Study On Total Mercury Concentration And Mercury Isotopic Fractionation Of Water And Sediment In Jiulongjiang Estuary

Mercury has strong biological toxicity and environmental mercury pollution seriously threatens human health.Therefore,Hg has been listed as a priority pollutant by the World Health Organization.Jiulongjiang is the largest river in the south of Fujian Province,providing an important drinking water source to cities of Xiamen and Zhangzhou.Mercury pollution in Jiulongjiang area has been attracting great attention.In this study,the distribution characteristics and pollution sources of mercury in different environmental matrixes of Jiulongjiang Estuary were studied using methods of table mercury isotope analysis and traditional analysis.The main contents and results are as follows:(1)From 2017 to 2019,surface water samples and surface sediment samples of Jiulongjiang Estuary were collected in six cruises during wet and dry seasons.Total mercury(THg),mercury isotope composition of samples and other environmental parameters were measured to analyze the distribution characteristics and sources of mercury.The results show that THg in surface water was positively correlated with salinity,but not with pH,temperature and dissolved oxygen.THgs in surface water at wet season were higher than those at dry season,while in surface sediment at wet season were similar to those at dry season.THgs in surface water and surface sediment at different sites were closely related to factors of nearby environment.There was no significant difference between δ202Hg on surface sediment in wet season and dry season.The MIF in surface water at wet season was mainly caused by the photoreduction of mercury,while the MIF in surface sediment at dry season was produced by the deposition of mercury in surface water after photoreduction.The results show that mercury pollution in the surface sediments is mainly resulted from human activities.(2)On April 29,2019,core sediments of tidal flat of Longhai,Jiulongjiang Estuary were collected to determine THgs and mercury isotopic fractionation,for analyzing distribution characteristics of mercury in the tidal flat and impact of human sources.It is found that THgs in the mangrove sediment was significantly higher than those in the bare flat.The Muller index method was used to evaluate the impact risk of THg in core sediments.The results show that the mangrove sediments had moderate mercury pollution,while the bare flat sediments outside the mangrove forest had slight mercury pollution.Therefore,attention and control effort should be paid.The δ202Hgs of the core sediment in bare flat were more positive than those in the mangrove forest,indicating that more mercury pollution sources were introduced into bare flat due to human activities.In addition,the δ202Hg and Δ199Hg of core sediments in tidal flat were more negative than those in surface waters affected by tide in estuary.The ratios of Δ99Hg/Δ201　Hg in the sediments of mangrove and bare flat were different,indicating different MIF mechanism.The mangrove sediment had a slightly positiveΔ200Hg，which was supposed to be resulted from atmospheric deposition.