利用偏远地区湖泊沉积物揭示我国大气汞沉降的历史及来源

Mercury (Hg) is known as a global pollutant due to its long distance transportation in the atmosphere. Although China is regarded as the largest Hg emitter in the world nowadays, but the sharp increased, large quantities of Hg emissions is remained within the past 30 years since China's reform and opening up in late 1970's. While, for a long run, information on China's atmospheric Hg pollution caused by western countries, especially during the post-industrial time, are deficient, this making China a unfair and awkward status in the mercury diplomatic issues and the implementation of upcoming Hg treaty. In this study, one kind of archives samples, remote lake sediments with Hg input mainly through the atmosphere, will be collected from different lakes in remot areas of China. Through determination of the total Hg content, stable Hg isotope compositions, main and trace elements, as well as other related parameters in the samples, and combined with the dating technology of 210Pb and 14C, the variation and sources of Hg atmospheric deposition in China pre- and post- industrial period will be analyzed, contribution from outside and inside China will be quantified, and deposition from natural and anthropogenic sources could be distinguished. The range of Hg deposition variation due to natural factors such as global climate change in a long period (i.e. tens of hundred years) will also be investigated. This work will not only expand and penetrate the previous study, but with important scientific and realistic meaning.

汞是一种全球性污染物，可在大气中进行长距离迁移。虽然我国目前被认为是最大的汞排放国，但这种排放量可能仅是改革开放以来三十年内的事，对于较长的时间段，特别是工业革命以来，发达国家大量的汞排放对我国的大气汞污染了解甚少，这使我国在汞国际外交及未来汞公约履约方面缺少有力支持证据并面临被动局面。通过本研究，采集位于我国不同地区的偏远湖泊沉积物柱，利用这种天然的"历史档案"，通过总汞含量、汞同位素组成及其它主量、微量元素及相关参数的测定，结合210Pb及14C定年技术，分析我国大气汞沉降通量在工业革命前后的变化以及来源，确定国内外汞排放对中国大气汞污染的贡献份额，区分大气汞沉降的自然来源及人为来源，并研究历史较长时期内（如数百年到上千年尺度），全球气候变化等自然因素引起的汞沉降通量的波动范围。这项研究将深入及拓展以往的相关研究工作，也具有重要的学术价值和现实意义。

结合总汞、汞同位素组成及定年分析，对我国不同地区的11个湖泊沉积物的汞沉降通量及来源进行了研究。结果发现：工业革命以来，我国不同地区湖泊沉积物总汞含量总体都有所增加，偏远地区增加2~6倍，污染区最高达14倍；汞沉积通量在偏远地区增加4倍左右，而污染区增加50~100倍；汞同位素组成信息可以有效区分湖泊沉积物汞的来源，我国偏远地区湖泊沉积物中的汞主要来自大气汞的长距离传输、并通过降雨的方式输入，早期主要来源于北欧、北美地区的混汞法金、银提取以及汞冶炼排放的影响，后期国内生产活动的影响有所增加，汞同位素质量分馏和非质量分馏都呈现不同程度的增加；而我国南方湖泊沉积物更多的受国内生产活动的影响，如煤矿开采、燃煤、铅锌冶炼和土法炼金等活动，汞的非质量同位素组成（偏负，或接近为零）明显不同于北方偏远地区的湖泊（为正），更多的受人为活动、流域内土壤侵蚀、枯枝落叶等的影响。