Hg稳定同位素地球化学研究进展

近年来汞(Hg)稳定同位素研究进展显著。Hg具有七种稳定同位素。以往研究不但报道了Hg同位素质量分馏,也报道了Hg同位素非质量分馏,使Hg成为目前唯一在自然界中具有同位素非质量分馏的重金属元素。本文阐述了Hg同位素的研究背景,总结了Hg同位素分析方法和引起Hg同位素分馏的生物化学过程,介绍了地球各圈层样品中Hg同位素组成的国内外最新研究现状。而最新发现的大气降雨中异常的、呈季节性变化的偶数Hg同位素非质量分馏(Δ200 Hg),更开辟了Hg同位素研究的新领域。不同于奇数Hg同位素非质量分馏,偶数Hg同位素非质量分馏还未经任何实验验证,其分馏机理也完全不清楚,亟待深入研究。Hg可能的"三维"同位素体系(质量分馏、奇数以及偶数Hg同位素非质量分馏)的研究和应用将有希望为进一步认识Hg环境过程、生物累积、大尺度迁移以及全球性的生物地球化学循环提供更加丰富的信息,具有重要的科学意义。

Progress in the Study of Stable Hg Isotope Geochemistry

During recent decades,remarkable progress has been made in the study of Hg stable isotope geochemistry.Previous studies have reported both mass-dependent fractionation(MDF) and mass-independent fractionation(MIF) of Hg isotopes,especially MIF of odd Hg isotopes.Up to now,Hg is thus the only metal element that displays significant MIF of isotopes in the nature.This paper introduced the background of Hg isotope studies,and gave a summary of Hg isotope analysis methods(pre-concentration and isotope measurement),processes of Hg isotope fractionating and the isotopic compositions of Hg in different reservoirs on the Earth.Moreover,recent studies also have reported significant MIF of even Hg isotopes in precipitation.Neither laboratory experiment nor fieldwork has identified the mechanisms and processes inducing MIF of even Hg isotopes.Further study is thus needed to verify this observation and to get the best understanding of the mechanisms.The possible "three-dimension" of the Hg isotope system may provide new insight into all aspects of global bio-geochemical Hg cycle.