Investigative journalist Carole Bass has written extensively about nanotechnology, emphasizing how little we know about the risks associated with the nanoparticles now used in a wide range of consumer products, from sunscreen to stain-resistant clothing. Her latest piece, in the new issue of E Magazine, includes an exploration of what these particles do when they wash off our skin and clothing and go down the drain:

[Cyndee] Gruden, a civil engineering professor at the University of Toledo in Ohio, is tackling part of that last question by looking at the effects of two nanometals—titanium dioxide and zinc oxide, used in sunscreens, paint and other products—on bacteria.

Metals “can be toxic to microorganisms,” she notes. “In fact, that’s specifically what they’re for” in consumer products: to inhibit mold, mildew and other nastiness. But when nanometals make their way to a sewage treatment plant, Gruden worries that they might harm the beneficial bacteria that break down what’s delicately known in the business as “biosolids.”

Her preliminary findings, which she presented at a meeting of the American Chemical Society (an academic group, not an industry organization) in March, are mixed. Nano-titanium dioxide damaged bacteria, causing cell walls to break at “relatively low concentrations,” similar to what you might see at a sewage treatment plant, Gruden says in an interview. But “in terms of function, what does that mean? Are the bugs able to do what they’re supposed to do?”

To answer that question, she added some biosolids to her test tubes and measured how much methane the bacteria produced as they digested for five days. The titanium dioxide didn’t seem to slow the bugs down; in fact, methane production actually increased. But when Gruden added nano-zinc oxide, gas production slowed down. She’s running more experiments this summer to see what happens when the bacteria are exposed to the bugs for a full 30 days.

“The take-home message for me is, the behavior of these particles is very complex,” Gruden says. “When you take a nanoparticle and put it into the environment, you have to know how it’s going to behave. And we don’t.”

Can you imagine what would happen if sewage treatment plants started failing? It’s not a nice picture. It’s the kind of risk that should make us slow down and stop pumping out more of these nanoparticles, at least until we know more about how they’ll behave in the environment.

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