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Reflection of stereoselectivity during the uptake and acropetal translocation of chiral PCBs in plants in the presence of copper Shaorui Wang, Chunling Luo, Dayi Zhang, Yan Wang, mengke song, Zhiqiang Yu, Yu-jie Wang, and Gan Zhang Environ. Sci. Technol., Just Accepted Manuscript • Publication Date (Web): 02 Nov 2017 Downloaded from http://pubs.acs.org on November 2, 2017
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Environmental Science & Technology
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Reflection of stereoselectivity during the uptake and acropetal translocation of
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chiral PCBs in plants in the presence of copper
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Shaorui Wanga, Chunling Luoa,b*, Dayi Zhangc, Yan Wangd, Mengke Songb, Zhiqiang
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Yua, Yujie Wange, Gan Zhanga
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a
Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
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b
College of Natural Resources and Environment, South China Agricultural University, Guangzhou,
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510642, China
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c
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School of Environment, Tsinghua University, Beijing, 100086, China
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Key Laboratory of Industrial Ecology and Environmental Engineering (MOE), School of
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Environmental Science and Technology, Dalian University of Technology, Dalian 116024, China
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e
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Guangzhou, 510006, China
School of Environmental Science and Engineering, Guangdong University of Technology,
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*Author for correspondence: E-mail:
[email protected]; Tel.: +86-20-85290290; Fax:
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+86-20-85290706
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Abstract
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Plant uptake and acropetal translocation of polychlorinated biphenyls (PCBs) is a
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major concern, with many uncertainties, especially when plants are exposed to
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co-existing PCBs and metals. Studying atropisomer selectivity behaviour is a
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well-proven method for identifying the biotransformation process of chiral PCBs in
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plants. This study investigated the uptake, translocation, and stereoselectivity of
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PCB95 and PCB136 (3 µg/L in hydroponics and 200 µg/kg in pot experiment) by the
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monocot corn and dicot sunflower after copper (Cu) exposure (50 µmol/L in
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hydroponics and 400 mg/kg in pot experiment). Cu exposure led to significantly
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increased PCBs accumulation in roots and enhanced their acropetal translocation from
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roots to shoots, attributed to Cu-induced root damage. In the absence of Cu, the
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first-eluting enantiomer of PCB95 and second-eluting enantiomer of PCB136 were
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preferentially enriched in the shoots and roots of both the monocot and the dicot, and
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the enantioselectivity of chiral PCBs was more pronounced in shoots than in roots. Cu
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exposure significantly reduced the stereoselectivity of PCB95 and PCB136 in the
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defective root system, implying that PCB95 and PCB136 uptake into roots after Cu
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exposure changed from active biotransformation to passive diffusion. Our findings
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suggest that the ecological risk of PCB95 and PCB136 uptake and accumulation in
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plants is underestimated at sites co-contaminated with metals and PCBs and, for the
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first time, reveal the mechanism associated with the uptake and biotransformation of
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chiral PCBs in plants after exposure to both heavy metals and chiral PCBs.
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Keywords: Chiral PCBs, Cu, Plant uptake, Acropetal translocation, Stereoselectivity
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Introduction
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Polychlorinated biphenyls (PCBs) are a well-known class of anthropogenic organic
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chemicals presented in a variety of industrial and commercial applications 1, 2. Among
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the 209 PCB congeners, 19 with three or four ortho-chlorine substituents are chiral,
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forming stable rotational isomers in the environment
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enantiomers of chiral PCBs are produced in equal proportions; however, in plants and
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animals, metabolic processes such as enzyme-mediated oxidation have been proven to
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target one stereoisomer preferentially, resulting in atropisomeric enrichment
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is an important index representing the biotransformation of chiral PCBs in different
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environmental matrices 6-8.
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The plant uptake, translocation, and enantioselectivity behaviour of chiral PCBs have
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been investigated with respect to the roles of plants in terrestrial ecosystems and risks
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to human health through food chain transfer
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concentration factor (TSCF), the ratio between a compound’s concentration in the
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xylem to that in the solution adjacent to the root, is commonly used to describe the
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relative ability of passive transport of organic compounds from roots to shoots.
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Normally, the TSCF is related to the octanol–water partition coefficient (Kow) of an
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organic compound 10, 11. Moderately hydrophobic organic compounds (0.5 < log Kow
