Tree bark traces global pesticide spread

By Susan Milius

WASHINGTON, Sept. 28 (UPI): More than 200 bits of tree bark collected from 90 places around the world confirm the theory that Earth's atmosphere acts as a giant distillery, lifting pesticides from warm regions and depositing them in colder places, chemists said Thursday.

DDT and other old-style, organochlorine pesticides travel this way, settling even in areas where they have never been used or have been banned for decades, said Ronald Hites from Indiana University in Bloomington, Indiana.

He and Staci Simonich, now at Proctor and Gamble in Cincinnati, published the results of a global survey in the new issue of the journal Science.

For years, "global distillation was largely a theoretical idea," said Hites. "People have looked at pollutants but in a spotty way."

To get a worldwide picture of pesticide distribution, the researchers e-mailed and wrote far-flung colleagues asking for bark samples. The scientists chose tree bark because its high fat-content would grip the fat-attracting pesticides.

Trees hold their bark five to seven years, said Hites, giving the researchers a long view of what drifted through the air.

Samples arrived in the researchers' Indiana lab from Gorky Park in Moscow, suburban Beijing, the Orinoco rain forest in Venezuela and dozens of other places.

In analyzing them for 22 organochlorine pesticides, the chemists found that concentrations of the most volatile chemicals changed with latitude, supporting the idea of a global distillation effect.

"It really happens -- it's significant," said Hites.

The researchers found Ddt in parts of the midwestern and southwestern United States even though the country banned the chemical in 1973.

Overall researchers found high levels of organochlorine pesticides, volatile and less volatile, in the United States, Europe, India, the Middle East, Japan, Brazil, Australia, Taiwan, South Korea, and Russia.

Low concentrations occurred in the samples from rain forests in Venezuela, Costa Rica, Ecuador and Belize, as well as in bark from the Marshall Islands, Guam, Bermuda, Tasmania and New Zealand's South Island.