Rotorua is looking forward to a boost in the number of tourists following the publication of a recent study showing that hydrogen sulfide, the "rotten egg" gas that pervades the city, is possibly linked to erectile function. As a chemist, I won't get into the biological side of things, but this does give me a nice excuse to write about this rather interesting molecule.
Hydrogen sulfide has the chemical formula H2S, and its molecules comprise a sulfur atom flanked by two hydrogen atoms in a bent arrangement. Its structure is in fact very similar to that of water (H2O), but that's where the similarities end.
Whereas water is a harmless, odourless liquid at room temperature, hydrogen sulfide exists under these conditions as a gas which is both extremely poisonous and extremely smelly.
I am sure that most of you are familiar with the smell, but not perhaps with the incredible intensity of the smell - hydrogen sulfide can be detected by the human nose at concentrations around 0.02 parts per million; this is roughly the equivalent of tasting a tablespoon of sugar in a volume of water the size of Moana Pool.
If we are exposed to low concentrations of hydrogen sulfide for long periods of time, our nose gets fatigued and we can no longer smell its characteristic odour - given the fact that hydrogen sulfide is of comparable toxicity to hydrocyanic acid (HCN), the gas that was used in gas chambers in the US, this is, I'm sure you'll agree, not a good thing.
Indeed, there have been six fatalities in Rotorua due to inadvertent inhalation of hydrogen sulfide since 1987, the most recent being in 2008. Deaths have occurred worldwide in workplaces such as oil refineries, sewers and fishing boats, where concentrations of hydrogen sulfide can quickly build to fatal levels.
A number of deaths have also been reported on farms as a result of exposure to liquid manure, again arising from the high concentration of the gas.
So it comes as some surprise to find this highly toxic molecule might very well be important in a rather fundamental biological process. In fact, hydrogen sulfide is present in the blood in very low concentrations, deriving from breakdown of an amino acid called cysteine.
A study reported last year showed that mice having relatively low levels of hydrogen sulfide in their blood had higher blood pressures than those with more normal levels, thus raising the possibility that hydrogen sulfide may also play an important role in regulating blood pressure.
It will be interesting to see where these results lead. Will Rotorua become the worldwide Mecca for honeymooning couples? The Vacationers Viagra? Or, in the fullness of time will we find that this has simply been blown up out of all proportion?
- Dr Blackman is an associate professor in the chemistry department at the University of Otago.
