Distribution And Risk Assessment Of Polycyclic Aromatic Hydrocarbons (PAHs) And Their Derivatives In Surface Water Of The Yangtze River

Polycyclic aromatic hydrocarbons（PAHs）are a type of persistent organic pollutants,which are commonly detected in aquatic environments,and some of their derivatives（SPAHs）have stronger carcinogenicity,mutagenicity and teratogenicity.At present,there are many related studies on the PAHs of a certain main stream section,tributary and estuary of the Yangtze River,but there is a lack of systematic research on the PAHs and SPAHs of the water bodies of the upper,middle and lower reaches of the Yangtze River.In this thesis,the distribution and sources of 19 polycyclic aromatic hydrocarbons and their 15 derivatives in surface water of the Yangtze River were studied during dry,wet,and normal periods,including Panzhihua,Yibin,Luzhou,Chongqing,Fuling,Three Gorges Reservoir,Yueyang,Wuhan,Jiujiang,and Nanjing sections.Besides,the risk levels and spatial-temporal differences of PAHs pollution were assessed.The results showed that the average concentrations of∑PAHs and∑SPAHs of the Yangtze River were respectively 173.8±11.6ng·L^-1and 372.9±507.2 ng·L^-1.For SPAHs,average concentrations of∑NPAHs（nitrated-PAHs）,∑MPAHs（methyl PAHs）,and∑OPAHs（oxygenated-PAHs）were respectively 327.0±498.8 ng·L^-1,26.5±5.4 ng·L^-1,and 19.4±11.0 ng·L^-1.There are 13 types of parent PAHs and 9 types of SPAHs with detection rates higher than 70%in all surface water samples of the Yangtze River in different periods.The concentration of PAHs and SPAHs in water is positively correlated with TOC overall,but has no significant correlation with flow velocity.The temporal and spatial distribution characteristics of PAHs and SPAHs in the waters of the Yangtze River indicate that the concentrations of PAHs and SPAHs in water bodies tends to increase from upstream to downstream,which may be caused by factors such as high population density in the downstream,more industrial activities,and more developed shipping.Combining molecular ratio method and principal component analysis（PCA）to identify the source of PAHs and SPAHs,the results show that incomplete combustion of biomass,fossils and liquid fuels is the main source of PAHs in the water bodies of the Yangtze River in different periods.Combustion sources and photochemical conversion were the main sources of SPAHs.Both SPAHs and PAHs mainly entered into water bodies through atmospheric deposition.To evaluate the health risks of PAHs and SPAHs in waters by using toxic equivalent factor method and lifetime carcinogenic risk incremental models（ILCRs）,the results show thatΣTEQ_{Ba P}（benzopyrene toxicity equivalent）has significant differences in different periods,so attention should be paid to the health risks caused by PAHs in dry periods and MPAHs in normal periods.The ILCRs of PAHs and SPAHs in the waters of the Yangtze River are all less than 1×10^-6（U.S.EPA standard）,indicating that the Yangtze River has no carcinogenic risk.The risk quotient method was used to assess the ecological risks of PAHs in water bodies,and the results show that the single PAHs of the Yangtze River are at a moderate risk,theΣ₁₆PAHs in the middle and lower reaches of the river are in a high-risk level,and the upper reaches of the water∑₁₆PAHs are in a medium-risk level.