PAHs Pollution Characteristics And Ecological Risk In Aquatic Ecosystems Of Lanzhou Section Of The Yellow River

Polycyclic aromatic hydrocarbons(PAHs)have been categorized as persistent organic pollutants and widely existed in environments because of their resistance to degradation,low water solubility,and high lipid solubility.These properties enable PAHs to be readily accumulated in food chains,posing a potential risk to the ecological environment and human health.Located at the upper reaches of Yellow River,Lanzhou is an industrial city.Lanzhou section of the Yellow River supplies 70%of the water consumption for Lanzhou residents.Therefore,it is very important to gain knowledge for the PAHs concentration level and their ecological and health risk in water environment of Lanzhou section of the Yellow River.This study examined and assessed 16 priority U.S.EPA PAHs contaminations to water,sediment and fish(Triplophysa pappenheimi)from their samples collected at five cross sections across the Lanzhou Section of the Yellow River in December 2013.Based on the sampled data,the spatial distributions and biological magnification of 16 PAHs were also studied.The ratios of PAHs compounds and principal component analysis were used to identify the sources of PAHs in aquatic ecosystem.In addition,three methods including internationally accepted indicators of ecological risk assessment,risk quotient method,and probabilistic risk assessment were also employed to assess PAHs ecological risk in aquatic ecosystems of Lanzhou section of the Yellow River.Results and conclusions are summarized below:(1)PAHs pollution levels,composition,and spatial distribution characteristics in Yellow River aquatic ecosystem at Lanzhou Section ranged from 451.4 pg/L to 6733.6 pg/L(?16PAHs)with averaged concentration at 2165.9 pg/L.The highest water concentration was found at Xisha Bridge and lowest at Shichuan Bridge.Among 16 PAHs,2-4 ring PAHs had higher detection rate and concentration.Among them,e the highest concentration of PAHs was 3 ring Fla.Hence,Fla,together with BaP,can be selected as indicators of PAHs in water.Concentration of ?16PAHs in surface sediments ranged from 48.7 ?g/kg to 561.1 ?g/kg(d.w.)with averaged concentration at 239.2 ?pg/kg.The highest concentration was detected at Zhongshan Bridge and the lowest concentration at Bapanxia.All 16 PAHs have been detected.Ant at Zhongshan Bridge exhibited unusually high water concentration.It was found that the ratio of Fla/IcdP/BghiP can be regarded as a representative indicator for PAHs in surface sediments.?16PAHs levels in Triplophysa ranged from250.0 ?g/kg to 431.6 ?g/kg(fat weight)with average concentration at 349.5 ?g/kg which was lower than 4 ring PAHs and their detection rate in fish 2-3 ring PAHs based.(2)The spatial distribution of PAHs bioaccumulation in the aquatic ecosystem of the Lanzhou section of the Yellow River revealed some consistence between water and sediment concentrations of PAHs at each cross section.PAHs in water-sediment system showed an opposite spatial pattern where as their levels showed a positive correlation.BCF(bioaccumulation factor)was 2.04×106.Ant was if the highest BCF and the lowest one was found in BbF.The Biota-Sediment Accumulation Factor analysis showed that the PAHs bio-sediment bioaccumulation factor in surface sediments of the Yellow River in Lanzhou Triplophysa ranged from 109.3 to 8976.9 with the average at 2562.3.In general,each PAHs there were different BCFs and BSAFs.(3)Analytical study for source of PAHs in aquatic environment of the Yellow River in Lanzhou showed that PAHs in the Yellow River aquatic environment could be traced back to multiple sources,including natural and combustion sources,wood and other biomass sources,and burning oil source,etc..Among the five cross section along the river,PAHs detected in the Zhongshan Bridge water mainly came from oil pollution.The PAHs contaminations to the remaining river cross sections were attributable to mixed input sources.The PAHs levels in surface sediments in Zhongshan Bridge cross section showed less connection to natural sources whereas their levels in rest water cross section were attrbuted to both natural and anthropogenic sources,primarily including wood and other biomass burning,and coal burning.(4)By comparison with national standards,our results showed that,although the ?16PAHs in the Lanzhou section of the Yellow River exhibited low pollution levels,potential ecological risks of these contaminants should not be overlooked.To assess the risks of the aquatic species in the Lanzhou Section of the Yellow River,advantage and common species were selected in the present study Probabilistic risk assessment results showed that,under 50%confidence level,PAHs in aquatic ecosystems posed very low risk to aquatic species.Under 95%confidence level,the risk evaluation of individual PAHs congeners could resulted in a high exposure risk of more than 10%-60%organisms to BaP,Pyr,and Ant,more than 5%organisms to Fla,respectively.Total probabilistic risk of PAHs reached 64.72%.The combined effects of seven PAHs on aquatic ecosystems demonstrated that more than 60%aquatic organisms were under risks from their exposure to these PAHs.The mixed risks from multiple PAHs exceeded the risk from a single PAH congener.