Do volcanoes emit mercury? Understanding the behaviour of Hg in volcanic products.

This is a proposal to make some modern measurements of the quantities of volatile trace metals that are released to the atmosphere by volcanoes. Volcanic gases are often equated with sulphur. In fact, sulphur is just one component of volcanic gases; and in just the same way that sulphur from volcanoes can affect the atmosphere, so may other species. We wish to make measurements of mercury at volcanoes. Mercury is a curious element: in its elemental form (Hg(o)) it is very volatile, and is not usually very reactive. As a result, once it is in the atmosphere it will stay there for a long time (about a year), before eventually being removed. Mercury is of general interest because it is highly toxic [the cause, for example, of the condition described by the phrase 'mad as a hatter']. It has no 'useful' function for biological organisms, but becomes concentrated up the food chain. One of the big problems with the current understanding of natural mercury in the atmosphere is that the books don't balance: we don't know very well where mercury is released from; and we don't know where it ends up. It is possible that volcanoes contribute to this imbalance: some people think that volcanoes may release a large amount of mercury, perhaps as much as half of all natural emissions; others think that it is so small that it can be ignored. By making measurements close to the vent of two active volcanoes using some new and very sensitive equipment, we hope to resolve this problem: at the very least, we'll know how much mercury is released by steady, gentle activity at the world's persistently active volcanoes. These volcanoes might not hit the headlines, but our idea is that they are always there in the background, supplying gases and particles to the atmosphere. A second scientific problem that we want to look at is to understand how mercury escapes from molten lavas; in what forms it escapes (is it mainly in the gaseous form? or does some of it very quickly form very small particles? and if so , what happens to those particles?); and we want to use the way that mercury behaves to understand more about the extreme (hot, oxidising, chemically reactive) environment that is a volcanic plume. A third aspect that we also wish to study is to use the erupted rocks and minerals (at the same two volcanoes, Etna and Kilauea) to try and understand how mercury and its chemically-similar 'cousins' (metals including Cd, Zn, Cu) behave as a rock cools and crystallises. We think that mercury and cadmium, for example, should have a slight preference for certain minerals (clinopyroxene, feldspar), and that as a result their concentration in the melt won't change much during crystallisation, but may change a little by 'degassing'. We can test this idea using precise (laser) measurements of small samples of real rocks.