Pollution Characteristics And Risk Assessment Of Heavy Metals In The Main Stream Of Lean River

Le’an River, where had a long history of mining wastewater pollution was selected as the study area in this dissertation. After investigation, we chose 22 sampling sections to test the total concentrations and forms of Cu、Zn、Pb、Cd、Cr and As in surface sediments. On the basis of each heavy metal’s spatial distribution characteristics, we traced their sources along the Le’an River, then used a variety of methods to conduct a comprehensive assessment of environmental pollution risk in sediments.The distribution characteristics of heavy metals in sediments was analyzed from two aspects, total concentrations and forms, respectively. The contents of sediment samples concentrated between 7.12-2964.87 mg/kg for Cu, 52.54-3008.20 mg/kg for Zn, 12.66-2023.99 mg/kg for Pb, 0.48-68.89 mg/kg for Cd, 20.06-466.56 mg/kg for Cr, 12.82-433.04 mg/kg for As, respectively. The high value areas of six kinds of elements were basically concentrated in the upstream and midstream regions,especially sections in Daicun, Hushan and Leping, where appeared a high concentration of each element more frequently; Based on sediment background values of Poyang Lake basin, the average enrichment degree of each element was in the decreasing order: Cu > Pb > Zn > Cd > As > Cr. From the aspect of elements’ forms,the distribution of the residue in six elements was similar to each other, basically kept a relatively low value and changed in a small range, the other forms had no obvious rule; The high percentage areas of effective form in total contents were also concentrated in the upstream and midstream regions, which was consistent with the analysis based on total contents.Through factor and cluster analysis, it could be found that most heavy metals was from multiple sources, the main pollution behavior was mining activities and urban pollution. The concrete classification and sources of six elements: A category for Cu, Cd, As, their main source was mining activities in Dexing ore district; A category for Pb, Zn, the main source was lead-zinc pollution near Jishui, then Dexing ore district in upstream and urban pollution in midstream, too; A category for Cr alone,it was mainly from mining activities in upstream region, then also a combined effect by urban industrial activities, sewage and transportation factors when it’s after Leping.Based on the pollution risk assessment of heavy metals’ total contents, it could be found that all elements after Gukou section basically were in severe pollution levels except Cr, of which the most polluted element was Cd, its regional average Geo-accumulation index value reached up to 4.34, located between severe pollution level and extreme pollution level, Cu, Pb, Zn followed; From the location, the mostpolluted section was Gukou, most elements’ highest concentrations had acquired in this section; The most polluted interval was between Gukou and Hushan, basically all pollution extremum areas of elements were gathered here, Leping area followed; The whole region of Le’an River was characterized by extreme pollution level; The study area could be divided into 6 ranges by comparison between Chernoff faces:(1) Clean area in source;(2) Severe pollution level area decreased with space in upstream;(3)Stable high pollution level area in middle and upper reaches;(4) Pollution transition area in midstream;(5) Pollution rise area in middle and lower reaches;(6) Low pollution level area decreased with space in downstream. Based on the pollution risk assessment of heavy metals’ forms, it could be found that pollution degree between sections fluctuated greatly, there was no clear rule in it, but severe pollution level area was significantly concentrated in middle and upper reaches, all elements showed severe pollution level in this interval; Pollution level of sections in downstream was relatively low, and there was no pollution at the source, elements Cu, Zn, Cd were characterized by heavy pollution, relatively light for Cr, As, all these were consistent with the assessment results based on total contents.