Our continuing work on the biogeochemistry of mercury is presently focused on the biochemical mechanism of Hg methylation. Since methylmercury is the species accumulated in fish via the food chain, this is a key transformation, but it has received surprisingly little attention over the past 20 years. We have discovered that, contrary to what is commonly believed, the acetyl-CoA pathway is not necessary for Hg methylation in sulfate-reducing bacteria. We are now checking if vitamin B12, which has been thought to be the key to mercury methylation, is necessarily involved. We are also conducting laboratory and field experiments to identify the sources of methylmercury in the ocean, since most people are exposed to mercury by seafood consumption.

In 2002, the Princeton atmospheric measurement site was installed on Fine Tower. Precipitation is being collected for methylmercury, total mercury and trace element analysis. Sources of methylmercury to the atmosphere will be identified by discerning source signatures in the trace element data and meteorologic transport analysis.