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[交流] 【其他】搞农药是应该看看！

World would be a hungrier place without pesticides

Author:JOE SCHWARCZ 2009-10-28 0:00:00

Over the last few years, Ive spoken at various agricultural conferences and have met many farmers.

None of them said things like, "Gee, I dont think Im spending enough on pesticides," or "Is there any way I can increase my exposure to pesticides?"

Pesticides are expensive and by design toxic, facts of which farmers are acutely aware. They are, after all, on the front lines, and far more likely to be affected by pesticides than John Q. Public.

Farming is a tough life; its hard to make ends meet. No farmer wants to waste money on unnecessary chemicals. They use pesticides because they have to in order to produce the hefty amounts of food needed to feed the world.

Still, even with the increased yields afforded by pesticides, one out of every six people in the world goes to bed hungry every night. Organic production methods have their place, but they are too unreliable to feed the masses.

As recently as a century ago, about 70 per cent of the population was involved in food production. Today, we rely on only about two per cent to feed us. And we want these people to feed us cheaply and with a wide array of choices. We also want our produce to look good and be available year-round.

But all that cannot be accomplished without the judicious use of agrochemicals.

Those of us without 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, bulls-eye rot, fire blight and sooty blotch.

But thats 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 more than 400 pesticides are registered for use in Canada.

Pesticides increase crop yields, but do they also increase the risk of health problems?

As far as farmers are concerned, probably. Parkinsons disease, some lymphomas and prostate cancer have been associated with exposure to certain pesticides.
Theres no iron-clad proof, but given the known toxicity of pesticides and the epidemiological evidence, theres 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 age 8 to 10 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 had a similar 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.

And yet another interesting finding: Men who work in flour mills tend to father fewer sons than daughters. A study carried out in Washington state 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 newborns. 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 to kill nematodes that attack the roots of fruit trees and crops, was banned because it caused sterility in male mammals, including humans.

So what does all this mean for those of us who are not farmers, dont live in communities where pesticides are extensively used and dont work in flour mills? We are all still exposed to pesticides through our food, water, air and even kitchen floors. A nationwide random survey showed that almost all kitchen floors had some pesticide residue, mostly from house and garden pest control products. All this exposure combined, though, is orders of magnitude less than that experienced by farmers and families of farmers. The Canadian Pest Management Regulatory Agency sets rigorous maximum residue limits for pesticides on food, based on the best available scientific evidence, with levels being monitored by the Canadian Food Inspection Agency. The great majority of fruits and vegetables are found to contain no residue, and less than one per cent of the residues exceed legal limits.

The bottom line?

Occupational exposure to pesticides merits continuing investigation, but I will happily keep eating my apple (or two) a day, pesticide residues or not.

There are far more important things in life to worry about - like the fact that while youve been reading this column, about 60 people in the world died of hunger.

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