Mercury in vegetation and soils at abandoned mercury mines in southwestern Alaska, USA

Abstract

We chemically analysed vegetation (willow and alder) and soil samples collected at three abandoned mercury (Hg) mines and at background sites in southwestern Alaska and compared Hg concentrations, speciation and distribution. Total Hg and methylmercury (MeHg) concentrations were higher in vegetation and soil samples from all the mine sites compared to samples from the background sites, but there was no correlation between total-Hg concentrations in vegetation and total-Hg concentrations in soil or between total-Hg and MeHg concentrations. However, the percent MeHg of the total Hg was higher in samples from the background sites compared to samples from the mine sites and is higher in vegetation samples than in corresponding soil samples. The percent MeHg is an order of magnitude higher in the willow samples than in corresponding alder or soil samples. The percent of divalent Hg [Hg(II)] is highest in soil samples from the retort and background areas. The higher percent MeHg in vegetation and soil in samples from background sites may be explained by the higher proportions of reactive Hg species, such as Hg(II), at these sites compared to the surface mined and tailings areas where most of the Hg is in the elemental and cinnabar (HgS) forms. Dissolved gaseous Hg species are more readily accumulated in vegetation and are more readily methylated than solid phases like HgS and liquid Hg.

Distribution and speciation of mercury in soil in the area of an ancient mercury ore roasting site, Frbejžene trate (Idrija area, Slovenia)

“…Compared to the established Hg median (3.2 mg/kg) and maximum (75 mg/kg) values for soils for the area in the surroundings of Idrija town , the Hg median in soils of the Frbejžene trate area were about 100-fold higher and the maximum value was almost 300-fold higher. Total Hg concentrations in the soils and SOM from the investigated area were comparable to Hg contents determined in calcines from the Almadenejos site in Spain (34,000 mg/kg; Gray et al, 2004), in soils from Hg mines in south-western Alaska (46,000 mg/kg; Bailey et al, 2002) and in soil from the Mieres mining site in northern Spain (29,304 mg/kg;Fernandéz-Martinez et al, 2006). Regarding these reported Hg values in soils and mine waste from different Hg mining areas, it is evident that Hg contents determined at the ancient roasting site Frbejžene trate are among the highest ever reported, despite the fact that about 400 years have passed since ore processing ceased at this site.…”

Mercury Speciation and Microbial Transformations in Mine Wastes, Stream Sediments, and Surface Waters at the Almadén Mining District, Spain

“…Highly elevated Hg concentrations in mine wastes from other Hg mines worldwide are common, but total Hg concentrations in mine-waste calcines from the Almadén District are among the highest previously reported ( Table 1). Only soils collected from Hg mines in southwestern Alaska (22) have been reported to contain higher Hg concentrations (46 000 µg/g).…”

Mine Wastes

“…The presence of organic acids in vegetated mine wastes promotes the release and colloidal transport of mercury from such wastes. Furthermore, mercury is transformed by bacteria into organic forms, notably monomethyl mercury (CH 3 Hg + ) and dimethyl mercury ((CH 3 ) 2 Hg) (Bailey et al 2002;Gray et al 2002bGray et al , 2004Gray et al , 2006Li et al 2008a). Furthermore, mercury is transformed by bacteria into organic forms, notably monomethyl mercury (CH 3 Hg + ) and dimethyl mercury ((CH 3 ) 2 Hg) (Bailey et al 2002;Gray et al 2002bGray et al , 2004Gray et al , 2006Li et al 2008a).…”