中国科学院西双版纳热带植物园机构知识库

汞是生物体非必需、有毒有害的重金属，可以通过工业过程以单质态被排入大气，进而全球性分布，最终通过沉降造成环境污染。汞可以被生物富集，在潮湿和厌氧条件下被转化成更具有生物可利用性和神经毒性的甲基汞。传统观念认为水生的大型顶级捕食者面临汞暴露最大的风险，然而对陆生生态系统的了解较少。亚洲地区人为汞的排放量居世界之最，汞矿区农业种植区域居民汞的暴露途径是通过稻米而非鱼类等水产品。然而，在亚洲尚未有对汞是如何通过稻田生态系统传递进行全面的研究，也未有这一类型生态系统中的生物进行汞含量的报道，进而去了解这些生物的生存和繁殖是否受到环境汞污染的影响。
中国万山汞矿曾是亚洲第一大的汞矿，已于2001年政策性关闭。我们调查研究了贵州万山汞矿区稻田附近自然野生生态和距该汞矿区以西200公里的无汞矿冶炼活动的雷山县对照区生态中自由生活（放牧）的野生动物群落的汞含量。在研究中，我们测定了土壤、稻米和生物体（包括蚯蚓、水稻害虫、肉食性无脊椎动物、青蛙、蛇、鱼、鸣禽（夜莺）、猫头鹰、翠鸟和人发、血液等）的汞含量、甲基汞比例（甲基汞/总汞）以及稳定碳、氮同位素分析。对于不同种类生物，采样设计尽可能采集离万山矿区大型矿坑不同距离的生物样品，大部分采样工作于2014年进行，但我们还在2015年采集了水稻生长前期和接近收获期两个时期的无脊椎生物。论文主要研究内容，包括如下几部分：
第一部分主要研究汞在蚯蚓体内的富集。土壤和蚯蚓的总汞和甲基汞浓度随着远离采矿区而降低，但甲基汞占总汞的比例和蚯蚓的生物富集因子却随着距离增加呈现升高的现象。汞甲基化程度的增加和蚯蚓中甲基汞含量增加，可能是由于远离矿区的土壤酸性更II

强和有机质含量更高有关。在以沉降为主要汞源的雷山区域，淹水土壤尤其酸性稻田土壤中，蚯蚓对甲基汞的生物放大作用比之前国内外报道的数据结果更为显著。
第二部分主要研究汞在蜘蛛和蝗虫体内的富集。根据2014年数据，我们可以看出，与蚯蚓的情况相似，随着距废弃矿区距离的增加，蜘蛛和蝗虫体内的总汞和甲基汞逐渐降低，并具有统计学意义。大部分物种在远离矿区的地区甲基汞占总汞的百分比较高，而蝗虫体内甲基汞占总汞的比例在整个研究区域内差别不大。土壤中甲基汞占总汞的比率和这些无脊椎动物体内的甲基汞水平具有明显的相关性。通过对蜘蛛的稳定碳、氮同位素分析可以得出，处于较高营养级的物种体内甲基汞含量也较高。根据2015年两个季度的数据来看，土壤中总汞含量基本不变，但是在水稻即将成熟的时期，土壤甲基汞明显升高，进而导致在所有采样点，所有物种的甲基汞都有明显地季节性的增长。
第三部分主要研究研究汞在生态系统所有营养级水平生物体内及有机质中的富集特征。我们测定了土壤、水稻、38个动物样品（27个测定了甲基汞）和居民发样、胎盘和血液样品总汞和甲基汞含量。结果表明，总汞在生物体内富集特别是甲基汞，具有极强的生物放大特征，食虫鸟类羽毛中总汞含量最高，汞矿区对应鸟类总汞含量是国际报道影响鸟类繁殖阈值的15倍，而非矿区鸟类总汞含量亦达到了3倍。食谷类和食虫类的鸟中汞含量相当，表明水稻是汞暴露的重要来源。
我们的研究表明，亚洲部分地区的环境汞污染可能已经对生物种群健康产生了明显的影响，在一些敏感生态系统，如遍布亚洲的农业湿地，可能会导致生物多样性减少。未来评估汞的风险和更好的履行水俣公约，各国政府选用鸣禽进行共同的生物监测是有必要的。

Mercury is a heavy metal that is toxic to both humans and animals. It is emitted to the atmosphere through industrial processes and thereafter globally distributed; local pollution problems can also occur. Mercury bioaccumulates and under wet, suboxic conditions is chemically altered into methylmercury (MeHg), which is more biologically available. For this reason, traditionally it has been thought that large, top predators in aquatic ecosystems are most at risk; less is known about terrestrial ecosystems. Emissions are particularly high in Asia, and the route of exposure for humans in agricultural areas may be through rice, rather than fish. However, how mercury flows through natural wild ecosystems near rice paddies has not been fully explored in Asia, nor have the concentrations of mercury in organisms in such ecosystems been measured, to understand how their survival and reproduction might be affected.
We tested the mercury levels of free-ranging animal community nearby rice paddies in the Wanshan Mercury District, Guizhou Province, China, one of Asia’s largest mercury mines until its closure in 2001, and at a control site 200 km away, also in Guizhou, but with no history of mercury mining. We measured total mercury (THg) concentrations, and the percent methylated, in soil, rice, and a range of organisms, including earthworms, invertebrate rice pests, carnivorous invertebrates and frogs, snakes, fish, song birds, owls, kingfishers and humans. The sampling schemes for different taxa varied, but we attempted to sample organisms at a varying distances form the mines in Wanshan when possible. Most sampling occurred in 2014, but in 2015 we collected invertebrates at two different seasons: before the rice growing season, and close to harvest. At the most contaminated areas in Wanshan, we also collected samples for stable isotope analysis.
In the first project that focused on earthworms, THg and MeHg concentrations declined in soil and earthworms as distance increased from the mines, but the percentage of THg that was MeHg, and bioaccumulation factors in earthworms, increased over this gradient. This escalation in methylation and the incursion of MeHg into earthworms may be influenced by more acidic soil conditions and higher organic content further from the mines. In areas where the source of mercury is deposition, especially in water-logged and acidic rice paddy soil, earthworms may biomagnify MeHg more than was previously reported.
The second project focused on spiders and grasshoppers. Using the 2014 data, we saw a similar pattern as in earthworms, with the THg and MeHg concentrations in spiders and grasshoppers decreasing with increasing distance from the abandoned mines, and this pattern was statistically significant for all species. Patterns in the percentage of THg that was MeHg were complicated, with most species having a higher percentage methylation farther from the mines, IV

but grasshoppers showing a similar percentage of MeHg everywhere. There were strong correlations between soil THg/MeHg levels and invertebrate MeHg levels. Among the spiders, there was a tendency for those at higher trophic levels, as judged by stable isotopes, to have higher MeHg concentrations. For the 2015 two season data, THg concentrations in soil were stable during two seasons, but soil MeHg concentrations were significantly higher when rice was close to being mature. For all invertebrate species, and all sites, there was a strong seasonal increase in MeHg.
The third project had the widest taxonomic sampling, covering organisms at all trophic levels in this ecosystem. We measured THg and MeHg in soil, rice, 38 animal species (27 for MeHg), and humans. Our results confirm bioaccumulation of THg, and particularly MeHg, exhibiting exceptionally high trophic magnification slopes. Invertivorous songbirds accumulated the highest THg concentrations; at mining sites this was 15x the concentration reported to significantly impair their reproduction, and at non-mining sites it was 3x this level. High concentrations in specialist rice pests and in granivorous birds, as high as in piscivorous birds, suggest rice is a primary source of exposure.
Our findings suggest there could be significant population level health effects and consequent biodiversity loss in sensitive ecosystems, like agricultural wetlands, across Asia. Multinational biomonitoring with invertivorous songbirds is necessary for assessing this risk and for successful implementation of the Minamata Convention on Mercury.