Pollution Characteristic And Assessment Of Heavy Metals In Water Of Si River

The research of this essay is focused on Si river, to analyzed the concentration andphysicochemical properties of heavy metals in7water samples from both trunk stream andtributaries, for studying the distribution characteristics of heavy metal in water and suspendedsolids, then the water quality was assessed using the fuzzy comprehensive assessment. Theresults indicated that the average concentration of different heavy metals in the water from SiRiver was in order of: Mn＞Zn＞Ni＞Cu＞Cr＞As＞Pb＞Cd＞Hg. Mn, Zn and Pb weremainly adsorbed by suspended solids, while Ni、Cu and As were mainly in water in the formof dissolved, which had relatively stronger ability to migrate. Hg、Cu、Zn and TN wereassessed using the fuzzy comprehensive assessment. The results showed that all the watersamples analyzed were reached or exceeded the surface water Class Ⅴ water standard. Hgand TN were the primary pollution elements.Heavy metals were persistent pollutants, which were seen as the important indicators ofwater environment pollution because of strong accumulation and toxicity of sediments. Theinfluence of human activities were able to be assessed through the study of sediments. Inorder to investigate the heavy metals concentration and their potential ecological risk of thesediments in Si River, the Index of Geoaccumulation and the Potential Ecological Risk Indexwere employed to evaluate the pollution degree of heavy metals in the surface sediments. Theresults indicated that the average concentration of Hg, Cd and Mn was above theenvironmental background values which showed a significant cumulative effect. Hg and Cdwere the predominant pollution elements. The descending order of pollution degree of variousheavy metals was: Hg＞Cd＞Mn＞Zn＞Ni≈Pb≈Cu＞Cr＞As; the potential ecological riskintensity caused by different heavy metal was: Hg＞Cd＞As＞Pb≈Cu＞Cr≈Zn.The pollution of water body sediment could be reflected by total amount of heavymetals, but it could not reflect the potential environmental risk to the environment effectively.The toxicity of heavy metals in water environment were mainly related to its speciation. Theactivities and rules of migration and transfer of heavy metals could be understood deeply bythe study of its speciation. Using an improved Tessier sequential extraction method to analyze the concentration of different speciation of Hg, As, Cd, Pb, Cr, Ni, Cu, Zn and Mn in7surface sediments from both trunk stream and tributaries in Si river, this article elaborated thedistribution characteristics of different heavy metals speciation, the Contamination factor(Cfi)and Risk assessment code(RAC) were used to quantificationally assess the ecological risk ofheavy metals. The result indicated that Cr and Ni mainly existed as residue fraction, Inaddition to residue fraction, the Cd, Mn and Cu of extractable form was higher, Pb wasmainly associated with Fe\Mn oxide fraction, Hg mainly existed in humic acid fraction, whilethe higher Fe\Mn oxide and humic acid fraction of As and Zn were observed. The relativeretention time of each heavy metal in the sediments from Si river was in the following order:Cd＞Mn＞Hg＞Cu＞As＞Pb＞Zn＞Ni＞Cr. Cd, Mn and Hg had relatively higher capacityof heavy metals to be released from the sediments. The RAC of different heavy metal was inorder of Cd＞Mn＞Cu＞Zn＞Pb＞Hg＞As＞Ni＞Cr, Cd and Mn showed high risk forenvironment, Cu showed medium risk for environment, Hg, As, Pb, Cr, Ni and Zn showedlow risk for environment in most samples.