27 April 2006
Persistence Of Triclocarban Surprises
by Kate Melville
Johns Hopkins researchers have been measuring levels of the antibacterial hand soap ingredient, triclocarban, as it passed through water treatment facilities and found that 75 percent of the ingredient washed down household drains persists during wastewater treatment. Worse still, the chemical accumulates in municipal sludge, which is later used as a fertilizer and soil conditioner for crops.
"The observed persistence of triclocarban is remarkable," said researcher Jochen Heidler. "In the [treatment] plant, the chemical contained in sludge underwent biological treatment for an average period of almost three weeks, yet very little degradation took place."
One of the researchers involved in this new study, Rolf U. Halden, had previously published findings on the high levels of both triclosan and triclocarban found in rivers and streams across the country. And now, the discovery that triclocarban is not broken down in water treatment plants has compounded Halden's concerns. "Triclocarban does not break down easily even under the intense measures applied during wastewater treatment. Triclocarban is leading a peculiar double life. Following its intended use as a topical antiseptic, we are effectively and inadvertently using it as an agricultural pesticide that is neither regulated nor monitored."
While the treatment plants were quite effective at removing the triclocarban from the wastewater, the chemical became concentrated in the residue sludge. According to the study, published in Environmental Science & Technology, very little degradation of the triclocarban occurred, with around 75 percent of the initial mass remaining chemically unchanged. While anaerobic digestion reduced the overall sludge volume, it did not affect the quantity of triclocarban, thereby concentrating the antiseptic agent to levels several thousand-fold higher than those found in raw wastewater. Worryingly, 95 percent of the sludge is recycled for other uses, such as soil conditioners and crop fertilizers.
"The irony is twofold," said Halden. "First, to protect our health, we mass-produce and use a toxic chemical which the Food and Drug Administration has determined has no scientifically proven benefit. Second, when we try to do the right thing by recycling nutrients contained in biosolids, we end up spreading a known reproductive toxicant on the soil where we grow our food. The study shows just how important it is to consider the full life cycle of the chemicals we manufacture for use in our daily life." Halden added that additional studies are underway to determine if triclocarban, which is toxic when ingested, can migrate from sludge into foodstuffs, thereby potentially posing a human health risk.
Source: Johns Hopkins University Bloomberg School of Public Health