Mercury Release to Aquatic Environments from Anthropogenic Sources in China from 2001 to 2012.

Based on an analysis of measured data and distribution factors, we developed the China Aquatic Mercury Release (CAMR) model, which we used to calculate an inventory of mercury (Hg) that was released to aquatic environments from primary anthropogenic sources in China. We estimated a total release of 98 tons of Hg in 2012, including coal-fired power plants (17%), nonferrous metal smelting (33%), coal mining and washing (25%), domestic sewage (17%), and other sectors (8.3%). The total primary anthropogenic Hg released to aquatic environments in China decreased at an annual average rate of 1.7% between 2001 and 2012, even though GDP grew at an annual average rate of 10% during this period. In addition to the Hg that was released to aquatic environments in China's provinces, we estimated the Hg release amounts and intensities (in g/km(2)·yr) for China's 58 secondary river basins. The highest aquatic Hg release intensities in China were associated with industrial wastewater on the North China Plain and domestic sewage in eastern China and southern China. We found that the overall uncertainty of our inventory ranges from -22% to 32%. We suggest that the inventory provided by this study can help establish a more accurate map of regional and global Hg cycling; it also has implications for water quality management in China.

Mercury Export from Mainland China to Adjacent Seas and Its Influence on the Marine Mercury Balance.

Exports from mainland China are a significant source of mercury (Hg) in the adjacent seas (Bohai Sea, Yellow Sea, East China Sea, and South China Sea) near China. A total of 240 ± 23 Mg was contributed in 2012 (30% from natural sources and 70% from anthropogenic sources), including Hg from rivers, industrial wastewater, domestic sewage, groundwater, nonpoint sources, and coastal erosion. Among the various sources, the Hg from rivers amounts to 160 ± 21 Mg and plays a dominant role. The Hg that is exported from mainland China increased from 1984 to 2013; the contributions from rivers, industrial wastewater, domestic sewage and groundwater increased, and the contributions from nonpoint sources and coastal erosion remained stable. A box model is constructed to simulate the mass balance of Hg in these seas and quantify the sources, sinks and Hg biogeochemical cycle in the seas. In total, 160 Mg of Hg was transported to the Pacific Ocean and other oceans from these seas through oceanic currents in 2012, which could have negative impacts on the marine ecosystem. A prediction of the changes in Hg exportation through 2030 shows that the impacts of terrestrial export might worsen without effective pollution reduction measures and that the Hg load in these seas will increase, especially in the seawater of the Bohai Sea, Yellow Sea, and East China Sea and in the sea margin sediments of the Bohai Sea and East China Sea.

Understanding the Evolution of Cobalt-Based Metal-Organic Frameworks in Electrocatalysis for the Oxygen Evolution Reaction.

Metal-organic frameworks (MOFs) have attracted increasing attention as a promising electrode material for the oxygen evolution reaction (OER). Comprehending catalytic mechanisms in the OER process is of key relevance for the design of efficient catalysts. In this study, two types of Co based MOF with different organic ligands (ZIF-67 and CoBDC; BDC=1,4-benzenedicarboxylate) are synthesized as OER electrocatalysts and their electrochemical behavior is studied in alkaline solution. Physical characterization indicates that ZIF-67, with tetrahedral Co sites, transforms into α-Co(OH)2 on electrochemical activation, which provides continuous active sites in the following oxidation, whereas CoBDC, with octahedral sites, evolves into ß-Co(OH)2 through hydrolysis, which is inert for the OER. Electrochemical characterization reveals that Co sites coordinated by nitrogen from imidazole ligands (Co-N coordination) are more inclined to electrochemical activation than Co-O sites. The successive exposure and accumulation of real active sites is responsible for the gradual increase in activity of ZIF-67 in OER. This work not only indicates that CoMOFs are promising OER electrocatalysts but also provides a reference system to understand how metal coordination in MOFs affects the OER process.

Evaluation of costs associated with atmospheric mercury emission reductions from coal combustion in China in 2010 and projections for 2020.

Coal combustion is the most significant anthropogenic mercury emission source in China. In 2013, China signed the Minamata Convention affirming that mercury emissions should be controlled more strictly. Therefore, an evaluation of the costs associated with atmospheric mercury emission reductions from China's coal combustion is essential. In this study, we estimated mercury abatement costs for coal combustion in China for 2010, based on a provincial technology-based mercury emission inventory. In addition, four scenarios were used to project abatement costs for 2020. Our results indicate that actual mercury emission related to coal combustion in 2010 was 300.8Mg, indicating a reduction amount of 174.7Mg. Under a policy-controlled scenario for 2020, approximately 49% of this mercury could be removed using air pollution control devices, making mercury emissions in 2020 equal to or lower than in 2010. The total abatement cost associated with mercury emissions in 2010 was 50.2×109 RMB. In contrast, the total abatement costs for 2020 under baseline versus policy-controlled scenarios, having high-energy and low-energy consumption, would be 32.0×109 versus 51.2×109, and 27.4×109 versus 43.9×109 RMB, respectively. The main expense is associated with flue gas desulfurization. The unit abatement cost of mercury emissions in 2010 was 288×103 RMB/(kgHg). The unit abatement costs projected for 2020 under a baseline, a policy-controlled, and an United Nations Environmental Programme scenario would be 143×103, 172×103 and 1066×103 RMB/(kgHg), respectively. These results are much lower than other international ones. However, the relative costs to China in terms of GPD are higher than in most developed countries. We calculated that abatement costs related to mercury emissions accounted for about 0.14% of the GDP of China in 2010, but would be between 0.03% and 0.06% in 2020. This decrease in abatement costs in terms of GDP suggests that various policy-controlled scenarios would be viable.

Mercury risk assessment combining internal and external exposure methods for a population living near a municipal solid waste incinerator.

Risk assessments for human health have been conducted for municipal solid waste incinerators (MSWIs) in many western countries, whereas only a few risk assessments have been performed for MSWIs in developing countries such as China where the use of waste incineration is increasing rapidly. To assess the mercury exposure risks of a population living near the largest MSWI in South China, we combined internal exposure and external exposure assessment with an individual-specific questionnaire. The mercury concentrations in air, soil, and locally collected food around the MSWI were assessed. The total mercury (T-Hg) and methylmercury (MeHg) of 447 blood samples from a control group, residential exposure group, and MSWI workers were measured. The internal and external exposures of the subject population were analyzed. Significant difference in MeHg concentrations was observed between the control group and the exposed group, between the control group and the MSWI workers, and between the exposed group and the MSWI workers (median levels: 0.70 µg/L, 0.81 µg/L, and 1.02 µg/L for the control group, exposed group, and MSWI workers, respectively). The MeHg/T-Hg ratio was 0.51 ± 0.19, 0.59 ± 0.17 and 0.58 ± 0.25, respectively. Multiple linear regression analysis indicated that MeHg concentrations were positively correlated with the gaseous mercury in the air. Combining internal and external exposure assessment showed that the direct contribution of MSWI emissions was minor compared with the dietary contribution. The external and internal exposures were well matched with each other. This study also suggested that an integrated method combining internal and external exposure assessment with an individual-specific questionnaire is feasible to assess the risks for a population living near a MSWI.