Asian Mercury Crossing the Ocean  | Mon May 4, 2009 6:18 PM EDT
A fascinating new study documents for the first time how mercury
gets from smokestacks in Asia to tuna on dinner tables in
America. Scientists sampled Pacific Ocean water from 16 sites
between Honolulu and Alaska, then constructed a computer model
linking atmospheric emissions, transport and deposition of
mercury, and ocean circulation.  Their findings published in
Global Biogeochemical Cycles show how mercury originating from
fossil-fuel-burning plants and waste-burning plants in Asia
falls into the Pacific Ocean near the Asian coastline. The
mercury-enriched waters are then carried by large ocean currents
east towards North America.  The study documents for the first
time something of the mysterious process by which mercury
becomes methylmercury in the ocean. The simple version: Mercury
rained down from the atmosphere is taken up by phytoplankton
living in sunlit waters. When these plankton die they rain down
into the depths where they're deco