Monkeys on the African island of Zanzibar have learned that ingesting charcoal will counteract the adverse affects of toxic substances in their diet, say Duke University and University of Wyoming scientists.

UW Professor David Cooney, a chemical engineer with extensive research on the medical uses of activated charcoal, says he was asked to test samples collected in a study by Duke scientist Thomas Struhsaker, who observed the unusual habit of Zanzibar red colobus monkeys eating charcoal.

Struhsaker was familiar with Cooney's research and with his recent book, "Activated Charcoal in Medical Applications." He sent Cooney leaf samples of the monkey's main dietary source, Indian almond and mango leaves, which are potentially toxic. He also sent charcoal taken from burned trees and charcoal lying near kilns, where it was produced for cooking.

Cooney studied the adsorption ability of five charcoals from Zanzibar in hot water extracts steeped from the Indian almond and mango leaves. Adsorption is the ability of substances, in this case the toxins, to stick to the surface of a solid, such as charcoal.

"For comparison, we also evaluated three commercial powdered activated charcoals," he says. "As expected, these charcoals acted best, yet the African kiln charcoals adsorbed surprisingly well. The findings support the hypothesis that the monkeys eat charcoal to reduce the harmful compounds, which have the potential to be toxic or interfere with digestion."

Struhsaker says the young leaves of exotic trees, consumed by the monkeys living in gardens in this area of Zanzibar, are also high in protein and highly digestible.

"This may explain why the birth rates and population densities of the colobus living in the Indian almond and mango habitat adjacent to the Jozani Forest are significantly higher than those in the ground water forest," he says.

Cooney's book, "Activated Charcoal in Medical Applications," was published in 1995 as a comprehensive reference of research on medical uses of activated charcoal. His and other studies describe activated charcoal's effectiveness in treating overdoses and poisonings in humans and animals.

The collaborative work by Cooney and Struhsaker has been published in two papers appearing in the International Journal of Primatology.

A UW faculty member since 1981, Cooney is the author of more than 80 papers in refereed scientific journals. He served as head of the UW Department of Chemical Engineering from 1983-1990. His academic awards at UW include the Outstanding Graduate Teaching and Research Award and the Outstanding Undergraduate Teaching Award, both sponsored by Tau Beta Pi, the national engineering honorary.