Tiny portions of pesticide can cause big problems

April 26, 2002 - Two years ago this spring I wrote a column about the cosmetic use of pesticides on our lawns and gardens. Since then, many communities in Canada have adopted strict guidelines on the use of these poisons and the Supreme Court of Canada has even upheld their right to do so. But the vast majority of pesticides are used in agriculture, and new studies are showing that they can have startling effects.

The latest issue was raised by a recent article published in the prestigious journal Proceedings of the National Academy of Sciences, U.S.. It reported that one of the most heavily used pesticides in the United States (and Canada, Australia and other nations), atrazine, turns male frogs into hermaphrodites - creatures with both male and female sex organs.

Atrazine is an "endocrine disrupter" which means it can inhibit the production and function of hormones. To test how it affects amphibians, researchers at Berkeley, California, raised tadpoles of the African clawed frog (a common research amphibian) in several tanks with water containing from 0.01 parts per billion (ppb) to 200 ppb of atrazine. Tadpoles developed normally in the control tank without atrazine, but researchers found that tadpoles exposed to 0.1 ppb or more of the pesticide developed abnormal sex organs up to 20 per cent of the time (it was repeated 51 times). Some animals grew up to six sex organs. And male frogs exposed to 25 ppb experienced a 10-fold drop in testosterone - to levels below those of normal female frogs.

The findings may be part of the explanation as to why amphibians are in dramatic decline in many parts of the world. Although atrazine does not kill the frogs outright, it could reduce their ability to reproduce. Indeed, field examinations of native frogs in atrazine-contaminated areas have also revealed an unusual level of reproductive abnormalities.

Until recently, atrazine was considered a fairly safe herbicide. It is primarily used in agriculture to control weeds, especially on soybeans, corn and other important crops. It's a very effective broad-spectrum killer and has been used for 40 years in 80 countries worldwide. Because its use is so widespread in North America, there are few areas that are completely free of the chemical. A study by the U.S. Geological Survey, for example, found atrazine in every one of 36 river basins it studied. In some farming areas, atrazine has leeched into groundwater, contaminating drinking water supplies. It's even been found in rainwater at levels that far exceed limits recommended for drinking water (3 ppb) by the American Environmental Protection Agency.

Luckily for humans, we don't spend our lives in atrazine-contaminated water. And since the herbicide doesn't accumulate in human tissues, it's unlikely that its effect on humans would be nearly so dramatic as it has been on frogs. Still, researchers say that the herbicide could be subtly affecting sex hormones in humans. Such concerns have already prompted several European countries including France, Germany and Italy to ban atrazine. France banned it, and related triazine herbicides, last fall after finding degraded atrazine products in more than 50 per cent of French groundwater supplies.

Widespread use of pesticides and herbicides is considered standard practice in modern farming. It's part of the reason why we have such bountiful yields today. But studies have shown that for some crops there are ways to achieve similar yields without the detrimental effects many pesticides have on ecosystem and even human health. We need to embrace these alternatives and combine them with the best of modern techniques if we are to create a sustainable agricultural system for the 21st century.

To discuss this topic with others, visit the discussion forum.