Search

Foliage uptake of atmospheric elemental mercury (Hg0) and subsequent translocation by the phloem is the main pathway for Hg accumulation in tree rings. Tree rings have been used as the emerging natural archive to directly reconstruct centennial trends of atmospheric Hg0 level. The tree-ring Hg records in remote regions have successfully reconstructed the peak of anthropogenic Hg emissions in Europe and North America in 1960s − 1970s and the distinct increase of Hg emissions in Asia since 1980s. Combining the Hg concentrations and isotopic signatures would provide historical atmospheric Hg trends and Hg emission source shifts. The mechanisms for Hg translocation, specifically the radial translocation and impacts of environmental and tree physiological factors, are yet to be clarified to explain the nonlinear relation between atmospheric Hg0 concentration and Hg signals in tree rings. Thus, we recommend to trace Hg accumulation and translocation processes and their Hg isotopic fractionation in tree rings, and examine the relationship between tree-ring Hg profile and atmospheric pollution level in specific tree species. Finally, we suggest to develop more statistical models to quantify environmental and tree physiological impacts on Hg accumulation and translocation in tree rings. [ABSTRACT FROM AUTHOR]

Although mercury (Hg) is toxic at all valence states, organic Hg, especially monomethylmercury (MeHg, CH3Hg+, methylmercury), is more toxic than inorganic Hg (Hg(II), Hg2+). As Hg is predominately methylated via bio-methylation, studies on the mechanism of Hg bio-methylation by microorganisms are particularly important. It is widely accepted that MeHg is mainly produced by anaerobic microorganisms in the environment, and the Hg-methylating process is a cellular reaction. Hence, the production rate of MeHg is not only related to the presence and activities of Hg-methylating anaerobic microorganisms, but also the transport of Hg(II) into microbial cells and the biochemical reactions for forming MeHg in the cells. Therefore, this review described the current state of knowledge on: 1) what kind of microorganisms can methylate Hg; 2) what pathways are the Hg(II) take to enter into the microbial cells; 3) what kind of biochemical reactions happen in the cells; and 4) biogeochemical factors affecting Hg methylation, which are critical to elucidate the regulating mechanisms of Hg methylation by microorganisms. Simultaneously, the existing issues or controversies on biotic Hg methylation were also discussed. [ABSTRACT FROM AUTHOR]

Two new compounds, myrubol (1) and 3-oxo-11α-hydroxyfriedelane (2), were isolated from the roots of Myrica rubra along with eight known compounds (3-10). Their structures were determined through 1H-NMR and 13C-NMR spectral data, including 2-D experiments (HMBC, HMQC, 1H-1H COSY and NOESY) and high-resolution mass spectrometry. [ABSTRACT FROM AUTHOR]