A Smell of Osmium in the Air
A couple of months ago, I had to struggle very hard in order to be allowed to use osmium tetroxide for my experiments. Safety rules enforced at my institute make it almost impossible to obtain this apparently super toxic compound… so my curiosity was excited when I found a paper in PNAS (also commented on Scientific American) saying the earth surface is actually being slowly covered by a thin layer of osmium, very likely to be released by human activities.
Osmium (named after the greek ‘osme’, meaning smell) is a trace element found in sea water and earth crust, particularly in platinum ores. It is usually mentioned in undergrad teaching for being the heaviest element with a density of 22600 kg/m3 or because its above-mentioned derivative, osmium tetroxide, is extremely toxic (it is also a smelly compound, hence the metal’s name).
A team led by Mukul Sharma at Dartmouth College investigated the osmium-187 vs osmium-188 ratios in various locations on earth. In deep seawater (samples were collected 2000m deep in Atlantic ocean) this ratio is roughly equal to 1, whereas in platinum ores, there is usually 5 times more Os-188 than Os-187. Remarkably, samples obtained from surface seawater or rain showed an intermediate ratio, i.e. enriched in Os-188 compared to deep seawater. It is then very likely that extracted osmium (i.e. with an increased amount of Os-188) from (mainly) platinum ores is slowly dissipated into the atmosphere. Platinum is indeed widely used for the production of automobile catalytic converters. Refinement processes of platinum after mining occur at very high temperatures (~1000°C), and osmium traces can be converted into very volatile osmium tetroxide. In the absence of appropriate exhaust gases scrubbing systems, osmium is then released in the atmosphere. This, the authors say, is not directly endangering us since the involved quantities are far too small, but it provides us with another hint on how industrial processes are able to modify our ecosystems, sometimes in unexpected ways!
Ref:
C. Chen et al., Proc. Natl. Acad. Sci. USA 2009, 106, 7724. doi: 10.1073/pnas.0811803106
There are Os-hydrotalcite solid catalysts that work quite well in osmium-type oxidations as well. Kind of obscure, but interesting. It involves a bit of modest calcining.
you could have ordered sodium osmate instead, from Aldrich, there are probably no restrictions on it