China's retrofitting measures in coal-fired power plants bring significant mercury-related health benefits

Abstract

•CFPP retrofitting measures in China avoided 114 Hg-related deaths during 2011–2015•CFPP shutdowns made the largest contribution to Hg-related health benefits•Hg mitigation produces significant transregional health benefits•Health impact assessment should be incorporated into Hg mitigation policies A total of 128 countries, including China, ratified the legally binding Minamata Convention in 2017 to mitigate highly toxic mercury (Hg), primarily targeting coal-fired power plants (CFPPs). China committed to reducing Hg emissions via various retrofitting measures in CFPPs, including the closure of small unit CFPPs, installation of efficient air pollution control devices, and power generation efficiency improvement. However, the effectiveness of these measures on Hg emissions and the related health effects remain poorly understood. In this study we found that Hg emissions have been reduced by 23.51 tons during 2011–2015, which prevented 114 deaths and 30,484.77 points of IQ decrement. Hg mitigation also produces significant mutual health benefits across regions. However, more stringent and effective Hg control measures are urgently needed, and various factors, including CFPP location, population density, and trade-offs between reductions in total Hg and in Hg2+, must be carefully considered. China has implemented retrofitting measures in coal-fired power plants (CFPPs) to reduce air pollution through small unit shutdown, the installation of air pollution control devices (APCDs), and power generation efficiency improvement. The reductions in highly toxic Hg emissions and their related health impacts by these measures remain poorly understood. Here, we evaluated the health benefits of reduced Hg emissions via retrofitting measures during China's 12th Five-Year Plan (2011–2015) by combining plant-level Hg emission inventories with the China Hg Risk-Source-Tracking Model. We found that the measures reduced Hg emissions by 23.5 tons (approximately 1/5 of that from CFPPs in 2010), preventing 30,484.77 total points of intelligence quotient decrement and 114 deaths between 2011 and 2015. These benefits were dominated by CFPP shutdowns and APCD installations, and nearly 50% of provincial health benefits were attributable to Hg reductions in other regions. We suggest that Hg control strategies should consider various factors, such as CFPP location, population density, and trade-offs between reductions in total Hg and in Hg2+. China has implemented retrofitting measures in coal-fired power plants (CFPPs) to reduce air pollution through small unit shutdown, the installation of air pollution control devices (APCDs), and power generation efficiency improvement. The reductions in highly toxic Hg emissions and their related health impacts by these measures remain poorly understood. Here, we evaluated the health benefits of reduced Hg emissions via retrofitting measures during China's 12th Five-Year Plan (2011–2015) by combining plant-level Hg emission inventories with the China Hg Risk-Source-Tracking Model. We found that the measures reduced Hg emissions by 23.5 tons (approximately 1/5 of that from CFPPs in 2010), preventing 30,484.77 total points of intelligence quotient decrement and 114 deaths between 2011 and 2015. These benefits were dominated by CFPP shutdowns and APCD installations, and nearly 50% of provincial health benefits were attributable to Hg reductions in other regions. We suggest that Hg control strategies should consider various factors, such as CFPP location, population density, and trade-offs between reductions in total Hg and in Hg2+. Mercury (Hg) is a globally recognized contaminant posing great risks to both humankind and ecosystems.1Giang, A.; Selin, N.E., Benefits of mercury controls for the United States. Proc. Natl. Acad. Sci. 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CFPPs are one of the largest anthropogenic sources of global atmospheric Hg emissions, and have been listed as a key sector for Hg emission reduction in the Minamata Convention. According to the latest Global Mercury Assessment 2018, the contribution of CFPPs to global anthropogenic Hg emissions decreased from 16% in 2010 to 14% in 2015, but the Hg emissions from CFPPs in East and Southeast Asia witnessed a growth of 19.2% during 2010–15.2United Nations Environment Programme Global mercury assessment 2018; Switzerland.https://www.unenvironment.org/resources/publication/global-mercury-assessment-2018Date: 2019Google Scholar China, as the world's largest coal-fired power generator, emitted 73 tons of Hg from CFPPs in 2015, accounting for a quarter of total Hg (THg) emissions from global CFPPs.15Wilson S. Kindbom K. Yaramenka K. Steenhuisen F. Munthe J. Technical Background Report for the Global Mercury Assessment 2013. United Nations Environment Programme, 2013Google Scholar,16Zhang, L.; Wang, S.; Wang, L.; Wu, Y.; Duan, L.; Wu, Q.; Wang, F.; Yang, M.; Yang, H.; Hao, J., Updated emission inventories for speciated atmospheric mercury from anthropogenic sources in China. Environ. Sci. Technol. 49, 3185-3194.Google Scholar Moreover, a large number of CFPPs in China are located in densely populated areas, leading to an increase in Hg exposure risks. Thus, CFPPs are important for the elevation of MeHg exposure risk in many areas in China.17Rothenberg S.E. Windham-Myers L. Creswell J.E. Rice methylmercury exposure and mitigation: a comprehensive review.Environ. Res. 2014; 133: 407-423Crossref PubMed Scopus (121) Google Scholar Given that, reducing Hg emissions from CFPPs has been put into China's political agenda. In addition to Hg, CFPPs are major sources of emission of CO2 and pollutants such as PM2.5, SO2, and NOx. The control of CO2 and air pollution from CFPPs has been prioritized in China's national political agenda because China has been confronted with mounting international and domestic pressures to mitigate CO2 emissions and improve the ambient air quality.18Wu R. Liu F. Tong D. Zheng Y. Lei Y. Hong C. Li M. Liu J. Zheng B. Bo Y. et al.Air quality and health benefits of China’s emission control policies on coal-fired power plants during 2005–2020.Environ. Res. Lett. 2019; 14: 094016Crossref Scopus (32) Google Scholar China's central and local governments have been retrofitting CFPPs in the context of the energy revolution. These retrofitting measures can be generally categorized into three types: (1) small unit shutdown (SUS) aimed at units with a capacity less than 300 MW;19National Development and Reform Commission of China Ultra-Low Emission and Energy Saving of Coal-Fired Power Plant Plan (2014-2020).2014Google Scholar (2) installation of efficient air pollutant control devices (APCDs) for reducing air pollutants, including PM2.5, SO2, and NOx; and (3) power generation efficiency (PGE) improvement via upgrading generation technologies. It has been verified that these retrofitting measures have made great contributions to the reduction of air pollutant and greenhouse gas emissions.18Wu R. Liu F. Tong D. Zheng Y. Lei Y. Hong C. Li M. Liu J. Zheng B. Bo Y. et al.Air quality and health benefits of China’s emission control policies on coal-fired power plants during 2005–2020.Environ. Res. Lett. 2019; 14: 094016Crossref Scopus (32) Google Scholar,20Tong D. Zhang Q. Liu F. Geng G. Zheng Y. Xue T. Hong C. Wu R. Qin Y. Zhao H. Current emissions and future mitigation pathways of coal-fired power plants in China from 2010 to 2030.Environ. Sci. Technol. 2018; 52: 12905-12914Crossref PubMed Scopus (56) Google Scholar,21Liu K. Wu Q. Wang L. Wang S. Liu T. Ding D. Tang Y. Li G. Tian H. Duan L. Measure-specific effectiveness of air pollution control on China’s atmospheric mercury concentration and deposition during 2013–2017.Environ. Sci. Technol. 2019; 53: 8938-8946Crossref PubMed Scopus (41) Google Scholar For instance, the installation of APCDs resulted in the reduction of emissions of SO2, NOx, and PM2.5 by 20.1, 3.9, and 2.15 Tg, respectively, during 2005–25, and 111,900 premature deaths have been avoided by the reduced PM2.5 exposure.18Wu R. Liu F. Tong D. Zheng Y. Lei Y. Hong C. Li M. Liu J. Zheng B. Bo Y. et al.Air quality and health benefits of China’s emission control policies on coal-fired power plants during 2005–2020.Environ. Res. Lett. 2019; 14: 094016Crossref Scopus (32) Google Scholar In addition, these retrofitting measures also have synergetic effects on reducing Hg emissions,20Tong D. Zhang Q. Liu F. Geng G. Zheng Y. Xue T. Hong C. Wu R. Qin Y. Zhao H. Current emissions and future mitigation pathways of coal-fired power plants in China from 2010 to 2030.Environ. Sci. Technol. 2018; 52: 12905-12914Crossref PubMed Scopus (56) Google Scholar,22Wu Q. Li G. Wang S. Liu K. Hao J. Mitigation options of atmospheric Hg emissions in China.Environ. Sci. Technol. 2018; 52: 12368-12375Crossref PubMed Scopus (43) Google Scholar an important pollutant with global concern. However, these synergetic effects on Hg reduction and their associated health benefits have not yet been assessed. According to the articles of the Minamata Convention, all the parties are required to regularly facilitate the evaluation of mitigation measure effectiveness and provide an assessment of the related impacts on human health. Thus, evaluating the Hg emission reductions and associated health co-benefits from CFPP retrofitting is vital for both fulfilling the international obligation and formulating refined mitigation policies. Scholars have made initial attempts to investigate the impacts of CFPP retrofitting on Hg emissions. For instance, a recent study found that improving APCD's Hg removal efficiency substantially reduced THg emissions (over 40 t) from China's coal power sector during 2013–17.21Liu K. Wu Q. Wang L. Wang S. Liu T. Ding D. Tang Y. Li G. Tian H. Duan L. Measure-specific effectiveness of air pollution control on China’s atmospheric mercury concentration and deposition during 2013–2017.Environ. Sci. Technol. 2019; 53: 8938-8946Crossref PubMed Scopus (41) Google Scholar,23Li J. Wei W. Zhen W. Guo Y. Chen B. How green transition of energy system impacts China's mercury emissions.Earth's Future. 2019; 7: 1406-1407Crossref Scopus (48) Google Scholar However, these studies take all the CFPPs as a whole and cannot explicitly reflect the significant heterogeneity in Hg emissions from individual CFPPs (caused by their strikingly different Hg content in coal and APCD types). Although Liu et al.24Liu K. Wang S. Wu Q. Wang L. Ma Q. Zhang L. Li G. Tian H. Duan L. Hao J. A highly resolved mercury emission inventory of Chinese coal-fired power plants.Environ. Sci. Technol. 2018; 52: 2400-2408Crossref PubMed Scopus (94) Google Scholar compiled a high-resolution inventory on Hg from 1,817 CFPPs in China based on the detailed APCD parameters, the plant-level retrofitting measures' effect on Hg emission changes remains poorly understood. Moreover, existing studies on Hg-related health impacts are at the national or provincial scale.1Giang, A.; Selin, N.E., Benefits of mercury controls for the United States. Proc. Natl. Acad. Sci. U S A. 113, 286-291.Google Scholar,3Chen L. Liang S. Liu M. Yi Y. Mi Z. Zhang Y. Li Y. Qi J. Meng J. Tang X. et al.Trans-provincial health impacts of atmospheric mercury emissions in China.Nat. Commun. 2019; 10: 1484Crossref PubMed Scopus (85) Google Scholar As the real-world retrofitting actions occurred at the plant level, a precise assessment comprehensively considering factors such as local population density and Hg deposition is thus urgently needed to reflect each CFPP's contribution to health benefits. To track the route of Hg exposure and quantify the Hg-related health impacts from China's CFPP retrofitting campaign during the 12th Five-Year Plan (FYP) period (2011–2015), in this study we combine a plant-level Hg emission inventory model and the China Mercury Risk-Source-Tracking Model (CMSTM) (details under Experimental Procedures). According to the specific parameters (e.g., coal consumption, application of APCDs, energy efficiency) of each power plant, high-resolution Hg emission inventories are established to clarify the changes in emissions from CFPPs to the air. The CMSTM model consists of components such as atmospheric transport and deposition of Hg, changes in food MeHg, human intake of MeHg, and related health impacts. Each component tracks an important biogeochemical process between the emissions from the stacks of CFPPs and human health. Based on the above models, we for the first time present a high-resolution map of both Hg reduction and related health benefits from the CFPP retrofitting measures. We then compare the benefits between different retrofitting measures and make targeted suggestions for CFPP retrofitting in different areas by comprehensively considering factors such as CFPP locations and population densities. The findings of this study provide not only a scientific foundation for assessing the implementation of the Minamata Convention on Mercury in China's coal-fired power sector but also useful information for more refined mitigation strategies. The three CFPP retrofitting measures resulted in an overall emission reduction of 23.51 t (72.38% Hg0, 26.82% Hg2+, and 0.80% Hgp) during 2011–2015, equivalent to approximately 20% of the THg emitted by China's CFPPs in 2010. Hg emission reduction occurred in 29 of the 34 provincial regions (Figure 1), among which Jiangsu, Inner Mongolia, and Shandong are the top three provinces with the greatest reductions (Figure 1A). Among the three retrofitting measures, over half of the national total emissions reduction was attributed to the newly installed APCDs, while SUS and PGE had relatively lower contributions. The contributions of the three types of measures in different provinces are shown in Figure 1A. Meanwhile, China's top five state-owned power-generation groups (Huaneng Group, Datang Corporation, Huadian Corporation, Guodian Corporation, and State Power Investment Corporation), accounting for 46.29% of China's total CFPP capacity, contributed more than half of the emissions reductions. The rest of the reductions were made by other large state-owned enterprises, local enterprises (owned by provincial or municipal governments), and private enterprises. Among the three measures, the increasing APCD installation rate made the largest contribution to emission reductions. As illustrated in Figure 1B, 308 CFPPs in 24 provinces were equipped with new pollution control devices such as wet flue gas desulfurization (WFGD) and selective catalytic reduction (SCR) technology, which helped prevent 12.02 t of atmospheric Hg emissions (81.69% Hg0, 17.82% Hg2+, and 0.49% Hgp, see Table S1 for more details). Notably, some of the newly installed APCDs reduced the THg emissions but also led to the growth of Hg2+ or Hgp emissions. For example, as SCR was deployed in many CFPPs, Hg2+ emissions in Anhui and Guizhou increased by 0.09 and 0.04 t, respectively. This is because SCR can change the speciation profile of Hg emissions in flue gas by oxidizing Hg0 to Hg2+.24Liu K. Wang S. Wu Q. Wang L. Ma Q. Zhang L. Li G. Tian H. Duan L. Hao J. A highly resolved mercury emission inventory of Chinese coal-fired power plants.Environ. Sci. Technol. 2018; 52: 2400-2408Crossref PubMed Scopus (94) Google Scholar,25Wu Q. Wang S. Li G. Liang S. Lin C.-J. Wang Y. Cai S. Liu K. Hao J. Temporal trend and spatial distribution of speciated atmospheric mercury emissions in China during 1978–2014.Environ. Sci. Technol. 2016; 50: 13428-13435Crossref PubMed Scopus (162) Google Scholar SUS contributed 9.19 t of Hg emission reductions nationwide (Table S1), second only to the reductions attributed to newly installed APCDs. The power-generation capacity of the decommissioned CFPPs was equivalent to 5% of the national total in 2010, while the associated reduction in Hg emissions was equivalent to 7.75% of the total emissions from China's CFPPs in 2010, indicating that the decommissioned units were more Hg intensive than the national average level. Improving PGE via the recovery and utilization of waste heat is also an effective way to reduce Hg emissions. During the 12th FYP, the national average coal consumption rate (the amount of coal consumption per kilowatt-hour of electricity generated) of China's CFPPs decreased from 312 to 297 g/kWh,10Hu X.F. Laird B.D. Chan H.M.J.E.R. Mercury diminishes the cardiovascular protective effect of omega-3 polyunsaturated fatty acids in the modern diet of Inuit in Canada.Environ Res. 2016; 152: 470-477Crossref PubMed Scopus (21) Google Scholar,18Wu R. Liu F. Tong D. Zheng Y. Lei Y. Hong C. Li M. Liu J. Zheng B. Bo Y. et al.Air quality and health benefits of China’s emission control policies on coal-fired power plants during 2005–2020.Environ. Res. Lett. 2019; 14: 094016Crossref Scopus (32) Google Scholar,19National Development and Reform Commission of China Ultra-Low Emission and Energy Saving of Coal-Fired Power Plant Plan (2014-2020).2014Google Scholar,26China Electricity Council China electric power Yearbook 2011.https://navi.cnki.net/KNavi/YearbookDetail?pcode=CYFD&pykm=YZGDL&bh=Date: 2011Google Scholar while PGE reduced atmospheric Hg emissions by 2.3 t (data for each province are shown in Table S1). The three retrofitting measures prevented 5.10 t of atmospheric Hg deposition in China, of which 2.38 t was from CFPP shutdown, 2.17 t from APCD installation, and 0.55 t from PGE. Figure 2 illustrates the spatial distributions of the reductions in atmospheric Hg deposition over China. Among all provincial regions, the Hg deposition reduction was the greatest in Inner Mongolia (0.38 t), followed by Shandong (0.36 t) and Hebei (0.35 t). It is interesting to note that there is a significant mismatch between Hg emission reduction and deposition in many regions. Although the reduction in Hg emissions is higher in Jiangsu (0.26 t) than in Inner Mongolia, the reduction in atmospheric Hg deposition over Inner Mongolia is 1.5 times greater than that over Jiangsu. The explanation for this phenomenon is that Inner Mongolia is a much larger territory than Jiangsu and therefore experienced a greater reduction in atmospheric Hg deposition compared with other regions. The air transport effect also played a vital role in the reduction of Hg depositions in each province. It was found that, for the provinces with the top 10 largest Hg reductions, more than half of the reductions in Hg depositions resulted from decreases in the Hg transported from other provinces, especially from their neighboring provinces (summarized in Table S2). For example, Hg deposition in Hebei decreased by 0.35 t, but less than one-third of this decrease was derived from local CFPPs within Hebei's territory. The largest transregional contributors to deposition reduction in Hebei were Shandong (0.08 t), Shanxi (0.04 t), and Inner Mongolia (0.04 t). Although there was no reduction in Hg emissions in Xizang, the province experienced a decline of 0.06 t in Hg deposition due to the emission reduction measures of CFPPs in other provincial regions. The THg reductions from CFPP retrofitting prevented 30,484.77 total points of IQ decrement and 114 deaths from fatal heart attacks (points and deaths hereafter) in total during 2011–2015 compared with 2010, equivalent to 9.09% and 9.26% of the total IQ decrement and deaths from fatal heart attacks caused by the Hg emissions from CFPPs in China in 2010.3Chen L. Liang S. Liu M. Yi Y. Mi Z. Zhang Y. Li Y. Qi J. Meng J. Tang X. et al.Trans-provincial health impacts of atmospheric mercury emissions in China.Nat. Commun. 2019; 10: 1484Crossref PubMed Scopus (85) Google Scholar As illustrated in Figure 3, the health benefits in each province had large spatial variability (see details in Table S3), and approximately 70% of the contributions (10,720.97 points and 78 deaths) came from the top 10 provincial regions with the greatest emission reductions. Among the three emission reduction measures, the largest health benefits came from SUS, which contributed to the prevention of 15,374.63 points of IQ decrement and 59 deaths. It is interesting to note that the SUS-associated reduction in Hg deposition was greater in Inner Mongolia than in Jiangsu, but the number of avoided deaths associated with SUS in Jiangsu was more than 10-fold greater than that in Inner Mongolia, as Jiangsu has a much higher population density and MeHg concentration in consumed food.3Chen L. Liang S. Liu M. Yi Y. Mi Z. Zhang Y. Li Y. Qi J. Meng J. Tang X. et al.Trans-provincial health impacts of atmospheric mercury emissions in China.Nat. Commun. 2019; 10: 1484Crossref PubMed Scopus (85) Google Scholar Although reduced Hg emissions were more from the installation of APCDs than the SUS, the former contributed less to health benefits (11,858.16 points and 43 deaths) than the latter. The health benefits associated with newly installed APCDs were undermined by devices such as SCR, which removes THg emissions from the flue gas and change the Hg species by increasing the proportions of Hg2+ and HgP that are easily deposited, thus adversely affecting human health.1Giang, A.; Selin, N.E., Benefits of mercury controls for the United States. Proc. Natl. Acad. Sci. U S A. 113, 286-291.Google Scholar Therefore, an undesirable situation occurred in Anhui Province: the health risks related to Hg pollution increased despite deceasing THg emissions. Compared with SUS and the installation of APCDs, PGE had much smaller contribution to health benefits (3,251.99 points and 12 deaths). Regarding the health benefits gained by Hg reduction through efficiency improvement nationwide, only Zhejiang and Sichuan avoided more than 1 death. Most of the reductions in health impacts associated with PGE (prevented IQ decrement and fatal heart attacks: 2,425.76 points and 9 deaths) and APCD installation (10,702.69 points and 39 deaths) were attributed to large CFPPs with capacities over 300 MW, accounting for 74.36% and 89.80% of the total reductions, respectively. In particular, CFPPs with capacities over 1200 MW contributed more than half of the health benefits associated with the installation of APCDs. In contrast, the CFPPs with capacities under 100 MW accounted for only approximately 8% and 3% of the health benefits related to PGE improvement and the installation of APCDs, respectively. The CFPP shutdown campaign showed a completely different picture. As this campaign mainly targeted small units, almost two-thirds of the health benefits gained by CFPP decommission (9,407.32 points and 37 deaths) were from CFPPs with capacities less than 300 MW. The CFPPs from the five power-generation groups were the leading contributors to the observed health benefits and were responsible for half and two-fifths of the health benefits associated with the newly installed APCDs and decommissioned CFPPs, respectively. Among the five groups, the Huaneng Group made the largest contribution (prevented IQ decrement and fatal heart attacks: 4,732.85 points and 18 deaths) to the health benefits, especially for the health benefits of newly installed APCDs. Furthermore, an IQ decrement of 2,610.71 and 10 deaths were avoided by SUS of the Guodian Corporation, ranking first among the five groups. The local CFPPs in different regions were the second largest contributor, responsible for approximately 30% of the health benefits of SUS and 20% of the health benefits of the other two retrofitting measures. Moreover, half of the decommissioned CFPPs with capacities less than 100 MW belonged to local enterprises, which have higher emission intensity and lower energy efficiency. The rest of the health benefits were attributed to individual and private enterprises, captive power plants, and other large state-owned enterprises (i.e., China Resources Group and State Grid Corporation of China). Notably, not all CFPP retrofitting measures resulted in health benefits; for instance, health impacts slightly increased because of the newly installed SCR device of a captive CFPP-Taigang stainless steel power plant. As the sources of health benefits related to reductions in Hg deposition were clearly identified in the atmospheric transport model, the transregional effects on health benefits (namely, the source-receptor relationship of health benefits between provincial regions) are illustrated (Figure 4). The three provinces that received the largest cross-boundary health benefits were Zhejiang, Guangdong, and Jiangsu, while Shandong, Jiangsu, and Hebei served as the largest contributors to other provinces. For example, 5 of the 10 deaths avoided in Jiangsu Province were attributable to CFPP retrofitting measures in other provincial regions, such as Shandong (14.44%), Hebei (5.74%), and Inner Mongolia (4.53%). The majority of deaths avoided in Shandong (55.05%) and Hebei (71.69%) were credited to the implementation of the three types of CFPP retrofitting efforts in other provinces. The retrofitting measures in Shandong prevented 13 deaths in other provinces, accounting for over 80% of the total contributions of Shandong, and the largest beneficiaries were Jiangsu (9.19%), Zhejiang (8.91%), and Shanghai (8.73%). Meanwhile, these three measures also exerted transregional effects on IQ decrement. More than half of the avoided IQ decrement in Hebei, Shandong, and Jiangsu was associated with Hg reductions from CFPPs in other provincial regions