Analysis Of Pollution And Research Of Risk Assessment Based On The Heavy Metals In Water Of The Three Gorges Reservoir(Section In The Main Urban Area Of Chongqing)

Heavy metals are common pollutants in the water environment with its inherent toxicity,persistence,irreversibility,concealment,bio-accumulation,and nondegradability.Heavy metals could be accumulated in nature.The heavy metals could be uptake by the growth of animals and plants from soil water and atmosphere,while migrated and transformed through the food chain and food net,and enter into the human body finally.These will cause serious physical consequences and even death for the human.The Three Gorges Reservoir(TGR)located in upstream region of the Yangtze River.As the important part of TGR,the main urban area of C hongqing is also one of area of both most rapid economic development and densely population in the Yangtze River Basin.It is of great significance for human health and the security and sustainable development of regional economy to study the pollution status of heavy metals in water.So far,contrastive study of heavy metals in the water between before and after impoundment is less,and the results of the paper can help people to understand the influence of impoundment to the maximum level of 175 m.To thoroughly investigate the pollution status of heavy metals in water in TGR(section in the main urban area of C hongqing),the content of heavy metals(Cr?C u?Zn?As?Cd?Pb?Se?Sb?Ba and N i)of water and suspended matter were measured.The main research methods were used to study six kinds of heavy metals(Cr?C u?Zn?As?Cd and Pb)with high content that analysis of spatial and temporal distribution,health risk assessment,index of geo-accumulation and potential ecological risk assessment.In this study,the pollution characteristics of heavy metals in the water of TGR(the main urban area of C hongqing)were analyzed more comprehensively,and provide theoretica l basis and data support for the prevention,control and treatment of heavy metal pollution in the TGR.The following are discoveries:(1)The results of dissolved heavy metals of water showed that,(a).The concentrations of Se?Sb?Ba and N i are far below than the standard value of he National Surface Water Environmental Quality Standards(GB3838-2002)I,and the concentrations of Cr?C u?As and Cd in the water of TGR reached the standard of the National Surface Water Environmental Q uality Standards(GB3838-2002)I,while the concentrations of Pb and Zn reached the standard of III.(b).The trends of different heavy metals concentrations with time are different in every sampling sites from 2015 to 2016.In general,the concentrations of Cr?C u?As and Cd showed a decreasing trend,while the concentration of Zn showed a rising trend in most sampling sites.In 2016,heavy metal pollution in C untan is more serious than other sites.(c).O n the whole,the total concentrations of dissolved heavy metals in water showed a rising trend from 2015 to 2016,and Zn is the largest contribution of heavy metals.(2)By combining previous research results and results of this paper,and analyzing,the result has been found that the concentrations of disso lved heavy metals(C r,Cu,As,Cd and Pb)showed a slight downward trend as a whole,except for Zn,from 2005 to 2016.Although the impoundment of TGR has different effects on different heavy metals,heavy metal pollution was reduced in general.(3)The results of aquatic environmental health risk assessment showed that the risk of the carcinogenic heavy metals was higher than the risk of the non-carcinogenic heavy metals at each sampling site in general.As posed the highest risk to human health in the TGR.Most of the sampling sites were polluted lightly by heavy metals,the water collected from the C untan has been seriously polluted by heavy metals in 2016,which posed a great threat to human health.(4)The results of heavy metals of suspended matter sho wed that,the highest content of heavy metals is Zn,followed by Cr.The total content of heavy metals decreased from upstream to downstream of Yangtze River in this study area.The index of geo-accumulation of heavy metals in suspended matter lay in the sequence Cr < C u < Pb < Zn < Cd < As,and the study area was not contaminated by Cr.As was highly enriched in suspended matter which the content of As has exceeded the intense contamination degree,even reached the level of extremely strong pollution.The results of potential ecological risk assessment showed that the total potential ecological risk index(RI)of six kinds of heavy metals was decreased from the upstream to downstream of the Yangtze River in this study area in turn,and the harm fell into a decline.The Cd of potential ecological risk index(ECd)made great contribution to the total potential ecological risk index(RI).Therefore,Cd is the main hazardous heavy metals in suspended matter in TGR(section in the main urban area of Chongqing).