Mercury speciation in wet deposition samples collected from a coastal area of Minamata Bay: Fid-Bau Portal

Mercury speciation in wet deposition samples collected from a coastal area of Minamata Bay

Marumoto, Kohji / Matsuyama, Akito

Abstract To better understand the methylation and demethylation of mercury (Hg) in the atmosphere, monomethyl mercury (MMHg) concentrations in wet deposition samples collected in the Minamata Bay area from September, 2009 to August, 2010 were determined. The concentrations of total Hg (dissolved Hg + particulate Hg) and dissolved reactive Hg were also measured. The volume-weighted mean concentrations of dissolved MMHg and total Hg were 0.061 and 5.9 ng L⁻¹, respectively. Almost 90% of total Hg was in the dissolved phase and dissolved reactive Hg was the dominant Hg species in the wet deposition. The wet deposition fluxes of total Hg and reactive Hg increased in the rainy season (summer and fall), while the concentrations and wet deposition fluxes of MMHg were higher in winter and spring than in summer. Factors affecting this seasonal variation of MMHg were also considered. The MMHg in wet depositions may be decomposed by the increased levels of UV radiation in summer months, although MMHg can also be emitted from anthropogenic and biogenic sources and/or produced by photochemical reactions. Long-range transport from the Asian continent may also contribute to the seasonal variation of the wet MMHg deposition flux.

Highlights • Our study provides the first data of wet depositions of monomethyl mercury (MMHg) in Japan. • Both concentrations and depositions of MMHg are higher in winter and spring than in summer. • Our data indicate MMHg in wet depositions can be decomposed by strong UV-A in summer. • Long-range transport of air masses from the Asian Continent may contribute to enhanced MMHg in rainwater in winter and spring.