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

Abstract

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 Hg while the mass independent fractionation (MIF) of mercury isotopes ranged from -0.16 to 0.09 and -0.19 to 0.05 ‰ for ΔHg and ΔHg, respectively, relative to the standard NIST SRM 3133. The ratio of ΔHg/ΔHg 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.

Vegetation uptake of mercury and impacts on global cycling

“…There is strong evidence that in aboveground tissues most Hg originates from assimilation of atmospheric uptake (Figure 2) 52 . Many lines of evidence, including from flux measurements and stable Hg isotope analyses (Section 4), show that approximately 90% of Hg in leaves and needles is derived from atmospheric uptake of gaseous Hg(0) and that translocation of Hg from soils to aboveground tissues is limited [53][54][55][56][57][58][59][60][61][62][63][64] . One study estimated that 11% of Hg in a canopy originated from soils via xylem transport 65 , and another study showed less than 5% of soil solution root Hg uptake was translocated to shoots 45,59,66 .…”

Mercury Uptake, Accumulation, and Translocation in Roots of Subtropical Forest: Implications of Global Mercury Budget

“…Earlier studies have documented the pathways of foliage uptake of atmospheric Hg 0 and subsequent translocation into the aboveground woody biomass. ,, Foliage can take up atmospheric Hg 0 via stomata and nonstomata routes. ,, A portion of the incorporated Hg complexed with metallothionein then translocated from foliage to the aboveground woody biomass via phloem and xylem routes when accompanied with nutrient translocation in trees. ,, Given the absence of MIF during Hg translocation in vegetation, MIF signals are utilized for tracing Hg source apportionment in forest ecosystems. ,,, One earlier study found that the Δ 199 Hg and Δ 200 Hg values of the shallow roots were comparable to signatures of foliage and surface soils, indicating that Hg in shallow roots is derived from atmospheric Hg 0 depositions, but it could not distinguish whether the Hg direct translocation from foliage to root, or from litterfall Hg deposition into soils, is then uptaken by roots.…”

Mercury Isotopes in Shale Gas From Wufeng-Longmaxi Shale Formation of Sichuan Basin, Southern China: A Preliminary Investigation

“…Photoreaction is the main natural process leading to the mass-independent fractionation of mercury stable isotopes (Bergquist and Blum, 2007;Kwon et al, 2020), where mercury isotopes are essential in tracing mercury sources and geochemical processes. Many studies have been conducted on mercury isotopes in organic matter correlated to oil and gas, such as algae and phytoplankton (Perrot et al, 2012;Tsui et al, 2012), invertebrates (Blum et al, 2014), lake sediments, marine sediments (Feng et al, 2010;Ma et al, 2013), terrestrial plants (Sun et al, 2017;Wang et al, 2017), lichens (Carignan et al, 2009), peat (Enrico et al, 2017;Enrico et al, 2016;Shi et al, 2011), coal (Biswas et al, 2008;Lefticariu et al, 2011;Sun et al, 2016), and soil (Foucher et al, 2009;Yin et al, 2013). The Hg isotopic ratios show promise as a method for distinguishing different sources of natural gas.…”