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Public Radio's Environmental News Magazine (follow us on Google News)

Airborne Pesticides

Air Date: Week of

Robin Finesmith of Living on Earth's Midwest bureau at WCPN in Cleveland reports on a recent study published in the journal Science about the appearance of banned pesticides on tree bark, even in remote regions. The study indicates the chemicals travel widely by air, and their persistence in the environment exceeds researchers expectations.


CURWOOD: It's Living on Earth. I'm Steve Curwood. Pesticide residues have been found in many places in the world where they've never been used at all. That's according to a study recently published in Science magazine. It provides important new data on the environmental fate of organochlorine-based pesticides, many of which can cause cancer and hormone disruption. From Living on Earth's Midwest bureau at WCPN in Cleveland, Robin Finesmith reports.

FINESMITH: The study found that pesticides sprayed in one part of the world can travel long distances through the atmosphere and accumulate elsewhere. Ronald Hites and Stacy Simonich of Indiana University found 22 pesticides in samples of tree bark from around the world, including many chemicals that have been banned in the US and Europe for health reasons.

HITES: We found small levels virtually everywhere we looked. Some of the more remote samples were in rainforests from South America, from various relatively pristine areas of Africa. Some of the lower levels were in some remote areas of Australia. Some very, very low levels in the western part of the United States.

FINESMITH: Hites says his findings prove that some common pesticides can vaporize into the atmosphere from warm regions where they're used and be carried to colder regions hundreds or thousands of miles away. In these colder areas the pesticides can accumulate on the ground and in plants and animals. This process, called the global distillation effect, has been suggested before, but hadn't been proven in a large-scale study until now. According to Hites, most of these pollutants are coming from Third World countries in warmer climates.

HITES: I think the major sources tend to be those developing countries, such as India, China, parts of the Middle East, parts of Central and South America, who still use some of these compounds in their agricultural practices. These countries are likely to be important sources to the colder regions of the globe.

FINESMITH: But Hites and Simonich found that some organochlorine pesticides don't evaporate easily and so those are not subject to the distillation effect. This group, which includes the notorious pesticide DDT and the commonly-used endosulfan, tend not to move as vapors very far from where they're used. But in another important result, the tree bark study showed that high concentrations of some of these chemicals can remain in the environment longer than had been thought, even in areas where they've been banned for years. In the United States, for example, breakdown products of DDT were found in agricultural areas of eastern states, the midwest, the southwest, and California.

HITES: We thought that we'd find some residuals in these tree bark samples, but not really as much as we did find. We were kind of surprised to find relatively high levels still in the developed countries. Even 15 to 20 years after the ban, in industrialized countries, these compounds are still around.

FINESMITH: Professor Hites says his and Simonich's findings on the movement of what he calls volatile and less volatile pesticides through the atmosphere can provide useful, long-term lessons to policymakers.

HITES: For the less volatile compounds, the higher molecular weight, chlorinated insecticides, movement through the atmosphere is not a particularly long range process. That was a surprise. Regulations for these non-volatile compounds on a country by country basis could be very effective, which is good news. That's not true for some of the more volatile compounds. In order to reduce the deposition of these compounds to arctic regions, one would really have to ban these compounds all over the world.

FINESMITH: No such ban is under consideration now, though the United Nations is laying the groundwork for international policy recommendations on these chemicals through an international assessment of pesticide use currently being designed. For Living on Earth, I'm Robin Finesmith in Cleveland.



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