Partition And Bioaccumulation Of PAHs In The Abiotic Environment And Food Web Of Dianshan Lake

Polycyclic aromatic hydrocarbons(PAHs)are important members of persistent organic pollutants(POPs)that are detrimental to both human health and the environment.In general,there have been many studies about sources of PAHs and associated health risk but there is hardly any research available mainly focusing on their multiphase migration,trophic transfer and bioaccumulation in both food web-containing muscles(food webm)and food web-containing whole bodies of organisms(food webwb).Dianshan Lake is an important urban lake of shanghai which is a source of water and fish,and place of recreational activities for local people.Polluted lakes with PAHs can greatly impact the ecological system and the health of people.This research work also has a worth of promoting eco-sustainable developments and cleaning strategies in the future.In this research,sediment,water,suspended particulate matter(SPM),plankton(zooplankton,phytoplankton)and bulk samples of 12 other species(yellow catfish,Japanese Spanish mackerel,Prussian carp,silver carp,common carp,whitebait,freshwater mussels,anchovy,freshwater snails,freshwater shrimp,sharpbelly,terrapin)were collected from the Dianshan Lake.To allocate different trophic levels to food web organisms,stable nitrogen isotopes were measured by Stable Isotope Ratio Mass Spectrometer connected with an elemental analyzer.All 16 PAHs compounds of water,sediment,SPM,and biota were analyzed by a gas chromatograph coupled with a mass spectrometer.A total organic carbon analyzer was used to measure total organic carbon(TOC).Multiphase partition coefficients(logks-w and logkp-w),trophic magnification factors(TMF),biota-sediment accumulation factors(BSAF),biota-SPM accumulation factors(BPAF),and bioconcentration factors(BCF)were applied to assess the PAHs transfer in the multiphase environment and accumulation in the food web.Based on the stable nitrogen isotope method four trophic levels were assigned from primary producers to tertiary consumers.The water phase was the least polluted phase compared to sediment and SPM.In water,sediment and SPM,the 16 PAHs concentrations were ranged from 178.08 to 394.83 ng/L,240.41 to 570.02 ng/g,and 3646.28 to 7010.81 ng/g,respectively.On the other hand,high molecular weight(HMW)compounds were the highest in sediment(74.4%)followed by SPM(59.1%)and water(55.9%).After transforming of partition coefficient values to logarithmic values,partition coefficient of sediment-water(Ks-w)values were ranged from 2.86(acenaphthylene)to 3.54(chrysene).Partition coefficient of SPM-water(logkp-w)values were ranged from 4.30(fluorene)to 4.51(benzo[ghi]perylene).This implied that logkp-w was a more influential factor than logks-w.The ratio of partition coefficients(Kp-w / Ks-w)revealed that the sediment was causing secondary pollution of PAHs in the SPM phase.Values of logkp-w and logks-w showed a strong significant relationship with the octanol water partition coefficient(logkow)(P < 0.05).This indicated logkow is one of the driving forces to determine the fate of PAHs in sediment-water-SPM system of Dianshan Lake.Mussel(filter-feeding organism)and yellow cat fish(piscivorous predator)had higher concentration of PAHs.Phytoplankton and zooplankton are important for transferring compounds from lower trophic levels to higher trophic levels.In TMF calculation,none of PAHs compounds showed values higher than 1,indicating clear biodilution of PAHs against trophic levels which,suggested strong metabolic transformation of such compounds.In food webm,nine PAHs congeners(acenaphthylene,acenaphthene,phenanthrene,fluoranthene,pyrene,chrysene,benzo[b]fluoranthene,benzo[k]fluoranthene,and benzo[ghi]perylene)showed significant trophic dilution,while six PAHs compounds(acenaphthylene,acenaphthene,fluorene,phenanthrene,fluoranthene,and pyrene)were significantly biodiluted in food webwb.The importance of whole bodies of organisms for studying the bio-transfer of organic compounds in the food web was established in this thesis.Because of two opposing scientific views for biomagnification and biodilution of PAHs in the food web,albeit based on a rather limited number of studies,our study investigated that there was parabolic behavior along with biodilution of PAHs compounds.Hepatobiliary system(such as gall bladder and liver)in the whole body was considered to have higher bioaccumulation potential of organic compounds than extrahepatic tissue.Among bioaccumulation factors,BCF was a more dominant factor that suggested organisms were accumulating more PAHs by exchanging with water.Bioaccumulations values calculated by BSAF were lower than 1 indicating accumulation of PAHs by organisms from sediment was not a major pathway of bioaccumulation in this food web.BPAF compared to BSAF was more important for bioaccumulation from solids.BCF,BSAF and BPAF values of low molecular weight(LMW)PAHs were generally higher than that of high molecular weight(HMW)PAHs.This trend could be explained by the octanol-water partition coefficient(logkow)of PAHs compounds and gut assimilation of PAHs compounds.Generally,LMW compounds have low logkow values and HMW compounds have high logkow values,which indicates the LMW PAHs are more likely to be distributed in water than HMW PAHs and therefore they are more likely to be bioaccumulated by organisms from water.Secondly,because of the low gut assimilation of HMW compounds by organisms than LMW compounds,the BCF,BSAF and BPAF values of HMWs are lower than the LMW PAHs.These findings indicated that LMW PAHs are more likely to be bioaccumulated from water,sediment and SPM by organisms than HMW PAHs in an urban lake.To evaluate the potential risks of PAHs in the environment,risk assessment models were applied by using risk quotient of negligible concentration(RQ(NCs))and risk quotient of maximum permissible concentration(RQ(MPCs)).The results showed that there were moderate and high ecological risks of PAHs in the water and SPM phase,respectively.However,there were almost no ecological risks of PAHs in the sediment phase.Moreover,the pollution level in organisms was in a safe range and the consumption of these organisms will not cause potential health risks to human beings.Considering water,there were potential carcinogenic risks caused only by benzo[a]pyrene and anthracene through water shower and bath over lifetime.