S. Geological Survey published a widely circulated study of chemicals in surface water, in which triclosan was found in 58 percent of natural waters tested. Its median concentration was 0.14 parts per billion; the maximum was 2.3 ppb. McNeill and Arnold chose to study triclosan because they could tell from its structure that it would likely break down in sunlight.

In their study, McNeill and Arnold added triclosan to river water, shined ultraviolet light on the water, and found that between one percent and 12 percent of the triclosan was converted to dioxin.

"The fact that this conversion can happen in surface layers of rivers may not cause harm by itself, but it suggests that more serious reactions--leading to more toxic forms of dioxin--may also happen when triclosan enters the environment," said Arnold. "We want to determine if this is the case." As a first step in sorting out the relations, if any, between triclosan and more toxic dioxin, McNeill and Arnold plan studies to determine whether they tend to occur together in natural waters.

The researchers said that even low levels of very toxic dioxin are worrisome because dioxin readily accumulates in organisms and becomes more concentrated in tissues as it moves up the food chain.

The study was funded by the U.S. Geological Survey, through the National Institutes of Water Resources. Triclosan is manufactured by Ciba-Geigy.

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Contact: Deane Morrison
morri029@umn.edu
612-624-2346
University of Minnesota
14-Apr-2003

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