Assessing Environmental Fate of β‑HCH in Asian Soil and Association with Environmental Factors Yue Xu, †,‡ Chongguo Tian, †, * Jianmin Ma, § Gan Zhang, ‡ Yi-Fan Li, § Lili Ming, ‡ Jun Li, ‡ Yingjun Chen, † and Jianhui Tang † † Laboratory of Coastal Zone Environmental Processes, Yantai Institute of Coastal Zone Research(YIC), Chinese Academy of Sciences (CAS); Shandong Provincial Key Laboratory of Coastal Zone Environmental Processes, YICCAS, Yantai Shandong 264003, China ‡ State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, 510640, China § Air Quality Research Division, Science and Technology Branch, Environment Canada, 4905 Dufferin Street, Toronto, Ont, M3H 5T4, Canada * S Supporting Information ABSTRACT: Chinese Gridded Pesticide Emission and Residue Model was applied to simulate long-term environmental fate of β-HCH in Asia spanning 1948-2009. The model captured well the spatiotemporal variation of β-HCH soil concentrations across the model domain. β-HCH use in different areas within the model domain was simulated respectively to assess the influence of the different sources of β-HCH on its environment fate. A mass center of soil residue (MCSR) was introduced and used to explore environmental factors contributing to the spatiotemporal variation of β-HCH soil residue. Results demonstrate that the primary emission dominates β- HCH soil residues during the use of this pesticide. After phase-out of the pesticide in 1999, the change in β-HCH soil residues has been associated with the Asian summer monsoon, featured by northward displacement of the MCSR. The displacement from several major sources in China and northeastern Asia shows a downward trend at a 95% confidence level, largely caused by environmental degradation and northward delivery of β-HCH under cold condition in northern area. The MCSRs away from the India and southern and southeastern Asia sources show a rapid northward displacement at a 99% confidence level, featuring the cold trapping effect of the Tibetan Plateau. ■ INTRODUCTION Technical hexachlorocyclohexane (HCH) was one of the most widely used pesticides in the world during the second half of the 20th century. During this period, about 10 million tons of the pesticide were released into the environment. 1 Technical HCH is a mixture of several isomers in the proportions α: 60- 70%, β:5-12%, γ: 10-12%, δ:6-10%, and ε:3-4%. 2 All isomers of HCH are characterized by environmental persistence, toxicity, potential for bioaccumulation and long- range transport. 3 Due to increasing concern on environmental contamination, technical HCH has been phased-out or banned worldwide before the 2000s. 4 In 2009, α-HCH, β-HCH, and γ- HCH were added to Annex A of the Stockholm Convention on Persistent Organic Pollutants (POPs) with no exemptions for ongoing production. Asia has been identified as a main source region of technical HCH in the world. China, the Former Soviet Union, and India together were estimated to consume about 75% of global total usage of the pesticide. 4 Although the use of technical HCH was discontinued in these countries and regions over 10 years ago, the environmental levels of HCH isomers were still high, 5,6 and posed a significant impact on ecosystems. 7 Presently, β-HCH is the predominant isomer in the environment 8 and human body 7 because of its resistance to microbial degradation and strong potential to bioaccumulate. 9 Like other POPs, partitioning and exchange of β-HCH among environmental matrices are strongly affected by temperature. 10,11 The Tibetan Plateau, located in the center of Asia, is the highest and biggest plateau on Earth. The low temperature plays a very important role in regional cycling and distribution of POPs in the plateau as a result of the cold trapping effect. 12 Previous studies have demonstrated that HCH contamination in the Tibetan Plateau was largely attributed to the emission from Indian sources. 13,14 In addition, the Asian monsoon system, including Indian and East Asia monsoon subsystems, as an important large-scale atmospheric circulation system, has also been found to dominate Received: May 21, 2012 Revised: August 7, 2012 Accepted: August 13, 2012 Published: August 13, 2012 Article pubs.acs.org/est © 2012 American Chemical Society 9525 dx.doi.org/10.1021/es302017e | Environ. Sci. Technol. 2012, 46, 9525-9532