渔业养殖区藻源溶解性有机质性质特征对汞甲基化影响

Characteristics of algae dissolved organic matter composition in coastal fishery farming area and its effect on mercury methylation

溶解性有机质(dissolved organic matter,DOM)是水生生态系统中的重要成分,能够显著影响汞的甲基化等形态变化过程.以近岸渔业养殖区藻源DOM为研究对象,运用傅里叶变换红外光谱和三维荧光光谱技术,对其结构特征进行表征;并选取总有机碳浓度TOC_(DOM)=10 mg·L^(-1)(DOM_(10))和TOC_(DOM)=50 mg·L^(-1)(DOM_(50))两种水平藻源DOM提取液,分析其在不同汞浓度条件下对汞甲基化过程的影响.结果表明,藻源DOM主要由类蛋白和类腐殖质组分组成,其中前者含量较高,疏水及芳香组分含量较低;红外光谱显示藻源DOM中含有—OH、—CH3、—CH2、芳香性C=C等官能团.甲基化实验表明,在溶液中DOM含量相对较少时(DOM:Hg浓度比≤15625),DOM表现出抑制汞甲基化的趋势,而当溶液中DOM含量逐渐升高(DOM:Hg浓度比>15625),DOM可以显著促进水体中汞向甲基汞的转化.藻源DOM既能作为碳氮来源提高微生物活性,为汞的甲基化提供甲基供体,又可以与溶液中Hg^(2+)发生络合,从而影响汞甲基化过程.在汞溶液浓度相对较低时,DOM对汞甲基化过程的影响主要表现为提供大量的甲基供体,同时作为微生物利用的底物,促进无机汞向甲基汞的转化,甲基汞转化率最高可达0.257%;但在高汞浓度条件下,DOM对汞的络合作用降低了无机汞的微生物可利用性,水体中甲基汞下降,表现出抑制作用.

Dissolved organic matter(DOM)is an essential component in aquatic ecosystems,significantly affecting mercury speciation changes such as the methylation process.In this study,DOM was leached from algae in the coastal fishery culture area.Fourier transform infrared spectroscopy and three-dimensional(3D)excitation-emission matrix(EEM)fluorescence spectroscopy were used to explore the composition and characteristics of algal DOM.The effect of DOM on the mercury methylation process was investigated using two DOM concentrations(according total organic carbon,TOC_(DOM)=10 mg·L^(-1)and TOC_(DOM)=50 mg·L^(-1)denoted as DOM_(10)and DOM_(50),respectively)and different mercury concentrations.The result shows that the algal DOM is mainly composed of protein-like and humic-like components which the former is higher.DOM has less aromaticity and hydrophobicity.The algal DOM contains—OH groups,—CH3and—CH2groups,C=C in aromatic structure,and other functional groups.DOM can inhibit mercury methylation in a lower content(DOM:Hg≤15625)while it significantly promote the conversion of mercury to methylmercury in solution as the content gradually increases(DOM:Hg>15625).It could promote mercury methylation by providing methyl donors or as the resource of C and N to improve microbial activity.In contrast,it can also be complex with Hg^(2+)during their reaction process and further inhibit mercury methylation.At lower mercury concentrations DOM mainly provides a large amount of methyl donors and as a substrate for microbial to enhance the methylation process,the methylmercury conversion rate is up to 0.257%.However,DOM reduced bioavailability of inorganic mercury at higher mercury concentration and showing an inhibitory effect as for the complexation mechanism.