Quality Evaluation Of Heavy Metals In Soil And Sediments From Yuelu District Of Changsha City

In the process of urbanization, a large number of heavy metal pollutants are taken into the environment. Heavy metals in the soil are difficult to degrade and easily accumulate. When accumulate over a certain content, heavy metals will put toxic effects on organisms and humans. In order to understand condition of heavy metal pollution in Yuelu District, Changsha City, the surface soil (0-20cm) and sediments in Xiangjiang (Changsha section) were sampled, tested and evaluated. The main research contents are as follows:1. This article summarized the sources of heavy metals, research status, detection technique and evaluation methods.2. Six kinds of heavy metals such as Cd, Cr, Cu, Ni, Pb and Zn were analyzed by ICP-AES. The ratios of recovery experiments were between79.5%-108.3, thus the research data can meet the requirements of heavy metal pollution assessment. Besides, the mathematical principles of Nemerow index, BP artificial neural network, Factor analysis method and Geostatistics method were explained in detail.3. The Yuelu district of Changsha city was divided into four zones as residential areas, traffic areas, old industry and new industry. In each zone, soil samples were randomly collected. Total31soil samples were digested by mixed solution of HCl-HNO3-HF-HClO4. The total heavy metals were determined by ICP-AES. Results showed:①soil in Yuelu district was characterized polluted by Cd and Zn. Especially, the average enrichment coefficients of Cd is up to3.22.②Considering Environment quality standard for soils, the Nemerow pollution index of old industry, new industry, traffic areas and residential areas was2.9,2.0,2.0and1.3and belong to close to heavy pollution, moderate pollution, moderate pollution and mild pollution respectively.③Considering the background of Yuelu soil and the flaw of Nemerow index method, this article constructed BP neural network evaluation model of Yuelu District soil. In all samples,54.8%samples belongs to the slight pollution level,38.7%samples belongs to the moderate pollution level. Specifically:soil environmental quality of residential area is the best, most belong to light pollution; traffic area is between mild and moderate pollution; new industrial district belongs to the moderate pollution; the old industrial area is between moderate and severe pollution. The BP evaluation model and the Nemerow index showed that surface soil of Yuelu District of Changsha City was between mild and moderate pollution.4. The data of As is quoted from The National Undergraduate modeling contest. this article use Matlab2010a program to analyze heavy metal spatial distribution based on geostatistics principle, including:the calculation and fitting of the variogram, selecting variogram model, the ordinary kriging interpolation of two-dimensional space and visualization of the interpolation results.5. To trace the sources of the heavy metals in sediments of Xiangjiang (Changsha section),10samples were collected systematically and dissolved using HCl-HNO3-HF-HClO4. The following elements were determined by ICP-AES:Al, Cd, Co, Cr, Cu, Fe, Li, Mg, Mn, Ni, Pb, Sr, V and Zn. Factor analysis and cluster analysis suggested that the heavy metals studied in Sediments of Xiangjiang (Changsha section) can be classified into three sources:Cu, Ni, Pb is from natural source; Cd and Zn pollution is controlled by the non-ferrous metal smelting; Cr pollution comes mainly from industrial activities in Sanchaji region.6. Ecological risk assessment of sediments in Xiangjiang (Changsha section) showed:①Igeo index indicated that Cd in sediment polluted most seriously,4/10samples ranked strong to strong pollution level, six reached strong pollution level. The followed was Zn, which belonged to strong pollution level. The orders of heavy metal in the sediments were: Cd>Zn>Pb>Cu>Cr.②The potential ecological risk evaluation indicated that the potential ecological index of Cd in sediment is the max and the mean value came to586.8, belonged o the strong ecological risk level. According to the composite index(RI), there were none points (RI <150),3points (150<RI<300),1point(300<RI<600),5points (600<RI<1200),1point (RI>1200). The mean value of RI reached604.5implying that Heavy metals in the surface sediments of the Xiangjiang River (Changsha section) polluted seriouslyand belonged to very high ecological risks.