I had several people ask me if I have second thoughts about my berry consumption in light of a swarm of news stories about some pesticide residues in Driscoll berries “exceeding Canada’s safety standards.” I’ve often talked about my breakfast of a mix of blueberries, strawberries, raspberries and bananas smothered in unflavoured Greek yogurt and topped with Fiber One cereal, so the question about my being concerned was not unreasonable.
To cut to the chase, I’m not concerned. I am quite aware of how “Maximum Residue Levels” or “MRLs” are determined and am equally aware of studies that place berries comfortably in the “healthy food” category. I think the benefits of eating berries outweigh any theoretical risk posed by pesticide residues even in the rare instances when these exceed the Maximum Residue Levels. I arrive at this conclusion based on what I’ll call an educated guess because the trial that would give us a conclusive answer cannot ever be done. That would require an experimental group and a control group matched in every possible way with the only difference being the types of berries consumed. One group would consume berries with pesticide residues that exceed the MRLs to the extent that has occasionally been noted, and the other group would eat the same amount of berries with pesticide residue levels always below the MRLs. Furthermore, the two groups would have to be large enough for the results to be statistically significant and would have to be followed for decades since nobody thinks that berries with pesticides that exceed the MRL are going to cause disease today, tomorrow or next week. Such studies are administratively and economically impossible to carry out.
The current issue about “unsafe berries” was sparked by a “whistleblower” who was fired by the Driscoll company supposedly for releasing information about the company knowingly shipping berries to Canada with pesticide residues in excess of the MRL. First item to clarify is that the MRL is a measure of whether a pesticide has been appropriately used and is not a determinant of safety! It does have a safety component, but it certainly is not a “safety limit” that when exceeded presents a risk. The MRL is based on a calculation of the amount of pesticide residue that is ingested by consumers in a realistic diet relative to the “Acceptable Daily Intake (ADI)” which is the amount of pesticide residue that can be consumed every day over a lifetime with no risk of harm. The ADI in turn is based on animal studies in which the maximum dose that causes no harm is determined. This is called the No Observed Adverse Effect Level, or NOAEL. The ADI is then determined by dividing the NOAEL by a factor of 100 to take into account that humans are not giant rats and that the effect on people may be different than on animals.
Now for the task of calculating the MRL. First, the amount of residue that remains on a crop after spraying with a pesticide at the minimum dose that will protect the crop is quantified. Then by taking realistic dietary exposure into account, the amount that can end up being ingested by a person in a day is calculated. The MRL is then set to ensure that the ADI is not exceeded. But remember that the ADI is based on the maximum dose that does not cause an adverse effect in an animal and has a further 100-fold safety factor built in! So, exceeding the MRL cannot be equated with compromising safety. As an example, the highest residue level found in Canadian surveys was for the fungicide captan on blackberries at a level 34 times greater than the MRL. Calculations show that this is still way below the ADI. A 70 kg adult would have to eat about 2 kg of these berries a day to exceed the ADI. Still, if MRLs are exceeded, it does mean that further scrutiny is appropriate because the pesticide may not have been used in the approved fashion. However, exceeding MRLs is rare with studies showing 98% compliance with residue limits. The Driscoll case was indeed a case of non-compliance with some shipments between 2022 and 2024 exceeding the MRLs, something the Canadian government was aware of. There was no recall because while the MRLs were exceeded, the residues did not reach a level that would approach the ADI.
Now for the other side of the coin. Berries contain numerous bioactive compounds, particularly polyphenols that downregulate inflammatory pathways, reduce oxidative stress, improve the flexibility of arteries and reduce the risk of type 2 diabetes. Berries also provide a good dose of fiber. And we have epidemiological studies for evidence of benefit! For example, the U.S. National Health and Nutrition Examination Survey (NHANES) of 37,232 adults found that people reporting regular berry consumption had about a 21% lower rate of all-cause mortality than non-consumers after adjustment for multiple factors.
Related on the SLP
There you have it. MRL’s are not haphazardly determined, they are based on sound science, have a large safety factor built-in and are rarely exceeded. So, I will keep eating my well-washed berries happily.
Joe Schwarcz is Director of McGill University’s “Office for Science and Society,” which has the mission of separating sense from nonsense. He is well known for his informative and entertaining public lectures on topics ranging from the chemistry of food to the connection between the body and the mind. Find Joe on X @joeschwarcz
A version of this article was originally posted at McGill University. It has been reposted here with permission. Any reposting should credit the original author and provide links to both the GLP and the original article. Find McGill University on X @mcgillu
