Economic analysis of atmospheric mercury emission control for coal-fired power plants in China

Soil Geobacteraceae are the key predictors of neurotoxic methylmercury bioaccumulation in rice

Contamination of rice by the potent neurotoxin methylmercury (MeHg) originates from microbe-mediated Hg methylation in soils. However, the high diversity of Hg methylating microorganisms in soils hinders the prediction of MeHg formation and challenges the mitigation of MeHg bioaccumulation via regulating soil microbiomes. Here we explored the roles of various cropland microbial communities in MeHg formation in the potentials leading to MeHg accumulation in rice and reveal that Geobacteraceae are the key predictors of MeHg bioaccumulation in paddy soil systems. We characterized Hg methylating microorganisms from 67 cropland ecosystems across 3,600 latitudinal kilometres. The simulations of a rice-paddy biogeochemical model show that MeHg accumulation in rice is 1.3-1.7-fold more sensitive to changes in the relative abundance of Geobacteraceae compared to Hg input, which is recognized as the primary parameter in controlling MeHg exposure. These findings open up a window to predict MeHg formation and accumulation in human food webs, enabling more efficient mitigation of risks to human health through regulations of key soil microbiomes.

Looping Mercury Cycle in Global Environmental-Economic System Modeling

The Minamata Convention on Mercury calls for Hg control actions to protect the environment and human beings from the adverse impacts of Hg pollution. It aims at the entire life cycle of Hg. Existing studies on the Hg cycle in the global environmental-economic system have characterized the emission-to-impact pathway of Hg pollution. That is, Hg emissions/releases from the economic system can have adverse impacts on human health and ecosystems. However, current modeling of the Hg cycle is not fully looped. It ignores the feedback of Hg-related environmental impacts (including human health impacts and ecosystem impacts) to the economic system. This would impede the development of more comprehensive Hg control actions. By synthesizing recent information on Hg cycle modeling, this critical review found that Hg-related environmental impacts would have feedbacks to the economic system via the labor force and biodiversity loss. However, the interactions between Hg-related activities in the environmental and economic systems are not completely clear. The cascading effects of Hg-related environmental impacts to the economic system throughout global supply chains have not been revealed. Here, we emphasize the knowledge gaps and propose possible approaches for looping the Hg cycle in global environmental-economic system modeling. This progress is crucial for formulating more dynamic and flexible Hg control measures. It provides new perspectives for the implementation of the Minamata Convention on Mercury.

Emission control strategies of hazardous trace elements from coal-fired power plants in China

China's energy dependents on coal due to the abundance and low cost of coal. Coal provides a secure and stable energy source in China. Over-dependence on coal results in the emission of Hazardous Trace Elements (HTEs) including selenium (Se), mercury (Hg), lead (Pb), arsenic (As), etc., from Coal-Fired Power Plants (CFPPs), which are the major toxic air pollutants causing widespread concern. For this reason, it is essential to provide a succinct analysis of the main HTEs emission control techniques while concurrently identifying the research prospects framework and specifying future research directions. The study herein reviews various techniques applied in China for the selected HTEs emission control, including the technical, institutional, policy, and regulatory aspects. The specific areas covered in this study include health effects, future coal production and consumption, the current situation of HTEs in Chinese coal, the chemistry of selected HTEs, control techniques, policies, and action plans safeguarding the emission control. The review emphasizes the fact that China must establish and promote efficient and clean ways to utilize coal in order to realize sustainable development. The principal conclusion is that cleaning coal technologies and fuel substitution should be great potential HTEs control technologies in China. Future research should focus on the simultaneous removal of HTEs, PM, SOx, and NOx in the complex flue gas.

Appropriate scenarios for mercury emission control from coal-fired power plant in Thailand: emissions and ambient concentrations analysis

Optimum control of mercury released from the coal-fired power plant is evaluated by determining its efficiency and appropriateness in reducing emissions and ambient air concentrations. The 2400 MW power plant fueled by lignite located in Thailand is demonstrated in this study. Emissions of mercury from the coal-fired power plant are calculated under 3 major scenarios. The first scenario is the amount of mercury released under the existing operation of the power plant. Emission rate of mercury is calculated as 41 g/h which indicates a co-benefit of mercury removal from the installation of existing conventional air pollution treatment systems (electrostatic precipitator and wet flue gas desulfurization) as compare with the 2nd scenario of without equipping of air pollution control devices at the power plant (374 g/h of mercury emission). Adding controlling measures to existing operation of the power plant can lead to decreasing of mercury emissions at different levels. The relationship between changing of emissions affected to ambient air concentrations of mercury is evaluated using the CALPUFF air dispersion model. Results indicate small decreasing of predicted ambient concentrations after applying additional mercury control measures to the BAU of the power plant. This study reveals the co-benefit of existing air pollution treatment devices in controlling mercury emission. It also illustrates that the efficiency and appropriateness of current air pollution control system is in an optimal and acceptable levels in mercury control. Finding and methodology in this study can be used as a case study in quantitative evaluation of the effectiveness and appropriateness of environmental control mitigation measures added to the existing operations. It clearly illustrates the need to analyze the co-benefit of current air pollution control system towards the accomplishment on controlling emissions of other emerging air pollutants which will provide the best optimum air pollution control to the emission source.

A scoping study of component-specific toxicity of mercury in urban road dusts from three international locations

This scoping study presents an investigation of the total and bioaccessible mercury concentrations in road dust (RD) from three international urban sites, where a one-off sampling campaign was conducted at each. This was done to address the hypothesis that the matrix in which mercury is found influences its ability to become accessible to the body once inhaled. For that purpose, the samples were analysed for total and pulmonary bioaccessible mercury and the data compared to the chemical structure of individual particles by SEM. The results obtained from this study suggest that a high mercury content does not necessarily equate to high bioaccessibility, a phenomenon which could be ascribed to the chemical character of the individual particles. It was found that the Manchester samples contained more pulmonary soluble mercury species (as determined by elemental associations of Hg and Cl) in comparison to the other two samples, Curitiba, Brazil, and Johannesburg, South Africa. This finding ultimately underlines the necessity to conduct a site-specific in-depth analysis of RD, to determine the concentration, chemical structure and molecular speciation of the materials within the complex matrix of RD. Therefore, rather than simply assuming that higher bulk concentrations equate to more significant potential human health concerns, the leaching potential of the metal/element in its specific form (for example as a mineral) should be ascertained. The importance of individual particle behaviour in the determination of human health risk is therefore highlighted.

Methylmercury and inorganic mercury in Chinese commercial rice: Implications for overestimated human exposure and health risk

China is the largest rice producer and consumer in the world, and mercury (Hg) levels, particularly methylmercury (MeHg), in rice and health exposure risks are public concerns. Total Hg (THg) and MeHg levels in 767 (domestic = 709 and abroad = 58) Chinese commercial rice were investigated to evaluate Hg pollution level, dietary exposures and risks of IHg and MeHg. The mean rice THg and MeHg levels were 3.97 ± 2.33 μg/kg and 1.37 ± 1.18 μg/kg, respectively. The highest daily intake of MeHg and IHg were obtained in younger groups, accounted for 6% of the reference dose-0.1 μg/kg bw/day for MeHg, 0.3% of the provisional tolerance week intake-0.571 μg/kg bw/day for IHg. Residents in Central China and Southern China meet the highest rice Hg exposure, which were more than 7 times of those in Northwest China. Lower concentrations than earlier studies were observed along the implementations of strict policies since 2007. This may indicate that a declining temporal trend of Hg in Chinese grown rice and associated exposures could be obtained with the implementations of strict policies. Though there exist Hg pollution in commercial rice, Hg levels in Chinese commercial rice is generally safe compared with Hg polluted sites. Populations dwelling in China have relatively a quite low and safe MeHg and IHg exposure via the intake of commercial rice. Strict policies contributed to the decrease in THg and MeHg levels in Chinese-grown rice. More attention should be paid to younger groups.

Pollution characteristics and source difference of gaseous elemental mercury between haze and non-haze days in winter

The distribution characteristics and sources of gaseous elemental mercury (GEM) on haze and non-haze days are still not clear. During the winter heating period in 2017, the GEM concentrations in Qingdao were studied for their differences, sources, and pollution characteristics on haze and non-haze days. The GEM concentration on haze days (2.81 ± 2.23 ng/m³) was higher than that on non-haze days (1.90 ± 1.21 ng/m³) and the difference was significant (p < 0.01) during the period of artificial heating. The average concentration of GEM was 2.27 ng/m³ in the heating period, but lower than that before heating (3.30 ng/m³). However, the mercury to carbon monoxide ratio (GEM/CO) on haze days was lower than that on non-haze days. The ratio of GEM/CO in this study was lower than that in other studies reported from China. There was a positive correlation between the GEM/CO ratio and the air temperature (p < 0.01), suggesting that the mercury released from the Earth's surface was important. The environmental policies of China also contributed to decrease of the GEM/CO ratio. Similar diurnal patterns appeared on both haze and non-haze days, with one GEM peak at 14:00-15:00. This pattern was different from the bimodal pattern of other atmospheric pollutants in the morning and evening rush hours and was controlled by GEM from the Earth's surface (mostly re-emission of legacy Hg) whether on haze or non-haze days. Principal component analysis showed that the contribution of GEM directly from anthropogenic sources was relatively small. The main influencing factor on haze days was air temperature. GEM concentrations showed large spatial differences in air masses from different places. The GEM concentration in air masses from southern and the western Shandong Province was higher than from the north on haze days.

Occupational exposure to respirable dust from the coal-fired power generation process: sources, concentration, and health risk assessment

To investigate the contamination levels of respirable dust released in the work environment and the induced workers' health risk at a coal-fired power plant, we collected 405 dust samples from different dusty workstations by personal sampling during the coal-fired power generation process. Then, an inhalation risk assessment model from the USEPA was combined with the Monte Carlo simulation method to quantitatively evaluate the health risk caused by dust inhalation. Of 10 workstations researched, the dust concentration in the most workstations exceeded the prescribed occupational exposure limit. Workers engaged in ash removal suffered the highest health risk at 4.08 × 10^-6 ± 2.85 × 10^-6 (95% CI), closely followed by those involved in other job categories. The results can contribute to the formulation of targeted dust prevention measures and implementation of risk management for the coal-fired power sector.

Control of mercury emissions from stationary coal combustion sources in China: Current status and recommendations

Coal burning in power plants and industrial boilers is the largest combustion source of mercury emissions in China. Together, power plants and industrial boilers emit around 250 tonnes of mercury each year, or around half of atmospheric mercury emissions from anthropogenic sources in the country. Power plants in China are generally equipped with multi-pollutant control technologies, which offer the co-benefit of mercury removal, while mercury-specific control technologies have been installed in some facilities. In contrast, most industrial boilers have only basic or no flue gas cleaning. A combination of measures, including energy conservation, coal switching and blending, reducing the mercury contents of coals through washing, combustion controls, and flue gas cleaning, can be used to reduce mercury emissions from these stationary combustion sources. More stringent emission standards for the major air pollutants from coal-fired power plants and industrial boiler, along with standards for the previously unregulated mercury, were implemented recently, which is expected to bring significant reduction in their mercury emissions through the necessary upgrades of multi-pollutant and mercury-specific control technologies. Meanwhile, strong monitoring capacity and strict enforcement are necessary to ensure that the combustion sources operate in compliance with the new emission standards and achieve significant reduction in the emissions of mercury and other air pollutants.

Chemical forms of the fluorine, chlorine, oxygen and carbon in coal fly ash and their correlations with mercury retention

Fly ashes recovered from the particulate control devices at six pulverized coal boiler unites of China, are studied using an X-ray photoelectron spectroscopy (XPS) with a particular focus on the functionalities of fluorine (F), chlorine (Cl), carbon and oxygen on fly ash. It is found that the inorganic forms of F and Cl are predominant on the ash surface in comparison with their organics, and the proportion of organic Cl is relatively higher than that of organic F. Similar results are also obtained in the bulk by correlating the F and Cl contents with those of the unburnt carbon and other compositions in ash. Strong correlations of mercury retention with surface carbon-oxygen functional groups indicate that the C=O, OH/C-O and (O-C=O)-O on surface are of significant importance for mercury retention in fly ash. Their surface concentrations are related to coal type. The presence of Cl in fly ash helps with mercury retention. No obvious effect of F is observed.

Effect of HBr formation on mercury oxidation via CaBr2 addition to coal during combustion

Adding CaBr₂ to coal to enhance elemental mercury (Hg⁰) oxidation during combustion has been an effective mercury control technology, but the added CaBr₂ may increase levels of noxious Br₂ or HBr gases in flue gas.