| Currently, the discharge of municipal sewage and industrial sewage, in particular, the not treated sewage have great harm to the environment. In the process of discharge of sewage adding different types of organic pollutants not only pollution levels increased, but also more complex. Urban sewage ditch muds are the sinks of dry and wet deposition of atmospheric and surface runoff. Therefore, finding out composition and distribution and sources of the organic pollutants of the urban sewage ditch is essential to the accurate evaluation of environment quality and effective control of environment pollution.In order to analyze the pollution level and sources of organic matter of sewage ditch in Lanzhou City, there were 23 surface samples were taken from the upper, middle and lower parts of 8 sewage ditch which are eventually into the Yellow River in Lanzhou City. In this paper, n-alkanes, isoprenoids, UCM, terpenoids and steroids, long chain alkyl benzenes were determined and analysed,and used its composition and parameters features to find the organic pollutants sources,and compared the difference of organic matters from the upper,middle and lower parts of sewage ditch,following statements were made:1.A series of saturated hydrocarbons including normal alkanes,isoprenoids,terpenoids, steranes, UCM,and long chain alkyl benzenes are detected in the mud of sewage ditch in Lanzhou City.2.The characteristics of n-alkanes, including Cmax, odd-even carbon predominance and maturity show that:the alkanes mainly from higer plants at the upper and middle parts of sewage ditch,but from phycomycetes at the lower.The alkanes mainly from higher plants at Qilihe, Shuimogou,Yuergou,the lower part of Paihonggou and the upper part of Luoguogou. The alkanes mainly from the mineral oil and its derivatives at the middle and lower parts of Luoguogou and the upper and middle parts of Paihonggou and the upper part of Lannigou.The former peak are from the mineral oil and its derivatives,the after peak are from higher plants at the middle and lower parts of Lannigou and Dashagou.The main peaks C3oap hopane reflects the oil pollution in mud samples from sewage ditch. gamma-n-wax/C3o hopane values 0.1-0.3.Ts/(Ts+Tm) and C3122S/(22S+22R) average 0.7 and 0.63 in the upper and middle parts of Siergou,which were higer than other samples.That was because Siergou is located in the oil and chemical-based integrated industrial zone.And other samples Ts/(Ts+Tm) values 0.3-0.54, C31 22S/(22S+22R) values 0.35-0.67.The composition and distribution characteristics of terpanes and steranes were reached or closed to equilibrium,which reflected the pollutants were derived from mineral oil or its derivatives.The regular steranesααα20RC27>ααα20RC29>ααα20RC28 inYuergou,Qilihe, Paihonggou,the upper and middle parts of Luoguogou,the middle and lower parts of Lannigou,which was reflected car engine oil pollution had greater impact.The regular steranesααα20RC29>ααα20RC27>ααα20RC28 in the upper part of Lannigou and Paihonggou,the middle and lower parts of Luoguogou,the lower part of Yuergou,which was reflected coal pollution had greater impact. The regular steranesααα20RC29>.ααα20RC28>ααα20RC27 in the upper part of Shuimogou,the middle part of Siergou,which were similar to the steranes from coal.3.The UCM drum bags were detacted at the samples fromQilihe,Yuergou, Lannigou,the upper and middle parts of Siergou and Luoguogou,the middle and lower parts of Paihonggou,and the lower part of Shuimogou.The distribution of UCM reflects the vehicle emissions and engine oil and its products of incomplete combusition.4.The long chain alkyl benzene and alkyl benzene isomers were detect in the mud of sewage ditch in Lanzhou City. The low abundance of long chain alkyl benzene was from Bacteria,algae and higher plants lipids.It was reflected the low organic matter in sewage ditch. The alkyl benzene isomers was from the detergent of sewage.
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