Evidence too weak to link pesticides to cancer - yet
Published Thursday, November 13, 2008 8:18AM EST
TORONTO - It's one of those thorny issues that keeps cropping up among scientists, health-advocacy groups and the public: do the myriad pesticides that farmers use to grow our food cause cancer?
The answer? Nobody is really sure.
At least that seems to be the consensus of world experts who gathered in Toronto on Wednesday for a two-day conference hosted by the Canadian Cancer Society.
Studies in lab animals exposed to various bug, weed and rodent killers show a few do appear to cause some types of cancer, said Aaron Blair, an expert in occupational pesticide exposure at the U.S. National Cancer Institute.
But figuring out whether the chemicals - both synthetic and naturally occurring - affect people in the same way is harder to pin down, he said. For one thing, studies on humans can look only for possible associations between exposure to a substance and a health outcome like cancer.
While some studies have found an apparent excess of certain cancers, such as lymphomas, in farmers and other populations that have high contact with pesticides, the evidence "is not exactly, completely solid in every respect," Blair said in an interview.
"Now you look at occupational studies that have been carried out in various groups who apply or use or manufacture pesticides, and my take on the evidence is it's, well, maybe or possibly."
But scientists aren't about to leave the question hanging, he said.
"The evidence is strong enough, interesting enough from occupational groups with pesticide exposure to make us think there may be these very specific links, where we (need to) do the more precise and better studies."
The question of pesticides' possible role in causing malignancies is a sensitive and pressing issue for the Canadian Cancer Society, which organized the conference to tap into expert opinion and advice so it can better guide Canadians.
For years, the society has called for bans of pesticides for cosmetic use, primarily the chemicals aimed at ridding lawns and gardens of insects and weeds.
"So if it's not OK on lawns and gardens, what do you say about everything else?" said Heather Logan, the organization's director of cancer control policy and information.
The hope is that expert opinions gathered from the conference will help the society frame its advice to Canadians when it comes to pesticide exposure, whether it's the farmer spraying corn from a tractor, people living near agricultural land or the vast majority of us that eat fruits and vegetables that likely carry chemical residues.
The issue of fruit and vegetable consumption is particularly tricky, since the society and other health-advocacy groups strongly advise people to eat plenty of both daily to prevent certain cancers, among them colorectal cancer.
"Ultimately, the bottom line that Canadians need to hear at this point is that eating a healthy diet full of a wide variety of fruits and vegetables is a known way to reduce your risk of chronic disease, including cancer," Logan said. "So that message today is definitely not changing."
"But hearing about standards set about pesticide residues in foods we eat ... and enforcement practices in place through CFIA (the Canadian Food Inspection Agency), we need to make sure those systems are as safe as they possibly can be."
Connie Moase, a director with the pest management regulatory division of Health Canada, said the agency sets minimum residue limits for both domestically grown and imported foodstuffs, based on a battery of animal toxicity studies.
"The acceptable limit is hundreds to a thousand times lower than where we don't see any toxic effects in the animal studies," she said, noting that there are more than 700 registered pesticides that must meet Health Canada standards.
"The food that we're eating is safe, absolutely," said Moase, noting that "at this point, there's certainly no definitive link" between pesticide use and an increased risk for cancer.
Still, lack of proof hasn't stopped some people, worried about what pesticides might do to their bodies, from turning away from conventionally grown foods - as evidenced by the growing demand for organic produce.
As to what the Cancer Society will advise Canadians, Logan said that, for now, it's a question of balancing risk and benefits, erring on the side of caution and choosing the least amount of pesticide exposure until more is known about their effects.
While no one needs a dandelion-free lawn, she said, people do need fresh, affordable produce to maintain good health.