10 Dec 2014 Bad Nano-tox
When I once had to give a conference talk on nano-safety I started off by saying; "Ladies and gentlemen. I am now going to start my talk by unleashing billions of provably toxic nanoparticles into the audience."
My assistant then entered the hall carrying a candle. When she reached the front and handed it over to me I blew it out. For the first time the audience could see some smoke. "Don't worry about that - particles big enough to see are no longer nano and nowhere near as harmful."
When Dr Nigel Holmes and I wrote our book Nanocoatings: Principles and Practice we tried to put nanosafety into context. Although there are plenty of unknown unknowns, that's part of the day job in everything we do in safety and nanosafety is nothing more than a sensible assessment of the risks - no different from anything else we do. "Nano" merely means "small" and means neither "evil" nor "amazing so give us money to fund our work".
Our private opinion, which we dared not express in writing, was that much of nano-toxicology was very bad research done merely by people who jumped on a funding bandwagon itself propelled by some hysteria about nano going to destroy us all. But even non-experts such as ourselves could work out that levels of natural nanoparticles were often orders of magnitude higher than anything man-made. Some of them (e.g. erionite naturally found in Turkey) are as bad as asbestos. And the nanoparticles from candles are at provably higher levels in Danish homes (Danes especially love candles) than in busy city streets. This doesn't mean we can be casual about the safety of nanoparticles; simply use straightforward toxicity principles based on intrinsic harmfulness and exposure dose.
The blockbuster review by Prof Harald Krug in Angewandte Chemie (an Open Access link) of ~10,000 nano-tox studies is truly shocking. Most of the work is worthless and/or wrong. As he points out, people without even elementary toxicology training have received funding to do work which provides absolutely no useful guidance on the real risks of the nanoparticles they were studying. There's no need for me to try to summarize - just click on the link and read it for yourself. Sometimes such reviews hide their dismay behind academic niceties. Prof Krug has no time for such niceties.
Incidentally, it is well known that there have been large numbers of deaths caused by candles. I happen not to know how many were caused by their nanoparticles, but I'd be prepared to bet that vast majority of the deaths arose from the fires accidentally started by the candles.