Don’t Worry about the Nanotubes

I was feeling a little anxious about nanotech recently. I couldn’t put my finger on it, but something just wasn’t quite right. Then, within a few days, half a dozen people warned me about a new paper to be published in Nature by eminent UK toxicologist Ken Donaldson about the toxicity of carbon nanotubes. Ah, that was it—a lack of nanotech scare stories for a while, so something had to be done.

The various nanotech trade organizations were already swinging into action and preparing their responses to a hostile press, and the scientific community was all a twitter. From the point of view of the Nanotech Industries Association, European Nanotechnology Trade Alliance and Nanobusiness Alliance, this was something that could damage the nascent nanotech industry.

Well, the nanotech industry has been nascent for the last 10 years, which makes the gestation time of the biotech industry or the blue whale look positively sprightly. I often wonder whether these people will ever realize there’s no nanotech industry.

Perhaps if we told them that repeatedly banging their heads against the wall would make them rich, they could spend the next 10 years doing that. I wouldn’t want to live next door, but it would make life simpler for the rest of us actually working in nanotech if a bunch of people with no knowledge about the subject would stop attempting to defend us from things about which we’re not concerned.

So what was this dramatic finding? Simply that long carbon nanotubes can cause lung damage similar to asbestos, whereas shorter ones do not, and this highlights a problem that has little to do with nanotubes but a lot to do with the safety of nanomaterials in general.

As a species, we’ve gotten pretty good at defending ourselves from attack. Anything attempting to sneak into our body via the stomach gets a bath in strong acid, and anything else will soon find itself under attack from that most ferocious of predators, the macrophage.

A macrophage (from the Greek words for big eater) has the job of cleaning up any rubbish that gets into our systems, from bacteria to dust. It does this by engulfing the invader and then, in the case of a virus, calling up T-cells to produce antibodies or just simply removing the foreign matter from circulation.

Donaldson’s study looked at the ability of alveolar macrophages, the ones specific to the lungs, to engulf various forms of nanotubes, a process known as phagocytosis. When an alveolar macrophage engulfs a dust particle, it’s relatively happy, but long, thin materials, especially insoluble ones such as nanotubes that can’t be partially dissolved to make them flexible, require a trick more akin to sword swallowing.

Although alveolar macrophages look like amorphous blobs, they can stretch to engulf larger particles but only within limits. Once these particles get to more than 20 microns in length, the macrophage just can’t stretch far enough to engulf the particle, something known as frustrated phagocytosis; it’s the equivalent to a 6-foot-tall sword swallower attempting to swallow a 7-foot sword--or in my case, attempting last week to eat dessert, the seventh course, in a Michelin-starred restaurant in France. Just like a macrophage, I ended up with severe indigestion.

But there’s a certain amount of ‘so what’ associated with this type of report. Just as I know from experience that over indulging on foie gras has serious consequences, we also know that getting long, thin, insoluble fibers into your lungs causes problems, and that’s just what asbestosis is.

The main problem is that thin, insoluble fibers aren’t something we’ve encountered in nature over the last 50,000 years; otherwise, we’d have evolved a way of dealing with them or become extinct. Smaller particles are easily dealt with because we encounter these all the time—from ocean spray containing salt nanoparticles to combustion products of everything from camp fires to automobile engines—so there’s less to worry about there. However, we do have a solution, but this time because of human ingenuity rather than biological evolution.

I first encountered the problem of frustrated phagocytosis almost eight years ago as a result of looking at carbon nanotubes. The reason the subject was raised was that it was known to be a cause of asbestosis, and we were wondering whether carbon nanotubes could cause the same problems. Eight years later, and after nearly five years of research, Ken Donaldson’s group has confirmed that nanotubes could cause similar effects, but we don’t really have to worry about waiting for toxicology results.

In the case of asbestos, it was found to have some quite remarkable properties, so we went around making insulation with it for everything from building materials to boilers. It was only later, when we began to see the health effects of asbestos, that we realized it might be a problem.

That’s very last century—use stuff, make stuff, sell stuff and worry about the damage later. In the 21st century, there’s been a major shift. We now have sophisticated instrumentation and sufficient experience in toxicology to pop something in a microscope and say, “Hmm, I wonder if that could behave like asbestos.” Ten years later, the toxicologists will catch up, but in the meantime, everyone has been very cautious about exposure to carbon nanotubes.

Overall, I think everyone is being very responsible about the use of nanotubes and other nanomaterials, and in what may be disappointing to any lawyers reading, I don’t think we’ll see class-action suits on the scale of asbestos or tobacco. Even the publication of Donaldson’s paper in Nature didn’t create the killer nanotech headlines for which some were hoping, not least in the burgeoning nanotoxicology industry.

So we can all relax and get on with improving the quality of life and saving the planet with our safe, harmonious, 21st century nanotechnologies. As Franklin D. Roosevelt famously said, “The only thing we have to fear is fear itself.” That applies more to the various trade associations than anyone else working with nanomaterials.

Perhaps more appropriate would be another FDR quote: “The only limit to our realization of tomorrow will be our doubts of today.”

Tim Harper, PhD, is contributing editor to The Real Nanotech Investor and president and founder of the international nanotech consultancy Cientifica.