Seed World

Sense, Nonsense and Science: Pesticide Concerns

Over the last few years I’ve spoken at various agricultural conferences and have met many farmers.  But I’ve never heard a comment like: “Gee, I don’t think I’m spending enough money on pesticides, I’d like to spend more.” Or, “is there any way I can increase my exposure to pesticides?” The point of course is that pesticides are expensive and by design are toxic, facts of which farmers are acutely aware. After all, they are on the front lines, and are far more likely to be affected by pesticides than John Q. Public.

Farming is a tough life, it’s hard to make ends meet. No farmer wants to waste money on unnecessary chemicals. They use pesticides simply because they make it possible to produce the hefty amounts of food needed to feed the world. But even with the use of pesticides, and the increased yields they afford, one out of every six people in the world goes to bed hungry every night!  Organic production methods have their place, but they are just too unreliable to feed the masses.

As recently as a century ago, some seventy percent of the population was involved in food production. Today, we rely on about two percent of the population to feed us. And we want them to feed us cheaply and with a wide array of choices. We also want our produce to look good and be available year-round. All that cannot be accomplished without the judicious use of agrochemicals.

Those of us who haven’t had farming experience have little idea of the variety of plant diseases that farmers have to cope with. Leaf blight, leaf scorch, leaf spot, powdery mildew, botrytis grey mould and red stele are just some of the diseases that can affect strawberry plants. Tomatoes can be affected by fungus root rot, grey leaf spot, bacterial canker and late blight. An apple grower has to cope with apple scab, black rot, blister spot, blue mould, bitter rot, bull’s eye rot, fire blight and sooty blotch. But that’s nothing compared with the 51 fungal, 37 viral and seven bacterial diseases that wheat farmers have to contend with. And then there are the insects, nematodes, rodents and assorted weeds that can devastate crops. Each of these problems can be addressed through the appropriate use of specific chemicals. Little surprise then that over four hundred different pesticides are registered for use in Canada!

Dr. Joe Schwarcz

Pesticides increase crop yields, about that there is no doubt. But do they also increase the risk of health problems? As far as farmers are concerned, probably. Parkinson’s disease, some lymphomas and prostate cancer have been associated with exposure to certain pesticides. There’s no iron-clad proof but given the known toxicity of pesticides and the epidemiological evidence, there’s a good chance that we are looking at a cause and effect relationship. Another concern is raised by the hormone-like properties of some pesticides, exposure to which in the womb may have long term consequences. For example, a study of 50 Mexican girls aged eight to ten revealed that girls from a farming community where pesticides were commonly used had earlier breast development and larger breasts than girls from a ranching area where pesticides were not used. All subjects came from the same Mayan population and their families were similar in diet and lifestyle.

Another intriguing study found that the highest rates of birth defects in babies born in the U.S. occur among those conceived in the months from April to July. It is also during these months that levels of pesticides as well as nitrates from fertilizer are at their highest levels in surface waters. Conceivably some of these chemicals may have an effect in utero. Of course, an association like this does not prove cause and effect; pollen in the air or even TV reruns increase during springtime and could be associated with birth defects. But admittedly the pesticide connection is scientifically more plausible.

And yet another interesting finding. Men who work in flour mills tend to father fewer sons than daughters. A study carried out in the state of Washington found 63 per cent of the children born to flour mill workers were girls while in the rest of the state, girls made up 49 per cent of new-borns. Flour mill workers are exposed to a number of pesticides that are used to keep insects and rodents out of stored grain and flour. The idea that pesticides may have an effect on reproduction is not far-fetched. Thirty years ago, dibromochloropropane, a compound widely used at the time to kill nematodes that attack the roots of fruit trees and crops, was banned because it caused sterility in male mammals including humans.

But what does all this mean though for those of us who are not farmers, don’t live in communities where pesticides are extensively used and don’t work in flour mills? We are all still exposed to pesticides through our food, water, air and even kitchen floors. All this exposure combined, though, is orders of magnitude less than that of farmers, or indeed families of farmers. The bottom line? Occupational exposure to pesticides merits continuing investigation, but I will happily keep eating my several apples a day in spite of the fact they may harbour residues of forty pesticides, with an average of four per apple. The amounts in my view are insignificant. But I will add that I have produced only daughters and granddaughters.