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Sunday, May 20, 2018

A Revised Assessment of 2016 USDA Pesticide Residue Detection Data

On March 25 and May 10th I posted articles about the USDA’s annual Pesticide Data Program (PDP) that takes a look at chemical residues on various commodities in the US food supply (mainly fruits and vegetables).  I described the program and its various levels of published summaries as a valuable example of a transparent data resource, which it certainly is.  Unfortunately I made an error in my analysis, using the wrong year’s “sample table” (10,365 rows) to identify which of the residue detections in the “results table” were from organic or conventional sources (31,981 rows drawn from a 2.2 million row table).  This meant that I erroneously overstated the number of pesticide detections on organic samples.  I had reported an average of 2.6 detections/organic sample and the actual number is 0.75 detections per sample vs 3.2 detections/sample for conventional.  Journalist Tamar Haspel brought this issue to my attention.  She was skeptical about the similarity of detection frequencies I had described for organic and made the effort to check the original data.  I very much appreciate her persistence on this question.  I want to apologize for that error and any wrong conclusions that came from that.  I do this analysis of the data each year as a personal project unrelated to my consulting and ag communications jobs, so the responsibility for this error rests entirely on me.  I am striving to remove the content that was based on the error, let people know about the mistake, and with this post, get the analysis right. (Revised Forbes posts here and here)

Fortunately there is no change in the most fundamental conclusion that should be drawn from the USDA’s data: our food supply and particularly the fruits and vegetable are very safe and so we can all enjoy them and benefit from their health-promoting characteristics.  This is fully true for both organic and conventional options.  What also remains true is that analytical chemists are capable of finding tiny trace levels of chemicals, but finding those does not mean something is dangerous.

So, what has changed based on getting the data right is that the data shows a distinctly lower number of synthetic pesticide detections on organic samples (~1/4 as many).  That fact has to be balanced with the reality that there are many natural pesticides commonly used on organic farms, which are not detectable with of the testing technologies used in this particular USDA program.  For the most part these materials have very low mammalian toxicity, but that is also true for a great many of the synthetic pesticides that are part of the testing.  Conventional farmers also use these same pest control options, but possibly not as extensively as would be needed in organic production.  Again, if there was testing for these particular pesticides, it would almost certainly do nothing to change the paradigm of overall safety of the food supply.

Although there were more residues detected per sample for conventional vs organic (3.2 vs 0.75 detections/sample), there are similarities in the distribution of those residues in terms of level relative to conservative, EPA tolerances

One retained conclusion that is of interest is that 80% of the residues detected on conventional crops are at levels low enough so that they would not be considered as a violation of the organic rules because they are 20 times lower than the EPA tolerance.  In the case of organic (for which this statistic is 84%) the assumption is that the presence of such low level residues is “inadvertent.”  For conventional it means that by following the EPA label requirements, growers can even exceed the safety factors for which those requirements were designed through a rigorous risk assessment process by EPA. 

The data does show that even though there are fewer residues detected on organic, 16% of those are of synthetic chemicals at levels that exceed what is acceptable under the organic rules (the corresponding number for conventional is 20%).  This certainly does not represent any kind of health risk, but it isn’t consistent with the organic “brand” or with the convenient fiction that organic means “no pesticides.”

Finally, the Environmental Working Group’s “Dirty Dozen List” remains a misleading and science-free publication.  It is corrosive for trust in the food supply and if believed, has the potential to make consumers pay more than they need to, or even worse, be less likely to consume the quantity of fruits and vegetables that health experts would recommend.

Once again, I apologize for my earlier error with the data.