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Emerging Thallium Pollution in China and Source Tracing by Thallium Isotopes Juan Liu,† Jin Wang,† Daniel C.W. Tsang,‡ Tangfu Xiao,† Yongheng Chen,† and Liping Hou*,†
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College of Environmental Science and Engineering, Guangzhou University; Innovation Center and Key Lab of Waters Safety & Protection in the Pearl River Delta, Ministry of Education, Guangzhou 510006, China ‡ Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong China activities has not been accounted for until recently. As displayed in Figure 1, localized high-Tl pollution zones have been discovered in the northern and western areas of Guangdong, southwestern Guizhou, and in several areas in Yunnan, Anhui, Guangxi, and Hubei.1 The main emissions of Tl to the environment arise not from the use of Tl as a product but from certain industrial processes wherein Tl is present as an impurity in the raw materials. These Tl pollution incidents are predominantly ascribed to the mining and smelting of Tlbearing sulfide ores (e.g., pyrite, galena, sphalerite, lorandite, and arsenite). Tl enrichment occurs not only in sulfide minerals (e.g., Pb-, Zn-, Cu-, As-, Sb-, Fe-, Hg-, and Au-sulfides) but also in minerals in igneous rocks (e.g., mica, alunite, and potassium feldspar) due to both its chalcophilic and lithophilic properties.1,2 In addition to the typical sources of Tl-bearing sulfide ores, the steel industry’s employment of Fe-oxide minerals has emerged as an important source of Tl pollution. Our detailed investigation from a large steel factory in Guangdong revealed that even very low Tl contents (0.02−1.03 mg/kg) as impurities in raw materials can lead to enriched levels of Tl in the dedusting wastewater from sintering furnaces. This hallium (Tl) is one of the most toxic trace metals on finding is likely due to the rapid release and gasification of Tl Earth and can cause both chronic and acute poisoning. Tl compounds from the raw materials under high temperatures is listed by both the United States Environmental Protection (>800 °C) during steel production.2 Notably, the potential Agency (EPA) and the European Union (EU) as a dangerous pollution of over 200 steel factories on the production scale of pollutant. Tl is also considered a priority pollutant in both the millions of tons in China requires further investigation.2 12th and 13th five-year plans in China. Although Tl is highly With accelerating industrialization and the inevitable toxic, it was not included in the list of metals to be supervised utilization of Tl-bearing minerals in various industrial activities, until 2010. Environmental pollution from Tl has received China may face an alarming outbreak of Tl pollution in the coming decades. Additionally, frequent illegal mining and much less attention than other metals, such as Cd, As, Pb, and wastewater discharge in remote areas may have further Hg1. As a trace metal, Tl is usually dispersed throughout the exacerbated Tl pollution. To prevent environmental pollution, natural environment at a very low concentration. However, a series of environmental laws have been recently initiated in there has been a recent outbreak of serious Tl pollution China. Policies are now in place that require environmental incidents in the major rivers of different provinces in China litigation cases to follow a “polluter-pays” principle. However, (Figure 1). This outbreak includes Tl pollution in the Beijiang pollution litigation remains very difficult due to a lack of longRiver of Guangdong in October 2010, the Hejiang River of term monitoring data on Tl pollution from any specific Guangxi in July 2013, some rivers in the city of Xinyu in Jiangxi industry, and industries were driven by the principle of “the during April 2016, the Jialing River crossing Sichuan and GDP as priority” for decades. Shanxi in May 2017, and the Lu River across Hunan and Vague source attribution has inevitably placed the liability Jiangxi in August 2018. These pollution incidents have aroused for cleanup under dispute and has inhibited the remediation extensive public concern, and regulation and surveillance of Tl process and generated associated economic disputes. Meanpollution has been increasingly adopted in China. However, while, “true” Tl sources continue to pollute the environment the story does not end here. In China, Tl-bearing sulfide mineral resources have been exploited and utilized in various industries since the 1960s, but Received: October 10, 2018 the recycling and regulation of Tl pollution related to industrial
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© XXXX American Chemical Society
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DOI: 10.1021/acs.est.8b05282 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
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Environmental Science & Technology
Figure 1. Map showing the areas where Tl-containing minerals have been identified (red dots) to pollute minor (red lines) and major (blue lines) rivers in China.
used as a promising tool to identify sources and pathways of Tl pollution. This tool may provide a new method for forensic analysis of Tl pollution, which can be used to establish a reliable scientific framework for pollution prevention and the “polluter-pays” system.
owing to erroneous judgments. Therefore, the identification of Tl pollution sources and transport pathways is a prerequisite for effective pollution mitigation and prevention. The advent of new, high-precision analytical methods (e.g., multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS)), which enable the resolution of minute variations in the stable isotope compositions of trace elements (e.g., Zn, Hg, Mo, Cu, Fe, Cr, Se, Cd, and Tl) in complex natural samples, facilitates a new avenue for environmental forensic studies. Thallium has only two naturally stable isotopes, with atomic masses of 203 and 205 and relative abundances of 29.5% and 70.5%, respectively.3,4 In practice, the isotopic compositions of Tl (205Tl/203Tl) are best determined by reference to a standard (National Institute of Standards and Technology (NIST) 997 Tl).3,4 Isotopic compositions are reported as ε
205
205
Tl = 10000 × ((
/(
205
203
205
Tl/ Tl sample −
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Juan Liu: 0000-0002-7247-151X Daniel C.W. Tsang: 0000-0002-6850-733X Notes
The authors declare no competing financial interest.
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203
Tl/ TlNIST997)
ACKNOWLEDGMENTS This project was supported by the National Natural Science Foundation of China (Nos. 41573008, 41873015, 41573119, 41773011 and U1612442), the Natural Science Foundation of Guangdong Province, China (2014A030313527 and 2017A030313247), the "Challenge Cup" Undergraduate Project, the Rural Non-point Source Pollution Comprehensive Management Technology Center of Guangdong Province, the High Level University Construction Project of Guangdong Province (Regional Water Environment Safety andWater Ecological Protection) and the Guangzhou University’s 2017 training program for young top-notch personnel
203
Tl/ TlNIST997))
Pertinent research has studied Tl isotopic compositions in marine and crustal environments to investigate the origin and evolution of natural processes.3 Recent studies have found obvious Tl fractionation during industrial processes. Notable Tl isotopic variations have been observed in coal combustion, Zn smelting, and cement production.4,5 A positive linear relationship was revealed between the 1/Tl and Tl isotopic compositions for soils and geogenic backgrounds, indicating binary Tl mixing between the two dominant reservoirs.4,5 These findings indicate that Tl isotopic compositions can be B
DOI: 10.1021/acs.est.8b05282 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
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Environmental Science & Technology (BJ201709).The technical assistance from Xuwen Luo and Nuo Li is highly acknowledged.
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ABBREVIATIONS EPA Environmental Protection Agency EU European Union ICP-MS inductively coupled plasma mass spectrometry NIST National Institute of Standards and Technology
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REFERENCES
(1) Xiao, T. F.; Yang, F.; Li, S. H.; Zheng, B. S.; Ning, Z. P. Thallium pollution in China: A geo-environmental perspective. Sci. Total Environ. 2012, 421−422, 51−58. (2) Liu, J.; Luo, X. W.; Wang, J.; Xiao, T. F.; Chen, D. Y.; Sheng, G. D.; Yin, M. L.; Lippold, H.; Wang, C. L.; Chen, Y. H. Thallium contamination in arable soils and vegetables around a steel plantA newly-found significant source of Tl pollution in South China. Environ. Pollut. 2017, 224, 445−453. (3) Nielsen, S. G.; Rehkämper, M.; Norman, M. D.; Halliday, A. N.; Harrison, D. Thallium isotopic evidence for ferromanganese sediments in the mantle source of Hawaiian basalts. Nature 2006, 439, 314−317. (4) Kersten, M.; Xiao, T. F.; Kreissig, K.; Brett, A.; Coles, B. J.; Rehkämper, M. Tracing anthropogenic thallium in soil using stable isotope compositions. Environ. Sci. Technol. 2014, 48 (16), 9030− 9036. (5) Grösslová, Z.; Vaněk, A.; Oborná, V.; Mihaljevič, M.; Ettler, V.; Trubač, J.; Drahota, P.; Penížek, V.; Pavlů, L.; Sracek, O.; Kříbek, B.; Voegelin, A.; Göttlicher, J.; Ondřej, D.; Tejnecký, V.; Houška, J.; Mapani, B.; Zádorová, T. Thallium contamination of desert soil in namibia: chemical, mineralogical and isotopic insights. Environ. Pollut. 2018, 239, 272−280.
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DOI: 10.1021/acs.est.8b05282 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
