Modern pesticides have helped make farming far more productive. But they've also caused countless accidental poisonings. Now, a study suggests that even the routine use of pesticides can pose serious health risks in the long run.
The lifetime toll of pesticides. I'm Bob Hirshon and this is Science Update.
Farmers who work with pesticides, even without major mishaps, have a greater risk of neurological problems. That's according to a study of nearly 19,000 farmers, led by epidemiologist Freya Kamel of the National Institute of Environmental Health Sciences.
They looked at a host of symptoms, ranging from headache and fatigue to memory loss and motor problems. The more pesticides the farmers used in their lives, the greater the risk – even if they hadn't used them recently.
And this is a contrast from previous studies, which have emphasized the importance of recent use.
She says that people who evaluate the safety of these chemicals need to look beyond serious accidents and short-term exposure. I'm Bob Hirshon for AAAS, the Science Society.
Making Sense of the Research
Pesticides, like cars and nuclear power, are one of the great double-edged swords of technology. Without pesticides, the world's farms would require more labor-intensive production. Thus, feeding the growing global population would be more difficult and expensive. However, since pesticides are poisons, they also pose a health risk to humans, other animals, and the environment. The most notorious of all pesticides is DDT, which was banned entirely in 1972 because it was so toxic.
Scientists constantly keep tabs on pesticides to see if they pose an unacceptable health risk. However, as Kamel points out, most studies have focused on the short-term risks. For example, what happens if a person accidentally swallows or inhales the pesticide? What happens if it gets on a person's skin, or in her eyes?
Kamel's study, on the other hand, looked at the effect of simply using the pesticides as directed over a long period of time. The study found that farmers with a higher lifetime exposure to pesticides had more neurological problems – even if they never had a major accident handling the chemicals.
Some of the chemicals these farmers used, like DDT, are no longer on the market, but others remain in use. Some are even found in lawn and garden treatments that people can use at home. However, because the concentrations of the chemicals are lower in home formulas, and because home gardeners tend to use pesticides less often than farmers do, it's hard to say if the general public faces a significant risk.
The researchers also looked at fungicides (fungus-killers) and herbicides (weed-killers), but found no relationship between these chemicals and neurological problems. This doesn't mean that these chemicals are totally safe – it just means that only insecticides (bug-killers) seem to cause neurological damage.
The most powerful aspect of the study is its large size. By looking at the records of 19,000 farmers over a 25-year period, the researchers saw things that might not have been obvious in a smaller group over a shorter period of time. Also, in any scientific study, the larger the sample size, the more accurate the result. The study suggests that if you want to check the safety of any chemical, looking only at accidents gives you just part of the picture.
Now try and answer these questions:
- How is this study different from past studies of pesticides and human health?
- Suppose only farmers who worked with banned chemicals like DDT experienced symptoms. What would that mean?
- If you were starting a career as a farmer, what would you do to limit your lifetime exposure to pesticides? How does that differ from preventing accidental poisonings? Assume you need to use pesticides to make your farm successful.
- On balance, do you think pesticides are a good thing or a bad thing? Explain your answer.
In the National Geographic News Article Environmental Movement at 40: Is Earth Healthier? students can read about the 40th anniversary of Rachel Carson's book Silent Spring, which introduced America to the dangers of pesticides like DDT.
Arctic Life Threatened by Toxic Chemicals, also from National Geographic News, tells of the buildup of pesticides and other chemicals in the animal and human populations of the Arctic.
In the Access Excellence lesson Operation Mexfly, students study the effects of spraying insecticide on the Mexican fruit fly.