Speciation Of Trace Mercury And Its Interaction With Iron Sulfide In Aquatic Environment

Mercury and its compounds are an important class of persistent toxic metal pollutants in the natural environment,which are widely distributed in the atmosphere,water,soil,and other environmental media,and pose a great threat to the ecosystem and human life.With the rapid development of industry and economy,the problem of mercury pollution is becoming more and more prominent,which has attracted widespread attention.With the joint efforts of the United Nations Environment Programme and governments,the Minamata Convention,an international convention was adopted to limit mercury emissions in 2013.It is very important to study the transport and transformation processes of mercury species in the aquatic environment where toxic organomercury species are produced and bioaccumulated,which is of great significance for exploring potential environmental engineering methods to intervene the biogeochemical cycling of mercury for abatement and remediation of mercury pollution and the associated health risks.In this thesis,the enrichment/detection of methylmercury/divalent mercury and their interaction with iron minerals are studied as follows:?1?A new on-line solid-phase extraction-high performance liquid chromatography-inductively coupled plasma mass spectrometry?ICP-MS?technique was developed for the enrichment,separation,and detection of trace mercury in water.In this method,mercury species was fixed on C18 column pre-modified by dithizone,then eluted with 2-mercaptoethanol,and detected by ICP-MS.The high enrichment and sensitive detection of methylmercury and divalent mercury in the sample were successfully achieved.?2?The formation of hydroxyl radicals?·OH?mediated by reductive iron minerals in dark environment was investigated.We compared the hydroxyl radical formation from various reducing iron minerals at different oxygen conditions.The interactive effects of mackinawite?FeS?with environmental factors?pH,Cl^-,and dissolved organic matter?DOM??were investigated on the formation of hydroxyl radical.The results show that compared with other reducing iron minerals,FeS produces the most hydroxyl radicals under the same conditions,followed by reduced nontronite,siderite and pyrite.Structural Fe²⁺and dissolved O₂ play critical roles in·OH production from reduced iron minerals.·OH production increases with decreasing pH,and Cl^-has little effect on this process.More importantly,dissolved organic matter significantly enhances·OH production,especially under O₂ purging,highlighting the importance of this process in ambient environments.This sunlight-independent pathway in which·OH forms during oxidation of reduced iron minerals is helpful for understanding the transformation of mercury species,providing implications on processes for degradation of toxic methylmercury.?3?The adsorption behavior of methylmercury and divalent mercury on synthetic iron sulfide under anoxic conditions was simulated.It was found that methylmercury and divalent mercury could be quickly adsorbed by iron sulfide particles,and this adsorption may further reduce mobility,bioavailability,and transformation of mercury species,helping with exploration of natural and engineering processes for intervention of mercury biogeochemical cycling for pollution and risk mitigation.