The Role Of Typical Algae In Mercury Methylation In Karst Waters Of Guizhou Province

Algae is a primary producer of aquatic systems and is a key link in the entry of methylmercury?MeHg?into the aquatic food chain.In aquatic systems,fish rarely absorb mercury directly from water,mainly through food intake,while inorganic mercury is converted to MeHg,which is accumulated in algae cells by algae adsorption and enrichment of MeHg,thereby entering the aquatic food chain.Guizhou Baihua Lake,Hongfeng Lake and Ahahu Reservoir are typical karst water bodies.They are located in the global mercury mineralization zone.The mercury has a high background value of mercury,and the algae grows fast and has abundance.The typical algae in the basin was selected as the research object to study its role in mercury methylation,to elucidate the effect of algae cells on mercury methylation,to further understand the interaction between algae and mercury,and the environmental earth of mercury in karst water.Chemical behavior is very important.To this end,this study used typicalalgae-Chlorella ellipticus,Anabaena sp.,Aphanizomenon flosaquae and Microcystis aeruginosa as research objects,using indoor simulation experiments to explore different activities?living,dead?algae in natural light,darkness The effect of IHg methylation on the condition;at the same time,the water-air interface release characteristics of Hg⁰ in MeHg solution in the presence of algae and the adsorption characteristics of MeHg by algae were studied.The results showed that the four algae could grow in the presence of mercury at a concentration of 0.1-10?g/L,but the abundance of the four algae decreased with the increase of mercury concentration.The total amount of MeHg produced by Chlorella ellipticus at different concentrations of mercury was 8.536×10^-2-0.1564 ng,and the total amount of MeHg produced by Anabaena sp.under different mercury concentrations was3.758×10^-2-2.572 ng.The total amount of MeHg produced by Aphanizomenon flosaquae under different mercury concentrations was 0.1574-3.237 ng,and the total amount of MeHg produced by Microcystis aeruginosa under different mercury concentrations was 5.349×10^-2-8.524×10^-2 ng.During the reaction,the total amount of MeHg produced by the four algae under different mercury concentrations showed a downward trend.On the 5th day before the reaction,the total amount of MeHg produced by the living algae of the four algae was always higher than that of the dead algae.The total amount of MeHg produced by the dead algae on the 7th day increased rapidly,and finally higher than that of the living algae.The total amount of MeHg produced by Chlorella ellipticus,Aphanizomenon flosaquae,and Microcystis aeruginosa under natural light conditions decreased from 6.998 ng,2.074 ng,2.068 ng to 8.536×10^-2,0.2133ng,6.964×10^-2 ng,respectively.The total amount of MeHg produced under dark conditions changes little,and the overall appearance shows a decreasing trend.The total amount of MeHg produced by Anabaena sp.under natural light conditions and darkness increased from 1.821 ng and 0.5946 ng to 2.572 ng and1.577 ng,respectively,showing an overall growth trend.In the presence of four algae,Hg⁰ was produced in MeHg solution over time,but when the concentration of MeHg was too high?100 ng/L?,the presence of four algae inhibited the release of Hg⁰.In the presence of living algae and dead algae,Hg⁰ was produced in MeHg solution,and both living algae and dead algae inhibited the release of Hg⁰.The inhibitory effect of dead algae on Hg⁰ release was more obvious than that of living algae.The Hg⁰ release rate under natural light and dark conditions in the presence of Anabaena sp.was 3.495%and 2.583%,respectively,and the Hg⁰ release rate under natural light conditions was higher than that in dark conditions.WhenChlorella ellipticus,Aphanizomenon flosaquae,and Microcystis aeruginosa existed,the Hg⁰ release rates under natural light conditions were 2.121%,2.776%,and 1.383%,respectively.Under the dark conditions,the Hg⁰ release rates were 2.294%,1.069%,and 0.8696%,respectively.Both showed that the release rate of Hg⁰ was higher than the natural light condition under dark conditions.The four algae had good adsorption effect on MeHg.At 360min,the adsorption of MeHg by Chlorella ellipticus under different MeHg concentrations was 9.638-99.38 ng/L?living algae?and 8.12-91.34 ng/L?dead algae?,the adsorption of MeHg by Anabaena sp.under different MeHg concentrations was9.541-99.15 ng/L?living algae?and 7.563-92.18 ng/L?dead algae?,the adsorption of MeHg by Aphanizomenon flosaquae under different MeHg concentrations was 8.925-99.16 ng/L?living algae?and 8.374-90.89 ng/L?dead algae?,the adsorption of MeHg by Microcystis aeruginosa under different MeHg concentrations was 9.467-98.50 ng/L?living algae?and 7.586-94.02 ng/L?dead algae?.The equilibrium adsorption capacity of MeHg by four kinds of algae increased with the increase of the initial concentration of MeHg,and the adsorption amount of living algae was higher than that of dead algae.The kinetic adsorption process of methylmercury by the living algae of Chlorella ellipticus is in accordance with quasi-first-order and quasi-second-order kinetic models.The kinetic adsorption process of methylmercury by the dead algae of Chlorella ellipticus is more in line with quasi-second-order kinetic model.The kinetic adsorption of methylmercury by the living algae of Anabaena sp.fitted the quasi-second-order kinetic model.The kinetic adsorption process of methylmercury by the dead algae of Anabaena sp.accords with the quasi-first-order kinetic model.The kinetic adsorption process of methylmercury by the living algae and dead algae of Aphanizomenon flosaquae is in accordance with the quasi-first-order and quasi-second-order kinetic models.The kinetic adsorption of methylmercury by living algae of Microcystis aeruginosa accords with quasi-first-order and quasi-second-order kinetic models,while that of dead algae accords with quasi-second-order kinetic models.The adsorption of methylmercury by the living algae of Chlorella ellipticus was in accordance with the Freundlich isotherm adsorption model.The adsorption of methylmercury by the dead algae of Chlorella ellipticus conformed to the Langmuir isotherm adsorption model.The adsorption of methylmercury by the dead algae of Anabaena sp.was in accordance with the Freundlich isotherm adsorption model.The adsorption of methylmercury by the living algae of Aphanizomenon flosaquae was in accordance with the Freundlich isotherm adsorption model.The adsorption of methylmercury by the living and dead algae of Microcystis aeruginosa was in accordance with the Freundlich isotherm adsorption model.The four algae cell walls contain functional groups such as C-O and O-H,which can adsorb MeHg,and the four algae cells have larger specific surface area,which can provide more sites for the adsorption of MeHg.