Even the cleanest environments in the world are contaminated by nanoparticles; these are the product, not of the nascent nanotechnology industry, but of natural processes. In the southern ocean between Cape Horn and the Antarctic, on the West Coast of Ireland, swept by Atlantic gales, significant numbers of particles in the 10nm – 100 nm size range can be detected. An interesting recent article in Nature (subscription required) provides an interesting analysis of natural nanoparticles from a sampling site in Ireland. These nanoparticles include, as you would expect, some made out of sea-salt. As is also already well-known, another major contribution to natural nanoparticles comes from sulfates, whose origin is probably the reduction of a chemical called DMS which is generated by plankton. This process has raised lots of interest because of its potential importance as a mechanism of climate control feedback as demanded by the Gaia hypothesis. The recent Nature paper adds a third class of materials to the mix – miscellaneous organic chemicals, that according to the season can comprise more than 60% of the mass of sub-micron particles. These, too, probably have their origin in the plankton near the sea’s surface.
Sampling sites closer to urban life predictably show greater concentrations of organic nanoparticles, arising from volatile organic compounds emitted from vehicle exhausts and other manmade sources. Even here, one surprise is the potential importance of gaseous hydrocarbons of natural origin – isoprene and terpenes – as contributors to the total VOC load. There’s a good brief discussion of the nanoparticle exposure that arises as a result of pollution in the Royal Society Report.
None of this diminishes the need to do good toxicological studies on new nanoparticles if there’s any danger of human or environmental exposure to them. But it does emphasise that a great deal is known about the behaviour of nanoparticles in the enivronment. The trouble is that the knowledge arises in a field – atmospheric chemistry – that seems at first to be far removed from the interests of nanotechnology. Nomenclature differences may seem trivial, but they actually take on a bigger significance in today’s world of computer searches. None of the literature on this subject would show up if you did a search on terms like “nanoparticles in the environment”; for these people nanoparticles aren’t “nanoparticles”, they’re “Aitken-mode aerosols”.