渔业养殖区溶解性有机质的来源、组成及其对汞甲基化的影响

The sources,composition and influence of dissolved organic matter on mercury methylation in fish aquaculture area

溶解性有机质(DOM)对水生环境中汞的赋存形态及转化过程具有极其重要的影响.但从更加微观的角度,如DOM的组成部分及其官能团特征等,却缺乏相关研究以阐明DOM影响汞形态转化的机制.为探究渔业养殖区来源于不同有机物(如残饵、鱼粪和底泥)的DOM各亚组分对水体中汞甲基化的影响,应用多级树脂联用技术,将渔业养殖区不同来源的DOM分离出6种亚组分,利用室内培养方式进行Hg^(2+)的甲基化试验.傅里叶红外光谱分析结果表明,DOM中含有各种不同的官能团.亲水性组分主要包含羟基、羧基等极性较强的官能团;疏水性组分则包含一些无极性或者弱极性官能团如甲基、亚甲基和酚羟基等.疏水性亚组分是DOM的主要组成成分,其中又以疏水性碱性物质(HOB)为最,在有机物腐解过程中一直占有最大的比重.总体而言,疏水性有机组分对汞甲基化的促进作用显著高于亲水性有机组分;这主要是因为亲水性有机组分含有大量的羧基、羟基等官能团,可以更好地与活性Hg^(2+)结合,降低甲基化反应的底物浓度,从而抑制甲基化发生.而疏水性组分对汞亲和性较弱,而且所含酚羟基以及还原性含硫基团等都可作为电子供体,从而促进汞甲基化的发生.从总体来说,在有机质腐解过程中,各种非同源有机质所形成的HOB对汞甲基化的促进作用不断增强.

It has been well documented that dissolved organic matters(DOMs)possess an important influence in the chemical species and transformation of mercury(Hg)in aquatic environment.However,at a more microcosmic level,there still exists a lack of information to illustrate the contribution of subunits and functional groups of DOMs towards Hg transformation mechanism.This study was conducted to investigate the influence of subunits of DOM from different sources on Hg methylation at aquaculture sites.A multiple-resin-combination technology was employed to separate the DOMs from different sources into six different subunits.Afterwards,an indoor incubation was setup to explore the DOMs'effect on the Hg methylation.The FTIR results show that the DOMs contained different functional groups,in which the ones with strong polarity such as carboxyl,hydroxyl were rich in the hydrophilic subunits,but non-polar or weakly polar groups such as methyl,methylene and phenolic hydroxyl groups were abundant in the hydrophobic subunits.Hydrophobic subunits were dominant components in DOMs.In addition,hydrophobic base(HOB)seemed to be the most overwhelming subunit during the whole decomposition process of organic matters in water.Generally,hydrophobic subunits exhibited a much stronger stimulatory effect on Hg methylation when compared to hydrophilic ones.It may be attributed to the fact that hydrophilic subunits contained more polar groups like carboxyl and hydroxyl which may form complexation with active Hg^(2+) ions in water,and therefore inhibit the methylation by lowering the reactant concentration.In contrast,hydrophobic subunits showed a much lower affinity to Hg ions.The phenolic hydroxyl as well as some reductive groups containing sulfur may serve as electron donors which are able to accelerate Hg methylation.In general,the stimulatory effect of HOB,derived from all organic matters,on the Hg methylation was enhanced with the lasting of decomposition of organic matters in water.