Variations in the isotopic composition of stable mercury isotopes in typical mangrove plants of the Jiulong estuary, SE China

Sun, Lumin; Lu, Bingyan; Yuan, Dongxing; Hao, Wenbo; Zheng, Ying

Variations in the isotopic composition of stable mercury isotopes in typical mangrove plants of the Jiulong estuary, SE China

2017

Sun, Lumin | Lu, Bingyan | Yuan, Dongxing | Hao, Wenbo | Zheng, Ying

Variations in the composition of stable isotopes of mercury contained in tissues (root, stem, leaf, and hypocotyl or flower) of three typical mangrove plants (Kandelia candel, Aegiceras corniculata, and Bruguiera gymnorhiza), collected from the mangrove wetland of Jiulong estuary, SE China, were used to investigate the sources and transformation of mercury in the mangrove plants. Tissue samples from the plants were digested and mercury in the solution was pre-concentrated with purge-trap method and then analyzed by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). The results showed that the mass dependent fractionation (MDF) of mercury ranged from −2.67 to −0.87 ‰ for δ ²⁰²Hg while the mass independent fractionation (MIF) of mercury isotopes ranged from −0.16 to 0.09 and −0.19 to 0.05 ‰ for Δ¹⁹⁹Hg and Δ²⁰¹Hg, respectively, relative to the standard NIST SRM 3133. The ratio of Δ¹⁹⁹Hg/Δ²⁰¹Hg was 0.991, indicating that the mercury had been photo-reduced before being accumulated in mangrove plants. Analyses of the data from MIF studies revealed that the major portion of the mercury measured in leaves (∼90 %) originated from the atmosphere while the source of over half of the mercury present in roots was the surficial sediment. This study, the first of its kind investigating the variations in isotopic composition of mercury in the tissues of mangrove plants, could be helpful to identify the source of mercury contamination in mangroves and understand the biogeochemical cycle of mercury in the estuarine mangrove wetlands.

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