| Mercury is a highly toxic global pollutant,and methylmercury is the most toxic of many mercury forms.Biofilm in natural water is a collection of microorganisms.It is rich in organic matter and can adhere to any exposed surface in water.It strongly changes the adsorption behavior of these surfaces.Biofilm can not only absorb mercury but also have an significant impact on the methylation process of mercury.There are many kinds of aquatic organisms that feed on biofilms.When aquatic organisms ingest biofilms containing mercury,they are enriched by food chains and eventually act on humans,which has a great impact on human health.Therefore,the study of the behavior of mercury in biofilms is very important.In this paper,the natural biofilms collected from the ocean and the biofilms artificially cultivated in natural seawater were used as research objects to study the adsorption and transformation behavior of mercury in biofilms.The results are as follows:1.Surface seawater,sediments and biofilm samples from eight stations nearshore of Dalian in the Yellow Sea were collected.The contents and distribution of THg(total mercury)and MeHg(methylmercury)in these three environmental medium were studied.And compare the mercury content of these three environmental medium.The results are as follows:The average values of THg and MeHg in seawater are 31.12 ng/L and 0.43 ng/L,and the average value of%MeHg(methylation ratio)is 1.10%.The average values of THg and MeHg in the sediment are 169 ng/g and 0.41 ng/g,and the average MeHg is 0.63%.The average values of THg and MeHg in the biofilm are 180 ng/g and 1.0 ng/g,and the average value of%MeHg is1.83%.The highest mercury content in seawater,sediments and biofilms appear at station 2,which is associated with long-term industrial pollution.By comparison,the total mercury and methylmercury content in seawater are much lower than those in sediments and biofilms,and the total mercury content in sediments and biofilms is similar,while the methylmercury content and methylation ratio in biofilms are larger than those in sediments.2.The marine biofilm was artificially cultured in the laboratory and adsorption experiments on mercury were carried out in order to explore the adsorption characteristics of mercury by biofilms in natural seawater.The thermodynamics and kinetics of mercury adsorption by biofilms were studied,and the effects of pH and dissolved oxygen on mercury adsorption were also discussed,the results are as follows:The reaction rate of biofilm and mercury is faster firstly and then stabilizes with time;With the increase of pH,the adsorption of mercury on biofilm rises at first and then decreases,when pH is 8,the adsorption amount reaches the maximum;With the increase of dissolved oxygen,the adsorption amount of mercury by biofilm gradually increased.When the dissolved oxygen was 8 mg/L,the adsorption amount was the largest.The Langmuir adsorption isotherm can accurately describe the adsorption process of mercury by biofilm.The adsorption kinetics accords with the quasi-second-order kinetic model,and the correlation coefficient is R~2=0.99042.3.The artificially cultured marine biofilm was used to investigate the methylation of mercury in low dissolved oxygen and high dissolved oxygen.The results are as follows:methylmercury in biofilms is mainly produced by methylation of mercury,indicating that biofilms have a positive effect on the methylation of mercury.As time goes by,the methylation ratio in the biofilm under high dissolved oxygen first remained unchanged and then decreased.Under low dissolved oxygen,the methylation ratio in the biofilm decreased first and then increased.After 12 days from the start of the experiment,the methylation ratio of biofilm under low dissolved oxygen condition was higher than that under high dissolved oxygen condition. |
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