| dc.description.abstract | While mercury (Hg) is a well-known neurotoxic element, it is still being used for or incorporated into certain industrial processes and commercial products as a result of its unique physicochemical properties, which leads to a situation that some of these Hg-bearing solid wastes may eventually be disposed in conventional landfills, especially in places where systematic recycling practices are difficult to implement. The presence of Hg in landfills is a concern due to the potential for it to volatilize or leach from the landfill site and impact local ecosystems. However, earlier studies were merely focused on documenting the emissions of Hg as landfill gas. Little has been undertaken to investigate the possible release of Hg in leachate, as well as the biogeochemical processes that control Hg transformations in landfills. Given that the genomic information derived from a recently identified gene cluster (i.e., hgcAB) encoding for proteins essential for microbial Hg methylation has indicated that the anaerobic conditions in landfills can foster the growth of some fermentative bacteria, syntrophs and methanogens that were previously unrecognized but now are acknowledged as Hg-methylators, it is important to re-examine the speciation and in particular methylation potential of Hg within the landfill environment. Accordingly, in this study three landfills designated as A, B and C in northern Taiwan were chosen as the research sites to obtain leachate samples. Specific emphases were placed on characterization of geochemical conditions and determination of Hg bioavailability and transformations including reduction, methylation and demethylation in these settings. Preliminary results show that, as expected, concentrations of total Hg measured in the leachate samples (69-246 pM) lie within the range reported for the background environmental Hg level, presumably due to both the thorough and consistent implementation of recycle/reuse policy in Taiwan and a prolonged period of landfill termination. Levels of analyzed geochemical parameters such as 1000 mg/L COD, 200 mg/L TOC, 0.2 mg/L DO, as well as 20 – 200 mV ORP also support the observation that the landfill maturation of the study sties has reached at or beyond the stage of Phase IV. Further, microcosm experiments conducted with spike of inorganic Hg(II), methylmercury and Geobacter sulfurreducens PGA (i.e., a model Hg-methylating bacterium) into leachates in the presence or absence of bacterial growth inhibitors reveal that at this stage, the potential for in situ Hg methylation seems to be limited owing to poor bioavailability of inorganic Hg and vigorous biotic demethylation of organomercury. Together, not only can these results be used as the baseline data for future comparisons, but they also indicate that the impact of Hg contamination from the three studied landfill sites on the surrounding environment is likely trivial. Nonetheless, considering the fact that the chemical and microbiological conditions vary in different phases of the landfill maturation process, future study on the relative importance of these conditions in governing mercury transformations in prior phases, particularly Phases II & III, is warranted. | en_US |