When Nanoparticles Wash Away

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 nanometalsâtitanium dioxide and zinc oxide, used in sunscreens, paint and other productsâon bacteria.

Metals âcan be toxic to microorganisms,â she notes. âIn fact, thatâs specifically what theyâre forâ 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 whatâs delicately known in the business as âbiosolids.â

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 ârelatively low concentrations,â similar to what you might see at a sewage treatment plant, Gruden says in an interview. But âin terms of function, what does that mean? Are the bugs able to do what theyâre supposed to do?â

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 didnât seem to slow the bugs down; in fact, methane production actually increased. But when Gruden added nano-zinc oxide, gas production slowed down. Sheâs running more experiments this summer to see what happens when the bacteria are exposed to the bugs for a full 30 days.

âThe take-home message for me is, the behavior of these particles is very complex,â Gruden says. âWhen you take a nanoparticle and put it into the environment, you have to know how itâs going to behave. And we donât.â

Can you imagine what would happen if sewage treatment plants started failing? Itâs not a nice picture. Itâs 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 theyâll behave in the environment.