Antibacterial Sludge

Antibacterial Sludge

Today, it's hard to find dishwashing liquids or hand soaps that don't advertise their "antibacterial" chemicals. But while it's unclear whether these chemicals actually help us, there's new reason to believe they might do more harm than good.


The health risks of a germ-killer. I'm Bob Hirshon and this is Science Update.

Triclocarban, or TCC, is a toxic chemical that you might use every day. It's an anti-bacterial agent found in hand soaps and other toiletries, and Americans go through a million pounds of it every year.

Professor Rolf Halden and intern Daniel Paull, of the Johns Hopkins School of Public Health, recently went looking for TCC in six rivers and streams around Baltimore. Using a new technique, they measured concentrations up to twenty times higher than previously reported.


And that was disturbing. But more worrisome was what we found out when we studied the fate of this chemical, during wastewater treatment.

He says it winds up in an organic sludge that's often used as a fertilizer—which means it could end up in crops and eventually, people.

The irony is that chemicals like TCC probably aren't very useful in soaps, since they're rinsed off before they have a chance to work.


So essentially we barely use them for the purpose they're designed for, and then they're discharged into the wastewater and then cause secondary problems.

The health risks this poses to humans is still unknown. But, since farms use billions of pounds of this sludge every year, Halden says it's high time we tested for TCC in their soils. I'm Bob Hirshon for AAAS, the Science Society.

Making Sense of the Research

This study shows that just because something sounds like a good idea doesn't mean there isn't a downside. It's no wonder that antibacterial chemicals like TCC have become so common in American consumer products. Who wouldn't choose a soap that advertises itself as "antibacterial" over an ordinary soap? Nobody wants bacteria on their hands, dishes, or countertops, right?

But in reality, just because something has an antibacterial chemical in it doesn't mean that it's actually better at fighting bacteria. In lab tests, chemicals like TCC have been proven to kill bacteria, but it's not like a tiny speck of the chemical can kill millions of bacteria instantly. The chemical has to be concentrated enough, and in contact long enough with the bacteria, to do its work. Next time you wash your hands, count how long you wait before rinsing your hands off. It's probably less than ten seconds—maybe even less than five. Is that long enough to let an antibacterial chemical do its job?

So whether or not these chemicals do what they're supposed to is highly questionable. And while Halden's team is concerned about their potential effect on the environment and public health, the biggest worry of all is that we simply don't know what these chemicals are doing to us. Rat studies have shown that TCC causes a kind of blood poisoning and interferes with reproduction, but very little is known about its effect on humans. What's more, prior to this study, there was little indication that TCC was finding its way into rivers and streams. Because of that, not much work has been done to track its possible environmental effects. Now, Halden's numbers suggest it's one of the top ten chemicals from drugs and personal care products in the environment.

But the levels of TCC in sludge from wastewater treatment plants might be the most disturbing statistics of all. Most of this sludge is made of organic waste that breaks down in the soil or dissolves in groundwater. TCC doesn't do that. Furthermore, the TCC in the sludge is much more densely concentrated than TCC in the wastewater itself.

Every year, American farmers use 12.5 billion pounds of this sludge to fertilize their soils. That's enough to fill 125,000 railroad cars—a train so long it would reach all the way from Baltimore to Miami. When you think of all that chemical-filled sludge spreading over the soils that grow your family's vegetables, it's easy to get worried. But again, scientists simply don't know how dangerous the situation really is. There simply hasn't been enough interest or money to study the problem. Halden hopes that his findings will turn that trend around.

Now try and answer these questions:

  1. What is TCC?
  2. How could TCC end up in humans, even if it's filtered out of our drinking water?
  3. How does this study change your perception of antibacterial products?
  4. Do you know of other chemicals in household products that might pose a threat to the environment? Are these chemicals necessary? Why or why not?
  5. What question do you think Halden's next study should ask? Propose an experiment that might answer that question.

For Educators

The Alliance for the Prudent Use of Antibiotics is a non-profit organization devoted to the conservation of antibiotics for the most critical purposes.

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