Wednesday, April 24, 2013

The EWG Dirty Dozen: Whoever Said Ignorance is Bliss Definitely Didn't Have Chemistry in Mind

Each year, the Environmental Working Group (EWG) compiles a "Dirty Dozen" list of the produce with the highest levels of pesticide residues on them. The 2013 version was just released this week, framed as a handy shopping guide that can help consumers reduce their exposure to pesticides. Although they do say front and center that it's not intended to steer consumers away from "conventional" produce if that's what they have access to, this strikes me a little as talking out of both sides of their mouth. How can you say that if you really believe that the uncertainties are meaningful enough to create the list, and to do so with the context completely removed? I'm pretty certain the Dirty Dozen preaches to the choir and doesn't change many people's behavior, but the underlying message behind it, while perhaps done with good intentions, to me does some genuine harm regardless. The "appeal to nature" fallacy and "chemophobia" overwhelm legitimate scientific debate, have the potential to polarize a nuanced issue, and tend to cause people stress and worry that's just not all that necessary. This is not hardly going to be a defense of pesticides, but a defense of evidence-based reasoning, and an examination of how sometimes evidence contradicts or complicates simplified narratives. You should eat any fruits and vegetables that you have access to, period, no asterisk.

This latte should not be so happy. It's full of toxins. (Source)
Almost 500 years ago, the Renaissance physician Paracelsus established that the mere presence of a chemical is basically meaningless when he wrote, to paraphrase, "the dose makes the poison." The question we should really be asking is "how much of the chemical is there?" Unfortunately, this crucial context is not accessible from the Dirty Dozen list, because context sort of undermines the reason for this list's existence. When we are absorbing information, it comes down to which sources we trust. I understand why people trust environmental groups more than regulatory groups, believe me. However, one of the recurring themes on this blog is how evidence-based reasoning often doesn't give the answers the public is looking for, whether it's regarding the ability to reduce violent crime by cleaning up lead pollution, or banning BPA. I think a fair amount of the mistrust of agencies can be explained by this disconnect rather than a chronic inability to do their job. However true it may be that agencies have failed to protect people in the past, it's not so much because they're failing to legitimately assess risk, it's for reasons such as not sounding an alarm and looking the other way when we know that some clinical trials are based on biased or missing data. Calling certain produce dirty without risk assessment is sort of like putting me in a blindfold and yelling "FIRE!", without telling me if it's in a fireplace or whether the next room is going up in flames. When 2 scientists at UC Davis looked into the methodology used by the EWG for the 2010 list, they determined that it lacked scientific credibility, and decided to create their own model based upon established methods. Here's what they found:

Out of the 120 items tested, only one even reached 1% of the FDA's imposed limit, and it was only at 2%. Only seven (5.8%) exceeded 0.1% of the limit. Literally, 94% of the "dirty dozen" was below 1/1000th of the FDA limit. Over 75% of the samples contained less than 0.01%, which corresponds to 1,000,000 times below the chronic No Observable Adverse Effect Levels from animal toxicology studies), and 40.8% had exposure estimates below 0.001% of the FDA limit. If you're concerned that perhaps the FDA limits are arbitrary or too conservative, please understand that every pesticide, by regulation under FIFRA, requires extensive acute and chronic toxicity testing, and the residue limit is set at least 100 times less than the established "no effect" level. The EPA periodically reviews new evidence to see if their toxicity classification is still justified, and can pull a pesticide off the market if there's quality experimental evidence that supports making that decision. So yeah, although we discover new things all the time about how chemicals interact with our bodies, when exposures are so negligible, it's sort of a parallel issue. It's just not worth worrying about.

Pesticide residues found on the 2011 "most dirty" produce: celery. Reference dose is the FDA limit. Notice how exceedingly small the exposure is. We're talking nanograms per kilogram of your body weight. (Source: UC Davis study)

On its face, it seems logical that mere presence could matter. After all, these chemicals are designed to kill things. However, as with pretty much everything in life, the reality is a tad bit more complex. Regular table salt kills slugs, but we know that up to a point it enhances flavor without additional health risk. Drinking too much water can friggin kill people. It takes 10 times less copper sulfate, a chemical sometimes used as pest control in organic farming to kill 50% of a test population in rats than the synthetic pesticide glyphosate, so it's possible that using the Dirty Dozen list to buy organic actually points you in the wrong direction from a health perspective. This measurement is called to the LD50, the standard of acute toxicity. If you want to understand risk better, take a look at the table of various chemicals from the LD50 link above, which includes natural and synthetic ones, to get a sense of how we determine how toxic something is. Read about the limitations of the test and make your own informed decision. Using the "appeal to nature" line of reasoning, in which synthetic is inherently bad at any level, is sort of the mirror image of climate skeptics scoffing at the risk of increased carbon dioxide in the atmosphere by proclaiming it "plant food". Context is everything. If you're interested in convincing fence-sitters about the dangers of applying pesticides, preying on chemophobia has the opposite effect you're looking for. If you're really interested in improving the food system or making a positive impact on public health, it's of vital importance to stick to evidence and be up-front about what we do and don't know. People don't respond to alarm very well even when the science totally justifies it, so it stands to reason that people won't respond to alarm when science doesn't really justify it.

There are, of course, a wide variety of pesticides on the market. Some are used because they're specifically good at killing insects, some because they kill weeds, and some are used to prevent fungal infections. Furthermore, each type of pesticide has several distinct classes within them. For instance, within insecticides, there are organochlorides, organophosphates, and neonicotinoids, which all have different biochemical mechanisms for their lethal effects on their targets. So in order to be heed my advice on being up-front about the uncertainties that do exist, I should acknowledge that while the FDA sets limits for individual pesticide residues, it doesn't limit how many pesticides may be used. Often, farmers will apply more than one pesticide on their fields, and we really don't know so much whether small exposures of each simultaneously combines to create more of a health issue than each one individually. Here's a study that suggests an antagonistic effect between DDT and dieldrin, greater than what would have been predicted by just adding the two individually. Both chemicals have been banned in most developed countries for decades, so I'm wondering about how rigorous this study really is by claiming it as part of the French diet less than 10 years ago, but the implication that individually assessing exposures might be insufficient to accurately determine actual health risks in real world exposures is worth noting. This doesn't mean that .0000843 micrograms/kilogram of imidacloprid and 0.000809 of malathion would necessarily combine to create a health hazard, but scientists have not historically looked much into testing it. Prior plausibility would suggest that it's exceedingly unlikely, but it's a legitimate uncertainty.

On the other hand, glyphosate is the most widely used herbicide in the US, and is considered by the EPA to be a toxicity class III pesticide, "slightly toxic" on a scale where class IV is the least harmful. It's only really harmful if you drink a large amount of it. It doesn't bioaccumulate, and it is not harmful to birds, amphibians, and fish in comparison with older pesticides, particularly if it's a formulation without a surfactant called POEA. It kills a wide variety of plants by disrupting a protein synthesis pathway that is specific to plants, and thus does not exist in mammals. Chronic effects have not been observed in animal studies at levels nearly 300 times the FDA limit. Animal studies thus far suggest that it's not carcinogenic, and the EPA considers it to be as such. It is absorbed poorly through the skin, and roughly 30-36% absorbed through ingestion. Two people poisoned by glyphosate (presumably from attempting suicide) had undetectable levels in their bodies after 12 hours. Small exposures do not add up, and large exposures literally go away in a relatively short time frame. If you're familiar with toxicology and/or science-minded, here's everything you'd ever want to know about it, produced by the National Pesticide Information Center at Oregon State University. The FDA doesn't even monitor glyphosate residue on produce because its level of toxicity doesn't warrant it, but if a test were to show my apple has 0.01% of the FDA level of glyphosate on it, I'm confident that it's going to be just fine. I'd rather we have a food system where we don't use it at all, but there's plenty of more pressing health risks that we ignore than those presented by glyphosate.

Pesticides are an artifact of a larger, unsustainable system, in which a combination of better crop management and alternative pest control methods could and hopefully will help reduce our reliance on them for the environment's sake, as well as the health of farmers, their workers, and their neighbors. Some accumulate in the environment and can cause genuine ecological harm. In large concentrations at high doses, some are very toxic, and can cause some permanent conditions in farm workers who mix and apply them. If you're an expecting mother or have an infant, I think it's perfectly reasonable for physicians to recommend avoiding conventional produce as much as possible just to be safe. Infants don't have fully developed systems for detoxifying compounds like adults do, and it's sound advice to be more aware of pesticide residues.

I understand the compelling contrast in imagery, with workers with hazmat suits applying poisons in a massive monoculture field vs. free-range animals juxtaposed against a diverse field and an idyllic farmer. It's really difficult to look at images such as the one to the left and accept that, as the consumer, the evidence clearly and definitively points to negligible health risks by eating the end product. I'd much prefer a smarter, ecologically-friendly food system that more efficiently gets nutritious and safe food to more people, and I'm encouraged that people are increasingly interested in heading there. I go to my neighborhood farmer's market every week during the summer and fall to get organic produce from local farmers for almost entirely the same reasons anyone else does. Once winter rolls around and I want some cheap summer squash, I'm as aware as anyone of all the inputs that went into getting it to the store. Where I differ from most is in my assessment of risk, informed as it is by graduate level toxicology and biochemistry. I'm hardly an expert, but I know a fair amount, and I think it's of vital importance to share it with people. We don't do a very good job of educating people on these subjects, much less science in general, so I almost feel compelled to highlight where our intuition leads us to unwarranted conclusions.

I'm convinced that people respect and respond to intellectual honesty more than they do fear, because fear so often comes from a not-so-rational place with crucial pieces of the puzzle missing. This opens itself up to an avalanche of conflicting information, which just confuses people and drives them to dig in to their preferred version of reality. People aren't robots, but the tools to avoid all of this are out there. It'd be totally boss if more people were aware of them, and we could confront misconceptions that arise because of how poorly we educate people in chemistry. Now, if we could just do something about all that 2-Oxo-L-threo-hexano-1,4-lactone-2,3-enediol in citrus fruits.

UPDATE 4/26/13: So, this thing is going around a lot lately. It's a paper that claims glyphosate might be behind a whole host of common diseases like inflammatory bowel disease, obesity, depression, ADHD, autism, Alzheimer's disease, Parkinson's disease, ALS, MS, cancer, etc., I guess because it's a "textbook example of exogenous semiotic entropy" (WTF?!). This should raise red flags anyway, but you should really download it just for fun to see if you can make any sense of it. I guarantee you, it won't come easy. It's possibly the most bizarre academic paper I've ever read. Unfortunately, Reuters uncritically covered it, and even called it a "study", which it most definitely is not. It's a review full of pseudoscientific assertions, and although the authors say they did a "systematic review", they clearly don't quite grasp what that means. Which, I suppose, is probably why a paper involving issues of toxicology and biochemistry ends up in a fairly obscure physics and information science journal.

In a word, "no". Just "no".


  1. Great article. Question--what about the info that came out a couple of weeks ago about glyphosate being a contributing factor to colony collapse disorder in bees? Do you think those "studies" are valid and worth listening to?

    1. Thanks! I actually hadn't seen anything about glyphosate and CCD. I've sorta been following the link between neonicotinoids and CCD, and there was a paper that came out a couple of weeks ago purporting to show that it's the primary cause that made a pretty big splash.

      With neonics, there's obvious direct biological plausibility that they could be the primary cause, but I don't think it's been demonstrated that it's more than one of several possible contributors as of yet. With glyphosate, the link would be more indirect because it's an herbicide rather than an insecticide. It's certainly plausible that glyphosate would disrupt bees' foraging, but the evidence appears to be pretty much non-existent. Glyphosate has also been used for way, way longer than CCD started to appear, so that would have to be convincingly explained somehow.

      Ultimately, I don't like to dismiss many things completely out of hand unless they violate fundamental laws. Even something without a known mechanism, like that retracted Seralini study on Roundup Ready corn causing cancer could be worthwhile if the methods and analysis were legit.

  2. I really appreciate your expertise and insight. Thanks for this informative post. I have a question regarding your commentary about conventional produce pesticide residue. I am sure you're familiar with Dr. Bruce Ames. I am speaking specifically to his commentary regarding naturally occuring rodent carcinogens present in a cup of coffee that would exceed the amount of pesticide residue fron conventional produce eaten over a year and whether that statement is accurate and as a result would you recommend that pregnant women avoid even decaffeinated coffee.
    Thanks in advance for your response.

    1. Thanks! Yep, that Dr. Ames quote has been around for years, and the idea that the vast majority of pesticides we ingest occur naturally is quite well established. I really have no expertise to be giving advice on what pregnant women should and should not avoid, but there's a few things to consider at least, and I guess the best I can do is lay out my thought process on it and let people be their own judge.

      Personally, I wouldn't particularly worry about decaf coffee too much, and if my partner asked about it, I'd say I can't really see where it'd be necessary to avoid as a rule. I suspect Dr. Ames's comments are a bit of a rhetorical exercise to combat the appeal to nature fallacy more than raising a red flag on the uncertainty we face every day from coffee.

      If caffeine doesn't present a clear and unacceptable risk in pregnancy after years of research on it, especially when limited to 1-2 cups a day, I'd imagine decaf would be even less of a risk, just going by it being the most present alkaloid in regular beans. But if I were talking to a pregnant woman avoiding all coffee while she was pregnant, I wouldn't really consider that a totally unreasonable thing, and certainly not a choice worth me trying to persuade differently. There's not really a downside to avoiding it, and probably not much of a downside to drinking it. It's a personal choice that wouldn't register on my "things I can't bite my lip on" radar.