By Tamar Haspel
May 21, 2018
The Agriculture Department recently released the latest measurements of pesticide residues in our food, in the form of the 2016 Pesticide Data Program results, so it seems timely to talk pesticides and organics.
And bias.
I’ve been following these issues for a long time, and I’ve seen a lot of evidence that organic foods have lower levels of pesticide residues than conventional foods, so I was surprised to read a two-part analysis on Forbes.com by Steve Savage, a conventional-side plant scientist I know and respect, showing that the number of residues, and the amount of pesticide in those residues, were virtually the same for organic and conventional foods.
What could be happening in our food supply for the difference in pesticide levels to narrow so markedly? That would make an interesting column, I thought.
So I started asking people, but nobody had a good explanation. There’s no evidence for widespread fraud (although there’s evidence for some), and the only other explanation was drift. Because organics are often grown in the proximity of their conventional brethren, drift happens. But that’s an awful lot of drift.
And then I talked with Sonya Lunder, senior analyst at the Environmental Working Group. She’s also a data geek, a woman after my own heart, and she had actually tried to replicate Savage’s results. She couldn’t.
So I figured I’d better try to do it myself. And I couldn’t, either.
The reason we couldn’t was that Savage’s data were spectacularly wrong. He reported that conventional foods had an average of 3.1 different pesticides, and organic had 2.6. The real numbers, which I downloaded the entire residue database to get, are 3.2 for conventional (okay, that’s close), and 0.8 for organic (definitely not close). I called the USDA to make sure I hadn’t screwed something up, and it confirmed my numbers. This was an honest mistake, and when I pointed it out, Savage immediately checked for himself, confirmed the error and set about retracting the articles. He told me he felt terrible for getting it wrong.
When I make a mistake — and we all do — I find it to be just about the most humbling experience going. And, naturally, the mistakes we make tend to be in a direction that supports our worldview. Savage is vociferously anti-organic (he boycotts it and works as a consultant for the conventional sector), and perhaps that made it easier for him to believe what his bad data were telling him.
Now that we know what isn’t true about pesticide residues, let’s move on to what is.
One big shortcoming of the research is that some of the most-used chemicals — on both conventional and organic farms — aren’t tested for. Copper sulfate is used widely as an organic fungicide, and I haven’t been able to find any data on residue levels. Glyphosate, the most-used herbicide in conventional agriculture, is just beginning to be tested. (It’s not in the USDA data, but California testing found that of 308 samples, only four had residue, all well below legal limits.) The vast majority of the substances the USDA tests for are only used in conventional agriculture, so it’s not surprising that conventional foods have more residue.
I’d love to see a truly comprehensive study of residues. (If you’ve got one, send it my way!) Still, I have never seen an analysis comparing conventional and organic that didn’t conclude that organic foods had significantly lower pesticide levels.
The key question, of course, is whether that matters, and this is the crux of the disagreement over residue levels.
There’s no question that pesticides can be toxic to people, and farmworker exposure is a serious issue. But levels in food are very low, and the USDA and the Environmental Protection Agency (along with many toxicologists I’ve spoken with over the years) say you shouldn’t be concerned about them.
Not everyone has faith in those assessments, and skeptics often point to the fact that our government agencies haven’t done the kind of testing that can predict the potential danger from long-range, low-level risk from a mix of many chemicals.
There are two ways a mix of pesticides could be dangerous. The first is if they have synergistic effects — that is, the result of the two or more chemicals together is different (and worse) than the results of each individually. The second is cumulative, the long-term exposure of low doses over time.
I spoke with David Eastmond, toxicologist at the University of California at Riverside. “We have seen synergistic effects,” he told me, “but they’re uncommon-to-rare, and they happen at high doses.” A 2008 report made the same assessment, as did University of Copenhagen professor Nina Cedergreen , who published a recent paper on the subject. We should be more concerned with the cumulative effects, the paper concluded.
The EPA does require testing for chronic exposure, and it takes into account the exposure we get to chemicals with similar modes of action, but it is, of course, impossible to test every combination. Cedergreen wrote to me in an email that the disentangling of the effects of pesticides in humans is “very difficult” but that they’ve given it a shot. She co- wrote a paper, published in January, that concluded that the cumulative risk to your average Danish adult from pesticide exposure was equal to that of drinking one glass of wine every three months. I’d sure like for someone to do the same assessment for Americans, but this gives us an idea of the magnitude of the risk.
There is, however, one class of pesticides that came up as a concern over and over, in my reading and interviews: organophosphates. It’s a highly toxic class of chemicals, and the EPA has already restricted the use of some of them. One, chlorpyrifos, has been the subject of a battle between environmental groups, which want it banned, and the EPA, which doesn’t. Unfortunately, the USDA testing doesn’t have large enough sample sizes to tell us which foods are most likely to have residues, but overall organophosphate use has gone down in the United States. In the 2016 data, only one out of about every 300 samples tested had chlorpyrifos residue.
It’s certainly possible for pesticide residue levels to be high enough that they pose a health threat. But in high-income countries, where these things are regulated and tracked, it’s unlikely. Not only should American parents not worry about feeding our kids fruits and vegetables, we should also try to get them to eat as many as possible, conventional or organic. But the risk isn’t zero, and our ability to assess it isn’t perfect.
“The issue of residues is very emotional,” says Nate Lewis, organic farmer and farm policy director for the Organic Trade Association. “It’s a futile effort to try to convince a consumer they’re wrong about their choices.” Although farmers, both organic and conventional, are using pesticides in compliance with the label, and growing safe food, he says, “If the consumer wants to choose something to avoid that [residues], they should be able to make that choice, right or wrong.”
He goes on to say, “I don’t like the narrative that organic is pesticide-free. It’s not. They do use things that are toxic to the environment.” But Lewis has spent more than a decade as an organic inspector and farmer, and he adds: “I’ve seen that organic farmers are very judicious in their use of pesticides. Their goal is to choose the least-toxic approach possible to reduce environmental impact, and pesticides are a last resort.” Twenty-five synthetic pesticides are approved for organic use (compared with more than 900 in conventional ag), and the toxicity of all pesticides used is reviewed by the National Organic Standards Board.
As for the health risk, “It’s critical you stop short of saying it’s going to be healthier for you,” he says. “We don’t know that.”
I’ve spoken with Lewis several times over the years, and I admire his candor and circumspection. Given the human inevitability of mistake-making, I try to do likewise by keeping a mental Post-it note saying, “Hey, this might be the thing you’re wrong about.” On good days, it helps me be less dogmatic about the things I believe, and better at listening. On bad days, I just ignore it and dig in. On the whole, though, I think it makes it easier for me to be more generous in disagreement and harder to be seduced by things I wish were true, but aren’t.
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