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Research shows toxins in sewage sludge being spread as fertilizer


March 27, 2008
By Fruit & Vegetable

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Researchers at the Johns Hopkins
Bloomberg School of Public Health have determined that about 75 per
cent of the toxic substance triclocarban,

Researchers at the Johns Hopkins Bloomberg School of Public Health have determined that about 75 per cent of the toxic substance triclocarban, an ingredient in antibacterial hand soap and commonly washed down the drain by consumers, persists during wastewater treatment, ultimately accumulating in municipal sludge that is later spread as fertilizer for crops.

For the study, the Hopkins researchers collected samples from a large urban sewage treatment facility in the eastern U.S. Over a period of weeks, they tracked the mass of triclocarban entering the plant in wastewater and leaving it in reclaimed water and municipal sludge.

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According to the study, the facility was highly effective in removing triclocarban from wastewater. Only about three per cent of triclocarban molecules entering the plant were discharged into surface water along with the treated effluent. However, very little degradation of the triclocarban occurred, due to the compound’s polychlorinated aromatic chemical structure. Approximately 75 per cent of the initial mass accumulated in sludge, where it remained chemically unchanged. Anaerobic digestion reduced the overall sludge volume but not the quantity of triclocarban, thereby concentrating the antiseptic agent to levels several thousand-fold higher than those found in raw wastewater. At the particular plant observed, 95 per cent of the sludge is recycled for other uses, such as being sold as a soil conditioner and crop fertilizer.

More studies are underway to determine if triclocarban can migrate from sludge into foods, thereby potentially posing a human health risk.