ones inherent in the plants we have been eating for generations, is that our gene pool may have adapted to those particular plant defenses. Indeed many, such as the chemical capsaicin, have become culinarily desirable in their own right. I doubt that will happen with too many synthetic pesticides.

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I find it highly ironic that peppers started producing capsaicin to scare off hungry mammals whose complex digestive systems destroy the seeds, only to have seemingly irrational humans becoming perversely attracted to the pain they produce. As a result, a fairly innocuous plant indiginous to a small area of central America has now been spread to 6 of 7 continents with thousands of variant strains in less than 500 years. Pretty successful reproductive strategy...

[Patrick S]

Now I am not generally a person who prefers something simply because it is "

natural". After all, many poisons are natural. However, one potential advantage of

many "natural" i.e. non-synthetic  "pesticides", especially ones inherent in the

plants we have been eating for generations, is that our gene pool may have adapted

to those particular plant defenses. Indeed many, such as the chemical capsaicin,

have become culinarily desirable in their own right. I doubt that will happen with

too many synthetic pesticides.

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Doc, I have nothing but the fondest feelings for you, so please don't take it personally if I take a moment to disagree with the idea that we humans have developed adaptations to natural plant pesticides that make them less harmful to us than synthetic pesticides.

First, and probably most important, the plants most of us eat on a regular basis simply have not been a part of the human diet for very long. In fact, agriculture in general is a very, very recent development when seen in the context of all human prehistory. For most of us, our diets of plants is very different today than it was even 500 or 1000 years ago. Gold et al(p. 28) put it very well:

Humans have not had time to evolve a “toxic harmony” with all of the plants

in their diet. The human diet has changed markedly in the last few thousand years.

Indeed, very few of the plants that humans eat today (e.g. coffee, cocoa, tea,

potatoes, tomatoes, corn, avocados, man goes, olives, and kiwi fruit) would have

been present in a hunter-gatherer’s diet. Natural selection works far too slowly

for humans to have evolved specific resistance to the food toxins in these

relatively newly introduced plants.

After all, we still can get cancer from viruses, sunlight, heavy metals, certains foods, stuff we've been exposed to from the beginning.

Secondly, adaptation is always reciprocal between predator and prey, in this case plants and the animals that feed on them. This is the concept of the evolutionary 'arms race.' Adaptation is met with counteradaptation. Just as there is selection pressure for the animal to develop resistance to the plant pesticides, there is also selection pressure for the plant to develop a counter-adaptation to the predators adaptation. If it were really possible that animals (whether ourselves or plant pests) could develop perfect resistance to plant defenses over time -- then there would be no such thing as endogenous pesticides, because none of the chemicals would still be effective as pesticides! I don't think I've explained this very well, but what I'm trying to say is that the plant is adapting to its predators just as much as its predators are adapting to it. If it stopped doing that, it would cease to exist.

Thirdly, the toxicological evidence doesn't seem to support the idea that natural pesticides are less harmful than synthetic pesticides. In particular, I'd point you to chapters 5 an 7 in the Gold et al paper I linked to above. Chapter 5 addresses the "misconception" that "the toxicology of synthetic chemicals is different from that of natural chemicals," while chapter 7 addresses the "misconception" that "synthetic chemicals pose greater carcinogenic hazards than natural chemicals." Gold et al give what I think is a masterful and completely convincing refutation of the idea that natural chemicals are less harmful than synthetic ones. I'll give a brief summary of some of their points, but you'd really have to read their paper and their references to understand all of their arguments.

One point they make is that our defenses against toxic substances are general rather than specific to each chemical. Many of the same mechanisms our body uses to protect us against natural toxins also protect us against synthetic ones. This is a very important point.

Humans have many natural defenses that buffer against normal exposures to

toxins (Ames & al. 1990b); these usually are general rather than tailored to each

specific chemical. Thus, the defenses work against both natural and synthetic

chemicals. Examples of general defenses include the continuous shedding of cells

exposed to toxins—the surface layers of the mouth, esophagus, stomach, intestine,

colon, skin, and lungs are discarded every few days; DNA repair enzymes, which

repair DNA that has been damaged from many different sources; and detoxification

enzymes of the liver and other organs, which generally target classes of toxins

rather than individual toxins. That defenses are usually general rather than specific for each chemical makes good evolutionary sense. The reason that predators of plants evolved general defenses presumably was to be prepared to counter a diverse and ever-changing array of plant toxins in an evolving world: a herbivore that had defenses against only a set of specific toxins would be at a great disadvantage in obtaining new food when favored foods became scarce or evolved new toxins.

The most remarkable toxicological finding, though, in my opinion, is this: in standard in vivo rodent carcinogenicity tests, a similar proportion of synthetic and natural chemicals are found to be carcinogens. This is really amazing to me, and of course completely contradicts the "common knowledge" that natural chemicals as a group tend to be "safe" while synthetic chemicals as a group tend to be "dangerous" on a weight-for-weight basis. The Carcinogenic Potency Database shows that 79 out of 194 commerical pesticides, or 41%, are carcinogens in high-dose rodent tests, while 37 out of 72, or 51% of natural pesticides tested so far have turned out to be rodent carcinogens in the same tests (see p. 32 in Gold et al). There are actually estimated to be about 10,000 natural pesticides and their breakdown products in our diet, but only recently has anyone began testing them. Again, the whole idea that synthetic chemicals are somehow fundamentally different in terms of toxicology just doesn't seem to be true.

One last thing on this subject -- I'd highly recommend anyone interested in this stuff check out the HERP index in Gold et al's article. HERP stands for Human Exposure/Rodent Potency. Basically this is a ranked index of various carcinogenic hazards. The ranking is straightforward. It reflects the ratio of the dose humans recieve in mg per kg of body weight to the dose in mg per kg that has been shown to be carcinogenic in rodent tests. So, for instance, if you are eating 10mg per kg of body weight per day of chemical X, and the rodent tests show that chemical X causes cancer in rodents at doses of 100mg/kg/day, then the HERP rank for that chemical is 10%. The methodology is described in detail in Gold et al's papers on the subject.

Now, what is amazing is how high on the index many natural chemicals are compared to the synthetic chemicals that are usually the focus of concern. For instance, caffeic acid from coffee has a rank of 0.1%, caffeic acid from lettuce has a HERP of 0.04%, and hydrazine from mushrooms has a rank of 0.02%. All pretty low, right?

Well, now compare these HERP values to the HERP values for the synthetic pesticide residues. For instance, DDT and its metabolites have a HERP of 0.00008%. The highest HERP ranking for any synthetic pesticide of pesticide breakdown product is for ethylene thiourea, a breakdown product of certain fumigant, which has a HERP of 0.002%. Ethylene dibromide (EDB), a fungicide which was banned due to concerns of residues, had a HERP of 0.0004%. Toxaphene had a HERP of 0.0001%, chlorobenzilate a HERP of 0.0000001%. And these are at the synthetic residues with the highest HERP rankings.

In that light, it seems very odd indeed that we spend so much on synthetic residue monitoring, but no one bothers to test produce for levels of endogenous, natural pesticides which are present in much higher amounts and are just as likely to be carcinogenic. I mean, I have yet to hear anyone demand that we allocate any significant resources to monitoring caffeic acid levels in lettuce and potatoes, or allyl isothiocyanate in mustard, or benzene, 1,2,5,6 dibenzanthracene, 4-methylcatechol, isoprene and benzo(a)pyrene in roasted coffee, or glutamyl-p-hydrazinobenzoate in mushrooms, or 8-methoxypsoralen in celery, etc, etc, ad infinitum.

Darcie B: Edit to add: One last thing, I think we can all find data to support any claims.

And that is where science comes in. Claims are a dime a dozen. The trick is going out into the real world and accumulating the data you need to actually test any given claim. The claim that survives the observational tests survives, and those that don't . . . don't. It can be hard work evaluating which claims are true and which aren't, but certainly it is possible.

=Mark: Interesting in that it was announced earlier this week that human life expectancy in the US has increased again. The obvious inference is that chemicals and pesticides in food are good for us...

Not only is life expectancy up, but both the incidence of cancer and the death rate from cancer has dropped. The incidence of some types of cancers have increased, but the overall incidence and death rate from all cancers has decreased. See:

Jemal et al, 2004. Annual report to the nation on the status of cancer, 1975-2001, with a special feature regarding survival. Cancer 101, pp.3-27.

And in any event, epidemiological studies have long shown that those who eat the most fruits and vegetables --and who are thus exposed to the highest levels of synthetic pesticide residues-- have significantly lower rates of cancer. That doesn't mean that the residues are responsible for the protective effect, of course, but it does seem hard to reconcile with the idea that the residues are a significant risk factor for cancer.

Its been fun, yall!

Edited March 11, 2005 by Patrick S (log)

[Patrick S]

Now I am not generally a person who prefers something simply because it is "natural". After all, many poisons are natural. However, one potential advantage of many "natural" i.e. non-synthetic  "pesticides", especially ones inherent in the plants we have been eating for generations, is that our gene pool may have adapted to those particular plant defenses. Indeed many, such as the chemical capsaicin, have become culinarily desirable in their own right. I doubt that will happen with too many synthetic pesticides.

←

I find it highly ironic that peppers started producing capsaicin to scare off hungry mammals whose complex digestive systems destroy the seeds, only to have seemingly irrational humans becoming perversely attracted to the pain they produce. As a result, a fairly innocuous plant indiginous to a small area of central America has now been spread to 6 of 7 continents with thousands of variant strains in less than 500 years. Pretty successful reproductive strategy...

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Same thing with delta-9-tetrahydrocannabinol! Cannabis produces this stuff (presumably) as a deterrant, yet today we have millions of cannabis enthusiasts worldwide (over 100 million people worldwide who have tried it), cultivating and breeding these plants for the highest THC content.

[docsconz]

Doc, I have nothing but the fondest feelings for you, so please don't take it personally if I take a moment to disagree with the idea that we humans have developed adaptations to natural plant pesticides that make them less harmful to us than synthetic pesticides.

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Patrick, No offense taken. This is one of the most brilliant posts I've ever read on eGullet! Your post is absolutely cogent, well researched and extremely well written. As I said, I am not one to generally assume that "natural" is necessarily better. It would be difficult in my field of medicine to think that way and it certainly is not borne out in practice. You have managed to make me rethink my view of pesticides, at least as far as human health is concerned. Of course, that is only one potential consequence of synthetic pesticide application. Other potentially more significant consequences involve the effects intended or otherwise on the environment and the very balance of predator-prey adaptations you discussed.