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Heavy Metals in Atmospheric Particulate Matter: A Comprehensive Understanding Is Needed for Monitoring and Risk Mitigation Huiming Li, Xin Qian,* and Qin’geng Wang State Key Laboratory of Pollution Control and Resources Reuse, School of the Environment, Nanjing University, 163 Xianlin Avenue, Nanjing 210023, China heavy metals are important components of PM in the atmospheric environment and they have complex pollution feature. There are still several potentially important problems that require special attention and further study before we will have a comprehensive understanding of the occurrence and behavior of heavy metals in PM. First, when compared with coarse PM, fine particulate matter (PM2.5, particles with aerodynamic diameters ≤2.5 μm) has a greater surface area per unit mass, allowing PM2.5 to accumulate heavy metals more effectively; PM2.5 is also more hazardous than coarser PM because of its longer residence time in the atmosphere and deeper penetration into the lungs.1 The standards or reference values for atmospheric Pb, Cd, As, Ni, and Cr (VI) concentrations proposed by the European Union and the World Health Organization,4 as well as the newest Chinese “Ambient Air Quality Standards” (GB3095−2012) which were issued in 2012, are currently based on heavy metal concentrations in coarse PM. Atmospheric Hg concentrations are determined as elemental mercury vapor (Hg 0).4 Although monitoring data may be appropriate to meet safety standard requirements, ambient heavy metal concentrations and the extent of adverse effects caused by heavy metals in PM2.5 rban atmospheric pollution is one of the most serious remain uncertain. It is necessary to conduct more surveys and global environmental issues of the past decade. analyses on heavy metals in fine PM or even ultrafine PM Atmospheric particulate matter (PM) is of great concern to (PM0.1, particles with aerodynamic diameters ≤0.1 μm) to the public and to government agencies because of the health improve the usefulness of monitoring atmospheric heavy effects and haze episodes associated with it. PM has the strong metals. potential for adsorbing toxic metals, which may then enter the Second, the total amount of heavy metals in the environment human body through inhalation and have adverse physiological is usually used as the main or only evaluation criteria in effects. Exposure to PM has been linked to a wide range of assessing the pollution conditions. However, it is generally diseases, including cardiovascular and respiratory diseases and recognized that the chemical speciation of a heavy metal lung cancer.1 There is growing evidence that heavy metals probably determines its bioavailability and the potential risks it adsorbed to PM are crucial to the toxicity and adverse health poses to the environment and to human health.5 The heavy effects of PM.2 Metal elements adsorbed to atmospheric PM metal chemical speciation in a solid environmental sample can can also be deposited to soils, water bodies, and plant leaves via generally be determined by sequentially extracting the different wet and dry deposition. They may then accumulate in plants or species as the adsorbed−exchangeable carbonate phase, the animals through biochemical processes; and humans may then reducible phase, the oxidizable phase, and the residual fraction.5 The first three of those species types, especially the adsorbed− be exposed by consumption of contaminated plants or animals. exchangeable carbonate phase, are considered to be more In order to control the atmospheric heavy metal pollution, it is mobile in the environment and more hazardous to organisms essential to conduct effective environmental risk management. than is the resistant fraction.5 Attention should therefore be Rapid evaluation models on spatiotemporal distributions of paid to the chemical speciation of heavy metals in PM. heavy metals and practical early warning programs could be Third, PM can either be directly emitted into the air developed by combining the monitoring data with interdiscipli(primary PM), or it can be formed secondarily in the nary research, such as atmospheric pollutant diffusion models, epidemiological investigations, toxicological experiments, and geographical information systems. Recent scientific research on Received: June 9, 2013 heavy metals in PM has been focused on the pollution levels, Revised: November 7, 2013 source analysis, temporal variations, spatial distributions, and Accepted: November 15, 2013 Published: November 19, 2013 health effects of heavy metals adsorbed to PM.2,3 However,
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dx.doi.org/10.1021/es404751a | Environ. Sci. Technol. 2013, 47, 13210−13211
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(3) Hu, X.; Zhang, Y.; Ding, Z. H.; Wang, T. J.; Lian, H. Z.; Sun, Y. Y.; Wu, J. C. Bioaccessibility and health risk of arsenic and heavy metals (Cd, Co, Cr, Cu, Ni, Pb, Zn and Mn) in TSP and PM2.5 in Nanjing, China. Atmos. Environ. 2012, 57, 146−152. (4) Commission of the European Communities. Directive 2004/ 107/EC of the European Parliament and of the Council of 15 December 2004 relating to arsenic, cadmium, mercury, nickel and polycyclic aromatic hydrocarbons in ambient air, 2004. http://eur-lex. europa.eu/LexUriServ/site/en/oj/2005/l_023/l_ 02320050126en00030016.pdf. (5) Pérez, G.; López-Mesas, M.; Valiente, M. Assessment of heavy metals remobilization by fractionation: comparison of leaching tests applied to roadside sediments. Environ. Sci. Technol. 2008, 42 (7), 2309−2315.
atmosphere from gaseous precursors (mainly sulfur dioxide, nitrogen oxides, ammonia, and nonmethane volatile organic compounds).1 Secondary aerosols are mainly formed through chemical/physical processes in the atmosphere and can be affected by meteorological factors.1 Metal compounds are an important class (by chemical composition) of PM, and their concentrations and constituents have been found to vary seasonally in the atmosphere in cities.3 However, it is still unknown whether meteorological factors may affect the characteristics of heavy metals in PM. Furthermore, it would be meaningful to study the effects of the changes of climatic factors nowadays on atmospheric heavy metal pollution as this would enable us to better understand the transportation, transformation, and the environmental influence of atmospheric PM in the worldwide. Heavy metals in PM have the potential for long-range transportation; this makes it difficult to identify the pollution source areas. Therefore, the temporal and spatial distributions of heavy metals in PM should be studied in detail. Finally, heavy metals in the urban atmosphere are mainly derived from industrial activities (mining, smelting, and fossil fuel combustion), traffic emissions (vehicle exhausts and the products of wear from tires, brake linings, and bearings), and natural sources (minerals, forest fires, and oceans). Atmospheric heavy metal concentrations are actually dependent on the natural background concentrations, economic development level and the overall planning features of a city. A country’s energy production and use patterns are likely closely linked to atmospheric heavy metal pollution, especially in developing countries, many of which derive most of their energy from fossil fuels. For instance, China now produces and consumes more coal than any other country. According to the China Statistical Yearbook 2012, the total energy consumption in China was about 3.48 billion tons of SCE (standard coal equivalent) in 2011; and coal accounted for 68.4% of the total energy consumption, followed by crude oil which accounted for 18.6%. It would be beneficial to study the relationship between energy consumption parameters and atmospheric heavy metal pollution, to provide a useful reference for the revision of urban development planning and environmental policies.
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AUTHOR INFORMATION
Corresponding Author
*X.Q.) Phone: +86 25 89680527; fax: +86 25 89680527; email:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS
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REFERENCES
This work was supported by the National Natural Science Foundation of China (No. 41271511).
(1) World Health Organization (WHO). Health Risks of Particulate Matter from Long-Range Transboundary Air Pollution; WHO Regional Office for Europe, 2006. (2) Bollati, V.; Marinelli, B.; Apostoli, P.; Bonzini, M.; Nordio, F.; Hoxha, M.; Pegoraro, V.; Motta, V.; Tarantini, L.; Cantone, L.; Schwartz, J.; Bertazzi, P. A.; Baccarelli, A. Exposure to metal-rich particulate matter modifies the expression of candidate microRNAs in peripheral blood leukocytes. Environ. Health Perspect. 2010, 118 (6), 763−768. 13211
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