Breast Cancer

Do Pesticides Cause Cancer? — Experts Explain

Published Oct 29, 2018

It seems so simple. Exposure to pesticides can increase the risk for some types of cancer. The established cancer community seems to agree.

Just to be clear, a pesticide is a poison put on plants to kill bugs.

So why isn’t something being done to reduce our risk of exposure to pesticides? Answering that question runs us headlong into how difficult it is to prove that any one thing specifically causes cancer.

“Establishing that a given agent causes a health outcome is close to impossible; even the relationship between cigarettes and lung cancer took decades to establish,” says Dr. Melissa Furlong, an environmental health expert from University of Arizona College of Public Health.

Let’s start with a comparison. Heart disease. Higher cholesterol increases the risk of heart attacks. We can measure your cholesterol and tell you whether it’s at a safe level or at a level where your chances of a heart attack are greater. And what’s really important, we can be pretty sure that the high cholesterol, and not something else in your life, caused or contributed in a major way to the heart attack. And we can prove by lowering cholesterol we can reduce heart attacks.

Now take pesticides and cancer. We know from animal studies that pesticide exposure increases cancer risk. But we don’t have the same kind of evidence in humans. We don’t have studies of a large number of people who are exposed to pesticides, and followed many years to see if they developed cancer. And we don’t have studies, like they did with cholesterol, which show that reducing the level of exposure to pesticides reduces the risk of cancer.

In heart disease, you could give one group of people with high cholesterol a drug that lowers it and give another group a placebo. You can’t do a study and expose a large number of people to pesticides, and follow over the years to see if they developed cancer. It would be unethical. And there’s no drug you can give that lowers the level of pesticide. So you are left with animal studies which are not as convincing as human studies.

Dr. Furlong says studies of large groups exposed to pesticides  aren’t convincing because they show an “association” – but they don’t prove that the pesticides caused the cancer. And you can’t rule out other factors that might have caused someone’s cancer. Was it their diet, their genes, their lifestyle? You can do a study in animals which rules out these confounding factors, but Dr. Furlong says “those results are in animals, not humans, and we can never be sure that something will work the same way in humans as they do in animals.”

But the problem of proof isn’t limited to medical studies. “There’s a great deal of political push back to determining something is an environmental carcinogen, because of the regulatory applications and the economic implications that that implies,” says Dr. Arch Carson, associate professor of environmental and occupational health sciences at the University of Texas School of Public Health in Houston.

Just like the makers of cigarettes, the manufacturers of pesticides have battled in court over claims that their products cause cancer. And in the United States, Dr. Carson says you need to prove in court “beyond a shadow of a doubt  that a substance is hazardous and has caused harm.”  This extremely high standard is used not only in courts but also by government agencies. The standard of proof is higher than in Europe where you don’t have to prove a substance causes cancer in order to regulate it.

The high bar for proof is what makes the recent case of a $250 million judgment against the maker of a pesticide so significant. The jury awarded a groundskeeper regularly exposed to a pesticide made by Monsanto $250 million in compensation for his non-Hodgkin’s lymphoma. The jury concluded that the cancer was caused by the pesticide. The judge has reduced the amount of the damage award. Carson says this case will likely lead to many other cases of people claiming their exposure to pesticides caused their cancer.

But there’s no indication that this case is going to lead in any new restrictions on pesticides. So as long as there is the possibility of exposure, people have to decide for themselves what they can do to reduce their risk.

“The easy answer is ‘buy organic,'” Dr. Furlong says. She also says “the Environmental Working Group issues a list of the dirty dozen, which are fruits and vegetables with the highest loadings of pesticide residues, and you can either try to buy those organic or opt for fruits and veggies that tend to be cleaner.” Dr. Furlong says what you do with your produces is also important. “Washing and soaking produce is also effective, and studies in China have shown that longer soaking times for produce are associated with lower pesticide metabolites in urine.”

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