Review ArticleEnvironmental mercury contamination in China: Sources and impacts☆
Introduction
Mercury (Hg) is one of the most toxic heavy metals commonly found in the global environment including lithosphere, hydrosphere, atmosphere and biosphere. A series of complex chemical transformations allows the three-oxidation states of Hg to cycle in the environment (Barbosa et al., 2001). Most of the Hg encountered in all environmental media (water/soil/sediments/biota) is in the form of inorganic mercuric salts and organomercurics, with the sole exception of atmosphere. The mercuric salts HgCl2, Hg(OH)2 and HgS are the prevalent forms existing in the environment and CH3HgCl and CH3HgOH are main forms of organic compounds, together with other organomercurics (i.e., dimethylmercury and phenylmercury) existing in small fractions (USEPA, 1997a).
Natural, anthropogenic and re-emitted sources are the three major sources of Hg emissions (USEPA, 1997b), whereas the most important anthropogenic sources of Hg pollution in the environment are urban discharges, agricultural materials, mining and combustion and industrial discharges. Atmospheric deposition is an important pathway for Hg deposition into the environment. The amount of Hg in the atmosphere is estimated to have increased as much as ten-fold since the beginning of the industrial revolution (USEPA, 2003); moreover, it was indicated that the total amount of Hg emission into atmosphere from natural sources, including volcanoes, soils, forests, lakes and open oceans, was 2000 t annually in the world (Mason et al., 1994), while that amount from anthropogenic sources, mainly due to combustion and waste incineration, was 2000–2200 t annually (Seigneur et al., 2004) and the amount re-emitted of previously deposited Hg was about 2000 t annually (Bergan et al., 1999). Emission inventories indicate that Asian Hg sources account for more than 50% of the global anthropogenic total Hg (Jaffe et al., 2005). In the next few decades, a significant increase in anthropogenic Hg emissions in Asia is likely, owing to rapid economic and industrial development, unless drastic measures are taken (Wong et al., in press). This is especially so for China, as she has become a major player in steel production, which grew considerably to 22.8% (220 Mt) of the world's output in 2003 compared to 12.3% in 1993 (Sweeny, 2004), and also a consumer of large quantities of coal (1270 Mt), with 26.2% of the world's total coal consumption in 2001, a 23% increase from 1990 (USEIA, 2005).
This article is an attempt to review the current status of the major sources of Hg emissions in China, their fates in different environmental matrixes, and environmental and health effects. Two case studies are cited to illustrate the potential human health impacts: one deals with the Hg concentrations in residents of Songyuan City (Jilin Province), northeast China, 20 years after the closure of an acetic acid plant, and the other with subfertility in men and skin disorder and autism in children due to fish consumption in Hong Kong, south China.
Section snippets
Sources of Hg contamination in Chinese cities
It has been estimated that the amount of total Hg emissions were 536 (± 236) t from China in 1999. Mercury emission from non-ferrous metals smelting, coal combustion, and miscellaneous activities, of which battery and fluorescent lamp production and cement production are the largest, contributed about 45%, 38% and 17%, respectively, to the total Hg emission (Streets et al., 2005).
Mercury levels in air
Elemental Hg (Hg0) and divalent Hg (Hg(II)) are the major forms existing in atmosphere. Moreover, the latter is composed of gaseous divalent Hg (Hg2+) and particulate divalent Hg (Hgp) (USEPA, 1997b). Compared with a relatively much shorter atmospheric lifetime of hours to divalent Hg species, the average residence time of Hg0 in atmosphere is a longer period of 0.5–2 years, which allows Hg0 to transport to far distances in the atmosphere and contributes to the Hg global cycling (USEPA, 1997b).
Mercury exposure pathways
Inhalation, consumption of water, fish and other food items and ingestion of soil are common human Hg exposure routes, with Hg usually in the inorganic forms and of very low concentration. After inhalation of Hg by human beings, elemental Hg vapor rapidly diffuses through the alveolar membrane and is absorbed through the lungs. Exposure to more than 100,000–200,000 ng/m3 of elemental Hg vapor for a few hours can cause acute chemical bronchiolitis and pneumonitis, and the threshold limit of
Northern China, 20 years after closure of an acetic acid plant
Songhua River in Jilin Province was heavily polluted by Hg due to an acetic acid plant in the 1960s. Ninety-two percent of fish collected from the river contained Hg in excess of 0.4 mg/kg, resulting in 13.5 mg/kg (highest value 118.8 mg/kg) of Hg in fishermen's hair. MeHg poisoning due to overconsumption of contaminated fish was noted in some fishermen. Drainage of wastewater from the plant was terminated in 1982 (Wu, 1984). A comprehensive survey was conducted 20 years later (2002–2005) to
Conclusion
Metal smelting (especially Zn smelting) and coal combustion (especially industrial and power plants) are the two major sources for Hg contamination in the environment. The limited amount of data available indicated Hg contamination existed in different ecological compartments in China. Fish consumption is the main exposure pathway of Hg to certain populations, especially coastal populations (such as Hong Kong) that consume a larger amount of fish. In addition, due to the serious Hg
Acknowledgements
Financial support from the Group Research, Central Allocation, Research Grants Council of the University Grants Committee of Hong Kong is gratefully acknowledged. The authors thank Ms. Ursula Absalom and Dr. Leung for improving the paper.
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“Capsule”: mercury contamination in different ecological compartments in China has potential adverse health effect to populations with high fish consumption and people living near power plants.