Effect Of Dissolved Organic Matter On The Change Of Mercury Form In Fish Culture Area

Consumption of Hg-contaminated maricultural products has been regarded as one of the major Hg exposure pathways to human body.It is of great significance to investigate the environmental geochemistry of Hg in maricultural zone due to the fact that the situation of marine pollution caused by Hg is getting worse.Many studies have demonstrated that the dissolved organic matter(DOM)plays an important role in governing the behavior of Hg in the aquatic environment.However,influence of a large quantity input of organic matters,which enter the aquaculture zone from both interior and exterior sources,on the existing forms and transformation of Hg,has not been systematically studied yet.As a matter of fact,there are a variety of DOM sources in the sediment.It leads to the great difference of DOM from different sources in terms of structure and chemical characteristics.Thus,the influence of DOM on Hg speciation is difficult to evaluate at whole level.It is therefore necessary to disclose the effects of DOM on Hg speciation change from a more microscopic view,such as the structure and functional group of subunits.In this study,the fecal materials collected from Daishan,Zhoushan City were isolated via a tandem connection of XAD resin and cation-anion exchange resin.Six subunits of the DOM derived from the fecal materials were categorized and thereafter tested to reveal their roles in Hg methylation,in an attempt to explore the mechanisms behind.The major findings of this study are listed as below:1.The DOM isolated from the fish fecal materials were rich in the carboxyl,hydroxyl,methyl functional groups.The environmental factors may influence the interactions of this functional group and cause the variation of microscopic structure and effects on the Hg methylation during different decomposition intervals.DOM showed a significant influence on the Hg methylation.However,the effects were not consistent and remained controversial.It is therefore a must to further investigate at a more microscopic level.2.The subunits of the DOM isolated from fish fecal materials by XAD and anion/cation resins were analyzed.The hydrophobic acids and alkalis were the major components,accounting for 72.7% of total weight.However,the hydrophilic subunits had more abundant functional groups comparing with hydrophobic ones.When the concentration of mercury in the solution is low,each DOM subcomponent has a higher conversion rate for methyl mercury(MeHg).3.The ratio of hydrophobic components to total amount of DOM declined with the decomposition progress of fish fecal materials,while the percentage of hydrophilic subunits increased from 8.0% at initial time to 28.1% gradually.In addition,the hydrophobic components showed an inhibitory effect to Hg methylation at the beginning,however,such an inhibitory effect weakened along the decomposition of fecal materials and ever turned to a positive effect to Hg methylation.On the contrary,the hydrophilic subunits exerted a promotive effect to the Hg methylation at the initial phase,especially the hydrophilic acids and neutral compounds.However,the positive effect declined and ever disappeared with the experiment lasting.