Study On The Fate Of Persistent Organic Pollutants And Its Interaction With Phytoplanktons In Eutrophic Lake

With the development of industrialization,the lakes in China are faced with growing problems of eutrophication and persistent organic pollutants(POPs).Because of the high lipophilicity of POPs,they can easily be absorbed and degraded by phytoplankton.In this paper,Taihu Lake,a notorious eutrophic lake has been taken as research region to determine occurance and partition of concentrations in different enviornment media of phenanthrene(Phe)and dichlorodiphenyltrichloroethane(DDT).Moreover,effects on transport and bioaccumulation of POPs in eutrophic lakes by phytoplankton have been investigated.Furtherly,four typical algaes of eutrophic lakes including Microcystis aeruginosa,Cryptomons ovata,Cyclotella and Scenedesmus obliquus as well as two target compounds including were selected as study materials to indicate interactions between POPs and different phytoplankton species.In laboratory exposure experiments,physiological reactions of phytoplanktons exposed in POPs and adsorption and degradation process of POPs by different phytoplankton species was studied.The potential effects of phytoplankton on the adsorption and degradation of POPs was illustrated.Several important results were concluded as follows:(1)Phe and DDT as well as its metabolites,DDE and DDD,were detected in different environment medium.The Phe concentrations in waters,sediments and phytoplanktons are 24.36-72.58ng/L,27.54-92.12ng/g dw and 74.35-919.76 ng/g dw,respectively.The DDTs concentrations in waters,sediments and phytoplanktons are 0.25-2.27 ng/L,0.93-6.36ng/g dw and 1.39-19.08 ng/g dw,respectively.Moreover,DDT and its metabolites was easier absorbed on the phytoplanktons and sediments than Phe by calculating the fraction of POPs bounded to phytoplanktons(?)and Water-sediment distribution coefficient(Koc).(2)Redundancy anlaysis(RDA)showed absorption by phytoplankton would change the equilibrium partition of contaminants between air and water because of PAHs and OCPs were semivolatile,and finally the air-water exchange flux would change to cause seasonal difference for POP contents detected in water column due to different phytoplankton species.While for surface sediments,observed results indicated both Phe and DDT and its metabolites were mainly from the decayed phytoplankton.(3)Laboratory exposure experiments conducted with four different typical phytoplankton species indicated that Phe and DDT can be absorbed on four algaes influenced by specific surface area and lipid content.The fast adsorbent concentration of Phe and DDT of Microcystis aeruginosa and Scenedesmus obliquus were higher than the other two phytoplanktons because of larger specific surface area.However,the concentrations of Phe and DDT adsorbed on Cryptomons ovata and Cyclotella were higher than Microcystis aeruginosa and Scenedesmus obliquus because of higher adsorption capacity.(4)targeted contaminants could be degraded by four typical algaes,and Phe was easier to remove than DDT.The biodegradability of Phe and DDT by Scenedesmus obliquus was highest,with the removal rate of 64.2%± 1.9%and 37.6±2.9%,respectively.While the lowest removal rate of Phe and DDT was found by Micocystis aeruginosa(48.1 ± 1.5%and 19.9%±2.8%,respectively).(5)Phe of 1000ng/L and DDT of 200ng/L stimulated growth of phytoplankton.After a short period of exposure to pollutants,the cell density was increased rapidly and the cell activities were increased.Phenanthrene(Phe)had a better positive influence on the growth of phytoplankton than dichlorodiphenyltrichloroethane(DDT).Cyclotella reproduced more rapidly than Microcystis aeruginosa and Cryptomons ovata under the same pesticide concentration,while Scenedesmus obliquus reproduced slowly.In addition,POPs cooperating with nutrients stimulate growth of phytoplankton,especially Micrcystis aeruginosa by RD A between phytoplanktons and environment factors.