Add Water and Sunshine, get Dioxin

22 April 2003

University of Minnesota researchers have discovered that triclosan, an antimicrobial made by the ton and added to hand soaps, clothing and other personal items, can degrade into a dioxin when exposed to sunshine in water.

Although the species of dioxin coming from triclosan is not especially toxic, the sheer amount of the compound in the system makes this fact worrisome, and it is possible that more toxic chemicals may evolve from triclosan degradation products.

Kristopher McNeill, a chemist and one of four authors of a new article in the Journal of Photochemistry and Photobiology A: Chemistry, studied triclosan in a special aqueous solution: Mississippi River water.

"When we irradiated it with ultraviolet light in wavelengths typical of sunshine, part of the triclosan disappeared, and 2,8-dichlorodibenzo-p-dioxin (2,8 DCDD) appeared in the water," McNeill says.

"The most toxic form of dioxin — 2,3,7,8-TCDD — is 150 00 times as poisonous as the chemical formed from triclosan," McNeill adds, "but it is still a source of concern, because another study by the United States Geological Survey found triclosan to be a widespread pollutant in American rivers and streams that had waste treatment plants."

The fact that triclosan ends up in sewage — because of its many domestic uses — is potentially dangerous, he says, because "our wastewater is often chlorinated, and triclosan may gain Cl atoms and go on to form more toxic dioxins."

Unlike agricultural chemicals such as fertilizers and pesticides, triclosan — a personal care product, not a drug — is not subject to close regulation by US government agencies.

"Triclosan itself is not toxic, and it is fairly rapidly degraded in the environment so it does not appear to be a problem," McNeill says. "Finding this degradation product from triclosan should be a warning to look for what happens downstream to other common compounds whose basic structure suggests that they could be precursors to dioxin or other toxic chemicals."

Douglas E. Latch, Jennifer L. Packer, William A. Arnold & Kristopher McNeill: Photochemical conversion of triclosan to 2,8-dichlorodibenzo-p-dioxin in aqueous solution. J Photochem Photobiol A 2003, Article in Press.

D.W. Kolpin, E.T. Furlong, M.T. Meyer, E.M. Thurman, S.D. Zaugg, L.B. Barber & H.T. Buxton. Pharmaceuticals, hormones, and other organic wastewater contaminants in US streams, 1999–2000: A national reconnaissance Environmental Science & Technology, 2002, 36(6):1202–1211.

-Jonathan Beard