Distribution Characteristics And Risk Assessment Of Typical Persistent Toxic Substances In Xichuan Around Danjiangkou Reservoir

South-to-North Water Diversion Middle Line Project is a major strategic decisionof the State to conduct inter-basin water resources optimal allocation, which is a majorwater conservancy projects to ease the drought and water shortage in northern Chinaand ensure water supply safety. Recently, as the water source of the middle canal,Danjiangkou reservoir has draw great attention of the government and theenvironmental scientist, focusing on the agriculture nonpoint pollutant of nitrogen andphosphorus. However, data about the current contamination status with PTS which canseriously affect water quality and human health was very scarce in this area. So, it is ofgreat significance, and has great practical value on monitoring and analysis of PTS inDanjiangkou reservoir water and soil environment.The pollution of persistent organic pollutants in the soil from Xichuan submergedarea, surface water of Haoping River and runoff have been investigated in this article.15runoff ponds of three groups were built, and farmland soil samples, surface watersamples and two times runoff samples have been collected for experiments. Basing onthe data within two years, the distribution, level, types,sources and possible ecologicalrisk about heave metals、PAHs and OCPs were initially acquired in the reservoir area. Itwas found that:1.The contents of Hg、Cr、Pb、Cu、HCH and DDE in the soil of Xichuan meet thegrade III standard of the National Soil Environment Quality Standard(GB15618-1995).However, at part sampling sites，As、Cd and Ni only meet the grade Ⅲ standard，andBaa、Chr and Bbf that have the carcinogenicity were detected.2. The contents of heavy metals（Hg、Cr、Pb、Cu、Ni、Mn、Co）is higher infarmland、orchard and water fluctuating zone than in paddy and sdiment. The content ofHg is lower in water fluctuating zone，which is perhaps because Hg is easily formeddimethyl mercury in the condition of anaerobic in flooded or alkaline environment，which is insoluble，volatile、and easy to transform to mercury、methane and ethaneunder light.3. The contents of As and Hg meet the grade II standard，except Hg in the highflow period. Eleven of PAHs were detected in Haoping River; the mean value of PAHs and HCH contents in present study was lower slightly.4. Fourteen of PAHs were detected in the particles phase of rainfall runoff, twelvein water phase, and seven in the rain. Bap, which is of carcinogenicity, were detected inrunoff of cultivated land and orchard. The basic trend of PAHs、HCH and DDE in thesame use land type of rainfall runoff were:10～15°cultivated land＞5～10°cultivatedland＞0～5°cultivated land. It was also be found that the runoff volume and thecontents of PAHs、HCH、DDE in runoff increase with the slope.5. PAHs、HCH and DDE in the river of Xichuan mainly from the sediment release,but part of the PAHs also from the runoff and dry or wet atmosphere sedimentation.6. Ecological risk assessment show that: there is a low risk of heavy metals (Hg、As、Cr、Cd、Pb、Cu) in the soil of Xichuan submerged area. The mean value of PAHscontent in present study was lower, and has little negative ecological risk comparingwith ERL and ERM value of risk evaluation. α-HCH occasionally happen ecologicalrisk, but DEE at a rate of more than50%.