SS3.17 Global Mercury Cycling: From Natural to Anthropogenic Sources
Date: Tuesday, June 11, 2002
Time: 2:45:00 PM
Location: Carson C
HinesME, University of Alaska Anchorage, Anchorage, USA,
Duddleston, K, N, University of Alaska Anchorage, Anchorage, USA, 
Hale, K, , University of Alaska Anchorage, Anchorage, USA, 
Bailey, E, A, USGS, Anchorage, USA, 
Faganeli, J, , Marine Biological Station, Piran, Slovenia, 
The degradation of methylmercury (MeHg) in nature appears to occur via two paths: 1) the organomercurial lyase enzyme (merB) catalyzes reductive demethylation and produces methane from MeHg; 2) oxidative demethylation results in carbon dioxide production or carbon dioxide plus methane during methanogenesis. To elucidate the relative importance of these paths, samples were incubated with 14C-MeHg, and rates of uptake and the relative production of 14C-carbon dioxide and 14C-methane determined. Anaerobic sediments primarily conducted oxidative demethylation. Sulfate-reducing marine sediments produced carbon dioxide from MeHg, whereas methanogenic freshwater sediments produced equal amounts of carbon dioxide and methane. In most instances, sediments from both environments exhibited a surficial maximum in methane production form MeHg that correlated with the extent that surficial regions were aerobic. Most soils produced only methane from MeHg, although some organic-rich or flooded soils yielded significant amounts of carbon dioxide. Freshwater sediments amended with nitrate or iron(III) produced carbon dioxide and methane, respectively. It appears that the mer system dominates under aerobic and iron-reducing conditions, whereas oxidative demethylation dominates during nitrate and sulfate reduction and methanogenesis.