Posted on behalf of Richard A. Lovett
Scientists have found that a common antibacterial agent in household hand soaps has a “strong” tendency to accumulate in fish.
The chemical, known as triclocarban (TCC), is added to many antibacterial soaps as part of the developed world’s ongoing preoccupation with germs. As soapy water goes down the drain, it carries TCC into sewage treatment plants not designed to eliminate it, and from there into the environment. When waterways in the US are tested for TCC, more than 60% show up positive, Ida Flores, a toxicologist at the University of California, Davis, said today at a meeting of the American Chemical Society, in Anaheim, California.
But nobody had looked at whether the molecule might bioaccumulate in fish living in these waterways.
To find out, Flores put hatchling medaka fish (Oryzias latipes – a 4-centimeter aquarium fish commonly used in toxicity studies) in 500 mL beakers containing 20 micrograms per liter (20 ppb) of TCC – a level which she describes as “in the upper range” of those that have been measured in contaminated rivers.
What she found was that the fish indeed accumulated TCC from the water – quickly in fact. “Within five minutes, levels of TCC in the water had decreased,” she says, adding that this is a sign that the fish were taking it up.
Rolf Halden, an environmental scientist at Arizona State University who in 2004 helped develop the analytical methods needed to detect trace levels of TCC in rivers and lakes, agrees.
“I applaud the authors,” he says, noting that the find supports recent work by his own team, which has found TCC bioaccumulation in aquatic worms and earthworms. “Within seven years, TCC has risen from a pollutant overlooked for half a century, to one of the most prevalent, persistent, toxic and bioaccumulative personal care product ingredients tracked by the scientific community and regulatory agencies,” he says.
That’s a disturbing discovery, but not unexpected, says Melissa Schulz, a chemist at The College of Wooster, Wooster, Ohio, who notes that fluoxetine (Prozac) does the same thing, and TCC’s chemistry makes it more likely to do so than fluoxetine.
But it’s nevertheless an important find, because her own studies have found that mixes of TCC and a related chemical, triclosan at roughly comparable levels can change fish reproductive behavior by making male fathead minnows (Pimephales promelas) less willing to defend nest sites against invaders.
Flores study didn’t stop with finding that TCC bioaccumulates. She also found that within hours the fish began metabolizing it into other chemicals, excreting them into the water.
On first consideration that sounds like a good thing, since it means the fish are getting rid of the compound. But it may not be that simple because the metabolites themselves might be a problem. “It depends on how biologically active TCC metabolites are,” says Shultz.
Another problem, Shultz says, is that the chemical might “biomagnify” up the food chain, meaning that as large fish eat smaller ones, they might become increasingly contaminated, possibly as far up the food chain as human meal tables. “If it is accumulating in fish tissue, there is a chance for TCC to biomagnify,” she says.
Meanwhile, Schulltz says, the next step is to see what happens if fish are exposed for longer durations than 24 hours.