There are certain things you can count on with the coming of spring. Two of the earliest are the arrival of the first Mexican and Californian strawberries in the produce aisle and the Environmental Working Group’s (EWG) annual “Dirty Dozen” report misrepresenting the risks of eating said strawberries. I have previously written about EWG’s reporting of risk but want to address them again because there is more to say about their approach to science communication.

For those not familiar with EWG, they are an organization partially funded by organic food trade organizations and organic producers. Absolutely coincidentally, each year they produce a list of fruits and vegetables they feel have excessive pesticide residues while simultaneously suggesting that consumers rely instead on more expensive organic alternatives for their fruit and veggie choices.

Sadly for science communication, their annual Dirty Dozen report regularly gets picked up by news outlets desperate to draw readers to their sites. This week I found over a dozen links to this report including ones from the Vancouver Sun, The Province, and The National Post.

In reading the Dirty Dozen report the first thing to understand is analytical chemists are extremely good at identifying infinitesimally small concentrations of discrete chemicals in mixtures. As I pointed out in a previous post; analytical chemistry has become so precise that a modern mass spectrometer can distinguish to the parts per trillion range. That would be 1 second in 30,000 years. When an activist report says they found “detectable” concentrations of a pesticide in a sample you should take that claim with a grain of salt since that same analysis has the capacity to find a single grain of salt on a 50 m stretch of sandy beach.

As a specialist in risk assessment, the first thing I look for in a report like the Dirty Dozen is the identified concentrations. They will tell me the true story about whether there are any real risks. The absolute tip-off about the Dirty Dozen report is that it does not present actual concentrations for the pesticides identified in the fruits or vegetables in the report. All they say is that pesticide residues were identified.

There is a simple rule of thumb in risk communication. If a toxicological report doesn’t give you the concentrations of a compound it is because the authors don’t want you to see those concentrations. This is not the sort of thing that happens by accident.

But that is not the only way in which the report keeps their readers in the dark. In toxicology, risk is dependent on exposure concentrations and professional toxicological bodies determine acceptable exposure concentrations through detailed, publicly-available, peer-reviewed research. The EWG reporting doesn’t even use toxicological terms in their reports, instead referring to their preferred concentrations as “benchmarks” without ever explaining what that term actually means.

Most importantly, they never explain the basis for their benchmarks. They don’t explain how they determine whether a concentration is safe or not safe. Their calculations have not been widely shared but they don’t appear to be based on the peer-reviewed toxicological literature. The best I can tell is that the values are arbitrary. Consider their benchmark for glyphosate. On their page How Does EWG Set a ‘Health Benchmark’ for Glyphosate Exposure? they write:

EWG calculated a health benchmark for the total amount of glyphosate a child might ingest in a day. EWG’s benchmark is 0.01 milligrams per day significantly lower than both the Environmental Protection Agency’s dietary exposure limit and California’s No Significant Risk Level.

There is no rationale provided to justify or support their benchmark.

For the record, the EPA has systematically (and publicly) reviewed the peer-reviewed toxicological research for glyphosate and has identified a safe dietary limit of 70 mg/day. California, which has a standard based on slightly different criteria, says a safe number is 1.1 mg/day. EWG’s undocumented benchmark (the one they use in their reports) is orders of magnitude lower than the levels identified as posing no significant risk based on the peer-reviewed toxicological literature. To my eye, EWG simply chose the lowest detection limit available from their research lab as the basis of their benchmark.

What the above tells you is that when EWG says something isn’t safe it is not based on the peer-reviewed science. That is not how good science works. In toxicology you don’t just get to declare something is not safe without explaining how you came to that conclusion. Consider a thought experiment:

Imagine that I, a highly credentialed scientist, created my own private “benchmark” for trip hazard risks. Imagine I claimed that individual grains of sand on the sidewalk represented dangerous trip hazards to children. Now it is generally understood that children don’t trip over individual grains of sand but the grains are detectable on the sidewalk if you look carefully enough. Imagine I then wrote a report indicating that the presence of grains of sand on the sidewalk posed a real and dangerous tripping hazard to neighborhood children and suggesting that families buy expensive leaf blowers to protect their children from these unsafe conditions. Does anyone imagine I could get dozens of media outlets in Canada to publish a story on my report detailing the risk of individual sand grains and promoting the sale of leaf blowers? Of course not, because unlike the toxicology every parent in Canada would recognize that my “benchmark was invalid.

Now I would love to write a snappy conclusion to this blog post but happily a peer reviewed academic journal beat me to the punch. As Winter and Katz wrote in their review of an earlier edition of the Dirty Dozen report (in Dietary Exposure to Pesticide Residues from Commodities Alleged to Contain the Highest Contamination Levels):

In summary, findings conclusively demonstrate that consumer exposures to the ten most frequently detected pesticides on EWG’s “Dirty Dozen” commodity list are at negligible levels and that the EWG methodology is insufficient to allow any meaningful rankings among commodities.…our findings do not indicate that substituting organic forms of the “Dirty Dozen” commodities for conventional forms will lead to any measurable consumer health benefit.

Given the above I only wish Canadian content providers recognized when they were being played and stopped giving EWG so much free earned media coverage every year.

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