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联合国环境规划署《2013年全球汞评估报告》指出:中国是全球汞(Hg)的主要排放国,总排放量为全球的1/3,亚洲的3/4。表明在中国开展汞的生物地球化学研究对人体健康和生态安全具有重要意义[1]。湖泊水库等水体中的汞主要来自河流输入和大气沉降,甲基汞(MeHg)则来源于水体汞的甲基化或沉积物中MeHg的释放[2],通过生物富集作用和食物链传递的生物放大作用,最终在人体内积累,对人类安全危害极大。丁之勇等[3]发现:中国31个湖泊沉积物中汞的平均质量分数为0.076 mg·kg−1;多个湖泊沉积物中汞的地累积指数达到中度或重度污染,潜在生态风险指数和平均污染程度仅次于镉(Cd)。张杰等[4]发现:太湖流域河流表层沉积物中汞的平均质量分数为0.109 mg·kg−1,超过背景值的采样点占47.87%,潜在生态风险评价处于中等或以上。近年来中国湖泊富营养化较为普遍,藻华时有发生,对湖泊水生生态系统造成极大威胁。溶解性有机质(DOM)是水生生态系统中水体天然有机质的主要成分(占97.1%)[5],通常指能通过0.10~0.70 μm滤膜,包含不同结构、分子量的碳基有机化合物,包括单糖、氨基酸等小分子化合物和蛋白质、腐殖质等大分子化合物。随着藻类暴发性增长,大量初级生产力进入[6],水体中DOM成分随之发生变化。如河流河口的硅藻Bacillariophyta藻华可显著增加DOM中碳水化合物的相对含量[7],类蛋白质荧光组分的峰强变化规律与各浮游藻类密度呈显著相关(r>0.80)[8]。一般认为,藻类正常生长的分泌物和降解的死亡藻体[9]都会造成沉积物中有机质的异常积累,从而改变水质参数,影响化合物形态的转化。DOM的—CH3、—CH2、—OH、—COOH、—C=O、—NH2等多种活性官能团可作为天然的载体与配体,与汞离子(Hg2+)发生氧化还原、络合、螯合、沉淀等一系列反应,从而影响水环境中汞元素的赋存形态、迁移性、溶解性以及最终归趋[10]。此外,DOM还会改变沉积物的氧化还原电位(Eh)和pH[11]、微生物种群等[12]环境因子,间接影响汞的形态转化。目前关于DOM影响汞甲基化的观点仍存在着较大分歧。有学者认为:DOM所含的还原态硫官能团能对汞产生络合作用,抑制其生物甲基化过程;也有研究者发现:较小的有机质会促进Hg的生物甲基化[13],DOM可以直接或在金属离子催化作用下参与非生物甲基化过程[14]。有鉴于水体中DOM来源的复杂性及其化学结构与性质的差异性,在总量水平上研究其对汞的影响难以形成定论。因此,有必要从更微观的角度阐明DOM对汞形态转化影响的作用机制。根据极性和电荷特性,DOM可分为6个成分,即疏水性的碱性、酸性和中性DOM以及亲水性的碱性、酸性和中性DOM[15]。水体富营养化和藻华使得藻体腐解过程产生的有机物成为水环境中DOM的重要来源。本研究通过室内模拟实验,对不同腐解阶段的藻类DOM进行逐步分离,取得6个亲水和疏水性亚组分,系统研究这些亚组分对汞甲基化的影响,以期丰富淡水环境中汞的生物地球化学理论,为汞污染的控制和降低汞污染健康风险提供科学依据。
Influence of algal derived dissolved organic matter on mercury methylation in water
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摘要:
目的 探究藻源溶解性有机质(DOM)各亚组分在不同腐解时间、不同汞(Hg2+)质量浓度下对水体中汞甲基化的影响。 方法 应用树脂串联技术分离藻体DOM的6种亚组分,利用室内培养方式进行Hg2+的甲基化试验。 结果 藻类DOM主要由羟基、烃基和芳环C=C等官能团组成;未经腐解的DOM各亚组分中,疏水性有机组分对汞甲基化的影响高于亲水性有机组分;随腐解时间延长,DOM官能团逐渐减少,疏水性有机组分对汞甲基化的影响表现为先降低后升高;亲水性有机组分抑制汞甲基化。 结论 DOM相对含量的升高抑制了汞的甲基化,DOM降解后,释放出来的Hg2+被微生物重新利用,甲基化程度加剧。图3参24 -
关键词:
- 汞 /
- 溶解性有机质(DOM) /
- 甲基化 /
- 有机质亚组分 /
- 藻类
Abstract:Objective To determine the effects of subcomponents of algae dissolved organic matter (DOM) on mercury methylation at different decomposition intervals and different Hg2+ concentrations. Method Six subcomponents of the DOM derived from the algae through a tandem connection of resin, and then conducted simulation experiments separately. Result Algae DOM was mainly composed of hydroxyl group, alkyl group and C=C of aromatic hydrocarbon, etc. Different subcomponents of DOM before decomposition, the influence of hydrophobic component on mercury methylation was significantly stronger than that of hydrophilic component. With the progress of algal decomposition, the relative content of functional groups was gradually decreasing while the influence of hydrophobic components on Hg methylation first weakened and then enhanced during the decomposition process and hydrophilic component can inhibit Hg methylation. Conclusion The increase in relative content of DOM results in the inhibition of Hg methylation. After the decomposition of DOM, the Hg2+ released got methylated by bacteria again, which helped promote the degree of methylation. [Ch, 3 fig. 24 ref.] -
Key words:
- mercury /
- dissolved organic matter /
- methylation /
- DOM subcomponents /
- algae
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链接本文:
https://zlxb.zafu.edu.cn/article/doi/10.11833/j.issn.2095-0756.20200146