The local impact of a coal-fired power plant on inorganic mercury and methyl-mercury distribution in rice (Oryza sativa L.)☆
Introduction
Mercury (Hg) is a highly toxic and non-essential element (Clarkson, 1998). Both inorganic and organic forms exist in the environment. The inorganic Hg (Hg(II)) can be transformed into methyl-mercury (MeHg), the most toxic Hg form, under certain conditions. The health risks posed by MeHg due to its bio-magnification in the aquatic food chain are well-known. Trace amounts of MeHg in water can result in much higher and harmful concentrations of MeHg in fish and their predators. The consumption of fish has been considered as the major pathway for human MeHg exposure (WHO, 1990).
Studies have recently reported that the consumption of rice rather than fish is the major pathway for human exposure to both MeHg and Hg(II) in Hg mining regions of China (Qiu et al., 2008, Zhang et al., 2010a, Li et al., 2015). Rice is a diet staple for many people around the world, with daily intake up to 0.5 kg (dry weight) for the majority of the Chinese population as well as in a number of other Asian countries (Zhang et al., 2010b, Rothenberg et al., 2014). The positive correlation, which was observed between rice MeHg intake and hair MeHg levels in residents from Hg mining areas, confirmed that the primary pathway of MeHg exposure was via rice consumption (Zhang et al., 2010a). A significant positive correlation between paired results for urine Hg concentrations and serum creatinine was observed, suggesting that renal injury may occur in local populations due to Hg(II) exposure (Li et al., 2015).
Coal-fired power plants are considered as the major anthropogenic source of atmospheric Hg around the world and currently contribute to approximately 47% of the industrial Hg emissions in China (UNEP., 2010, Yin et al., 2014, Xu et al., 2016). Although gaseous elemental Hg (GEM) emitted from power plants can be transported over long distances, significant amounts of oxidized and particulate forms are deposited nearby. Thus the most highly impacted areas are in the vicinity (around 3 km) of the power plants (Carpi, 1997, Flues et al., 2002, Keeler et al., 2006). Due to China's rapidly growing economy, coal burning power plant associated Hg discharged into the atmosphere have also increased at a high speed, resulting in local Hg deposition loads in China that are 1–2 orders of magnitude higher than those found in North America and Europe (Fu et al., 2012).
Studies have revealed that atmospheric Hg deposition had a direct correlation with MeHg accumulation in aquatic food webs (Fitzgerald and Hammerschmidt, 2005, Hammerschmidt and Fitzgerald, 2006, Orihel et al., 2007). Similarly, high rates of atmospheric Hg deposition leads to high MeHg in rice grains at Hg contaminated sites even when the rice grows in uncontaminated soils transported in from background areas rather than in local contaminated soil (Meng et al., 2011). Researchers also found that variations in atmospheric Hg deposition can have immediate impacts on fish Hg concentrations (Hrabik and Watras, 2002). These studies postulated that the amount of new Hg deposition to the ecosystem is an important source of bioavailable Hg(II) ready for introduction into the food web. This suggests that once the atmospheric Hg deposition near an emission source is enhanced, then a corresponding increase of MeHg in the biota could be expected.
Rice shows a strong capacity to bio-accumulate MeHg in its grains (Zhang et al., 2010b). Rice is generally cultivated in water-flooded conditions, which generate reducing conditions in soil that are conducive to net Hg(II)-methylation. MeHg in the soil and water can then be taken up by rice roots and then stored in the grains (Meng et al., 2012). In mercury mining areas, it has been shown that newly deposited mercury is easier to be converted into MeHg and then accumulated in rice (Meng et al., 2011). Nevertheless, it is not well known whether local deposition of Hg emitted from coal-fired power plants will affect absorption of Hg(II) and MeHg in rice plants. Currently in China, large numbers of paddy fields are located near coal-burning power plants (Qin et al., 2008, Xuan et al., 2004), therefore, it is of great importance to evaluate the impact of Hg emission from coal-fired power plants on both Hg(II) and MeHg accumulation in rice cultivated in the vicinity of the power plants.
China is the greatest contributor of SO2 in the world, and coal burning power plant facilities are the biggest emission source, contributing for half of the overall SO2 emission in 2005 (Stern, 2005, Xu, 2010). Anthropogenic S deposition rates several times higher than natural S deposition rates increase the S level in soil (Eriksson et al., 1992). As the significance of sulfate reducing bacteria (SRB) for mercury methylation procedure, increased SO42− will do contribution to enhanced Hg(II)-methylation in lake and terrestrial ecosystems (Compeau and Bartha, 1985; Orem et al., 2011, Marvin-DiPasquale et al., 2014). Human activities can not only influence climate but also S and Hg loading to the environment (Åkerblom et al., 2013). Some researches show the availability of SO42− for SRB and the bioavailability of inorganic Hg-sulfur compounds play a crucial role in regulating the MeHg level in mire (Skyllberg, 2008). Sulfate amendment experiments to mires indicate a positive relationship with net MeHg production (Jeremiason et al., 2006, Åkerblom et al., 2013).
The current study displayed characteristics of Hg(II) and MeHg in rice effected by S and GEM from proximity to a coal-fired power plant. We hypothesized that close proximity to a coal-fired power plant would enhanced Hg and S deposition, which will result in more S and Hg in paddy soil and subsequently enriched Hg(II) and MeHg concentrations in rice in the environment nearby a coal-fired power plant compared with the reference locations further away. However, we do not know the exact mechanism and distribution characteristics of Hg(II) and MeHg in rice in the vicinity of a coal-fired plant. This study is an initial step in testing our hypothesis and the first time the impact from power plants on nearby rice has been evaluated.
Section snippets
Experimental and materials
The Yueyang Coal-fired Power Plant (YCPP) was selected for the investigation. This is the largest coal fired power plant in Yueyang City (population 5.3 million), Hunan Province, China. With a total capacity of 2 × 600 MW, the YCPP is also the biggest power facility of its kind in Hunan province, China. The flue gas desulphurization (FGD) technique was employed in 2006, which typically reduces Hg emissions by 78% (Nolan et al., 2004, Zhang et al., 2008). The YCPP is adjacent to the Xiangjiang
MeHg and Hg(II) in rice
In rice samples, MeHg concentrations varied from 1.7 to 3.8 μg kg−1 with a mean of 2.4 ± 0.72 μg kg−1 (n = 13). The maximum MeHg concentrations in rice were observed at the sites 1.5 km and 5 km from the YCPP (Fig. 2). The correlation between rice MeHg concentrations and distance from the YCPP was not significant (r = 0.56, p < 0.5), even if there is a positive tendency.
In rice samples, Hg(II) concentrations varied from 2.0 to 22 μg kg−1 with an mean value of 5.7 μg kg−1 (n = 13). Hg(II)
MeHg and Hg(II) in rice
The highest concentrations of rice MeHg were obtained 5 km away from the YCPP. Both the petroleum refinery and cement plant are located in this vicinity and may be contributing to MeHg accumulation in rice. The highest Hg(II) concentration in rice was obtained near 2 km from the YCPP (Fig. 2), and the concentrations of Hg(II) decline sharply then remained steady with distance from YCPP. There was however, slightly more Hg(II) in the site near the refinery and cement factories than further away.
Conclusions
This study demonstrates that the Hg emissions from coal-fired power plants can increase both the Hg(II) and MeHg of rice. Positive correlations of rice MeHg with soil Hg species, soil S, and GEM were observed. Furthermore, we also found indications that other facilities significantly contributed to the MeHg production in the soil. The ambient air GEM and soil S both enhanced MeHg levels in rice. Nevertheless, soil S was also negatively correlated to rice uptake of Hg(II) from soil. Since the
Acknowledgments
This study was supported by the National Key Basic Research Program of China (2013CB430004), the External Cooperation Program of BIC, Chinese Academy of Sciences, Grant No.132852KYSB20130003, the Sino-Swedish Mercury Management Research Framework (SMaReF, Grant No. 2013-15586-107068-84), and by the National Natural Science Foundation of China (41173126, 41373135, and 41203091). The authors gratefully acknowledge the support of all persons involved in the project.
References (74)
- et al.
Significant interaction effects from sulfate deposition and climate on sulfur concentrations constitute major controls on methylmercury production in peatlands
Geochimica Cosmochimica Acta
(2013) - et al.
Selective extractions to assess the biogeochemically relevant fractionation of inorganic mercury in sediments and soils
Anal. Chim. Acta
(2003) - et al.
Accumulation of atmospheric mercury in forest foliage
Atmos. Environ.
(2003) - et al.
Urban environmental mercury in Changchun, a metropolitan city in Northeastern China: source, cycle, and fate
Sci. Total Environ.
(2004) - et al.
The influence of a coal-fired power plant operation on radionuclide concentrations in soil
J. Environ. Radioact.
(2002) - et al.
A review of studies on atmospheric mercury in China
Sci. Total Environ.
(2012) - et al.
Recent declines in mercury concentration in a freshwater fishery: isolating the effects of de-acidification and decreased atmospheric mercury deposition in Little Rock Lake
Sci. Total Environ.
(2002) - et al.
Fractionation studies of mercury in soils and sediments: a review of the chemical reagents used for mercury extraction
Anal. Chim. Acta
(2009) - et al.
Human inorganic mercury exposure, renal effects and possible pathways in Wanshan mercury mining area, China
Environ. Res.
(2015) - et al.
Simple solvent extraction technique for elimination of matrix interferences in the determination of methylmercury in environmental and biological samples by ethylation-gas chromatography-cold vapor atomic fluorescence spectrometry
Talanta
(1996)
Atmospheric mercury species measured in Guiyang, Guizhou province, southwest China
Atmos. Res.
Methylmercury production in sediment from agricultural and non-agricultural wetlands in the Yolo Bypass, California, U. S. A.
Sci. Total Environ.
Demonstration of additive use for enhanced mercury emissions control in wet FGD systems
Fuel Process. Technol.
Rice methylmercury exposure and mitigation: a comprehensive review
Environ. Res.
Pollutants emitted by a cement plant: health risks for the population living in the neighborhood
Environ. Res.
The speciation and bioavailability of mercury in sediments of Haihe River, China
Environ. Int.
Global sulfur emissions from 1850 to 2000
Chemosphere
Mercury speciation and emissions from coal combustion in Guiyang, southwest China
Environ. Res.
Atmospheric mercury in Changbai Mountain area, northeastern China I. The seasonal distribution pattern of total gaseous mercury and its potential sources
Environ. Res.
Mercury emissions from six coal-fired power plants in China
Fuel Process. Technol.
Examination of total mercury inputs by precipitation and litterfall in a remote upland forest of Southwestern China
Atmos. Environ.
In situ sulphate stimulation of mercury methylation in a boreal peatland: toward a link between acid rain and methylmercury contamination in remote environments
Glob. Biogeochem. Cycles
Separation of risks and benefits of seafood intake
Environ. Health Perspect.
Mercury from combustion sources: a review of the chemical species emitted and their transport in the atmosphere
Water, Air, Soil Pollut.
Human toxicology of mercury
J. Trace Elem. Exp. Med.
Sulfate-reducing bacteria: principal methylators of mercury in anoxic estuarine sediment
Appl. Environ. Microbiol.
Acidification of forest soils in Sweden
Ambio
Assessing the influence of different atmospheric and soil mercury concentrations on foliar mercury concentrations in a controlled environment
Water, Air, Soil Pollut.
Temporal variation of total gaseous mercury in the air of Guiyang, China
J. Geophys. Res. Atmos.
Human exposure to methylmercury through rice intake in mercury mining areas, Guizhou Province, China
Environ. Sci. Technol.
Methylmercury in mosquitoes related to atmospheric mercury deposition and contamination
Environ. Sci. Technol.
National Safety Standards for Foods and Maximum Levels of Contaminant in Foods
Sulfate stimulation of mercury methylation in freshwater sediments
Environ. Sci. Technol.
Methylmercury in freshwater fish linked to atmospheric mercury deposition
Environ. Sci. Technol.
Foliar exchange of mercury vapor: evidence for a compensation point
Water, Air, Soil Pollut.
Bonding of Hg (II) to reduced organic sulfur in humic acid as affected by S/Hg ratio
Environ. Sci. Technol.
Cited by (48)
Distribution and bioavailability of mercury in size-fractioned atmospheric particles around an ultra-low emission power plant in Southwest China
2024, Journal of Environmental Sciences (China)Characterization of atmospheric mercury from mercury-added product manufacturing using passive air samplers
2023, Environmental PollutionTracking the multiple Hg sources in sediments in a typical river-lake basin by isotope compositions and mixing models
2023, Journal of Hazardous MaterialsHeavy metal(loid)s in agricultural soils in the world's largest barium-mining area: Pollution characteristics, source apportionment, and health risks using PMF model and Cd isotopes
2022, Process Safety and Environmental ProtectionCitation Excerpt :Agricultural soil (0–20 cm depth, n = 103), soil profile (n = 3), lichen (n = 5), fertilizer (n = 2), ore (n = 3), and slag (n = 5) samples were collected in July 2021 (Fig. 1) and stored in polyethylene zip-lock bags before natural air-drying. Samples were then milled to powder in an agate mortar to pass through a 200-mesh sieve (74 µm) and stored in zip-lock bags pending digestion (Ma et al., 2017a; Xu et al., 2017). The samples were digested in customized autoclaves (Tan et al., 2020).
Risk assessment and driving factors of trace metal(loid)s in soils of China
2022, Environmental Pollution
- ☆
This paper has been recommended for acceptance by Prof. W. Wen-Xiong.