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The toxic secrets of fresh fruits and vegetables

Investigating potential behavioural abnormalities in mammals caused by agricultural pesticides
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Pesticides can have nicotine-like effects if consumed through food contamination. PHOTO COURTESY OF WUZEFE
Pesticides can have nicotine-like effects if consumed through food contamination. PHOTO COURTESY OF WUZEFE

The health benefits associated with plant-based diets have greatly contributed to the increasing popularity of vegetarianism. Fresh produce, nuts, and whole grains help maintain a balanced intake of nutrients, and vegetarian diets have been linked to health benefits such as lower risks of diseases, like diabetes or some cancers. 

However, while plant-based diets are widely considered healthy, few wonder whether their ‘detox smoothies’ containing fruits and vegetables might be toxic. That’s because apples, celery, strawberries, spinach, grapes, and kale are a few of the products that are the most likely to be contaminated with pesticides, according to a recent publication by the Environmental Working Group. 

David Hampson, a professor at U of T’s Department of Pharmacology & Toxicology, spoke about his research on pesticides and their effects on developmental disorders in mice in an interview with The Varsity.

Pesticide use and oversight

A data analysis study from 2020 revealed that significant long-term insecticide use is common in farming areas that produce fresh fruits and vegetables, since they are more susceptible to insect infestations than other crops. Yet, it would be dangerous for any residue of these insecticides to end up in our food. 

According to the Canadian Census of Agriculture, between 1981–2016, Canadian farms have increased in size and so has the use of pesticides. In Canada, both conventional and organic farms are permitted to use pesticides, so switching to buying solely organic produce doesn’t work as a simple solution to avoid pesticide-treated crops altogether. 

Although Canada is one of the largest exporters of some of the world’s major food crops, the systematic documentation and analysis of pesticides on Canadian farmland is limited. The rise of modern agricultural technology has complicated the collection of accurate information on the amount of pesticide used by farmers in Canada.

The impact of neonicotinoids

The most widely used class of pesticides in the world is neonicotinoids. As the name of this type of pesticide implies, they are known to mimic the toxin nicotine.

Not only are neonicotinoids toxic to insects, they have a detrimental impact on other organisms as well. For example, there were reports a few years ago about neonicotinoids killing bees.

“[That problem] stimulated a lot of research — there were a lot of papers published on [the] toxicity of neonicotinoids to bees,” said Hampson. He noted that the toxic effect of pesticides on everything — not just the organisms they target — can be a big problem. When asked just how damaging neonicotinoids may be to human health, Hampson said that, as with every harmful substance that affects humans, wildlife, and everything else, what matters is how much of the substance we’re exposed to and how long we’re exposed to it.

Unfortunately, IMI is persistent in plants and soil. This means that residue from these pesticides could end up in our food, especially fruits and vegetables. 

Hampson shared his previous experience working in a pesticide analysis lab in the US Food and Drug Administration that screened imported food from foreign countries. Despite only screening a tiny fraction of the products being imported into the US, he said that they picked up all kinds of contaminants, including pesticides, in their analyses. In Canada, domestic and imported foods are sampled for pesticide residue to ensure that they don’t exceed the maximum residue levels established by Health Canada scientists, and to ensure food safety for everyone.

Behavioural changes after exposure to neonicotinoids 

Hampson initiated a study to examine behaviours in young adult mice treated with low doses of a type of neonicotinoid pesticide during their fetal and postnatal development. Hampson and his team wanted to learn whether exposure to insecticides during early development caused long term changes in mouse behaviour. 

The researchers began to treat mice with relatively low doses of neonicotinoids during pregnancy and their nursing period for a couple of weeks after the birth of their babies. Blood analysis detected altered blood chemistry in the young mice, even though they were not exposed to the pesticides after they were weaned. This revelation suggests that there may be permanent consequences for pesticide exposure in early development.

Although this study focused on quantifying behavioural changes in mice caused by neonicotinoids, the results of the behavioural tests they conducted on IMI-exposed mice coincided with the effects of nicotine. 

Researchers observed weight loss due to elevated motor activity and patterns of hyperactivity among tested mice — symptoms commonly associated with nicotine use in humans. “The bottom line is that for all the behavioral tests, our results are more or less similar to what you would see if you had given nicotine [to the mice],” said Hampson.

The lower body weight and antidepressant effects of neonicotinoids may sound enticingly convenient — but are they good for human health? 

“Anything that we’re exposed to, where it’s changing our body biochemistry and our behavior, is probably not a good thing,” said Hampson. He added that if the chemicals introduced withdrawal symptoms similar to those associated with nicotine, discontinuing exposure to them could cause long-term effects as well.