| With the rapid development of modern agriculture and industry as well as the accelerating process of urbanization, the pollution caused by heavy metals in soil is becoming more and more serious. The heavy metal pollution of farmland and food safety issuesis closely related to human health, which has been highly concerned by people. Hu County, in Shaanxi Province, is an important agricultural production base of Guanzhong region, which supply grain, fruit, vegetables and other agricultural products to around large cities. Therefore, study on the heavy metals enrichment and pollution in soil of this region has more important theoretical and practical significance. This study selected the grapery, kiwi fruit orchard, wheat field, vegetable field in Qing town and the grapery, vegetable field around Yuxia Coal-Fired Power Plants (CFPP) as sample polts, meanwhile collected all kinds of soil samples. The concentration of heavy metal elements (e.g. As, Co, Cr, Cu, Mn, Ni, Pb, Zn) and constant elements (e.g. Fe, Ca, K, Mg, Na, Si, Al) in soil digested by the X-Ray Fluorescence Spectrometry. The physiochemical properties of soil, such as pH values, electrical conductivity (EC), magnetic susceptibility and soil granularity, were analyzed by using pH Meter, Conductivity Meter, Magnetic Susceptibility Meter and Laser Particle Size Analyzer. The distribution and enrichment characteristics of eight heavy metal elements in soil profile were studied, and the heavy metal pollution of different types of agricultural land was also evaluated and corresponding remediation measures were put forward. At the same time, the method of multivariate statistical analysis was used to study the sources of heavy metal elements in the soil of agricultural land at Hu County. The main conclusions of this paper are as follows:(1) The average value of pH in soil of agricultural land at Hu County is 7.89, belong to the partial alkaline soil. The average value of electrical conductivity is 200.61 ?S/cm, the maximum value is 375.00 ?S/cm and the minimum value is109.00 ?S/cm. The range of the low frequency magnetic susceptibility of the soil is 12.40×10-8 m3/kg?201.00×10-8 m3/kg, and the average value is111.51×10-8 m3/kg; the range of the high frequency magnetic susceptibility is 12.10×10-8 m3/kg?200.50×10-8 m3/kg, and the average value is 111.09×10-8 m3/kg; the average value of frequency magnetic susceptibility is 0.57%. The particle size distribution of soil is characterized by generally the content of coarse silt is most, followed by clay, medium sand and coarse sand with the least content, and no gravel appears.(2) The heavy metal elements in the study area has a layered enrichment features. There is a phenomenon that is some heavy metal elements enriched in the soil surface, more special is that there are kinds of heavy metal elements enriched obviously in the lower of soil profile, and some heavy metal elements both in soil surface and profile bottom also have certain enrichment.(3) There are significant differences in enrichment depth between the different kinds of heavy metal elements which in different types of agricultural land. The enrichment depth of eight kinds of heavy metal elements in vegetable field is deepest, mainly enriched in the lower of the soil profile. In contrast, the enrichment of them in other sample plots with a shallower depth. Among them, As, Co, Cr, Cu, Pb, Zn mainly enriched in the depth above 0.5 m, and Mn as well as Ni mainly enriched in 0?1.0 m depth range of soil profile.(4) The assessment results of Enrichment Factor and Geoaccumulation Index showed that Cr in each layer of the soil profile at the six sample plots was slightly polluted. Mn up to a slight pollution level in 0.6?1.0 m depth range of soil profile, and reach to middle pollution level in 1.1?1.2 m depth range of soil profile at the grapery around Yuxia CFPP. Cu and Zn in soil profiles of all sample plots are in a practically unpolluted level. In addition, As, Co, Ni and Pb have different degrees of pollution in different types of agricultural land.(5) The results of Nemerow Pollution Index (Pn) indicated that the value of Pn of agricultural land in Qing town showed kiwi fruit orchard>wheat field>vegetable field>grapery. In detail, the soil of kiwi fruit orchard was moderately polluted in 0.1?0.2 m,0.45?0.6 m,0.9?1.0 m,1.9?2.0 m depth range, and was polluted slightly at other depth. The soil of wheat field was moderately polluted in 0-0.35 m and 0.6?1.1 m depth range, and was polluted slightly in 1.1?2.0 m depth range. While, the soil of vegetable field and grapery both in unpolluted level. The results also indicated that the value of Pn of agricultural land around Yuxia CFPP showed grapery>vegetable field. In detail, the soil of grapery was moderately polluted in 0-0.8 m depth range, and was heavily polluted in 0.8-1.2 m depth range. While, the soil of vegetable field was moderately polluted in whole profile. The results of Potential Ecological Risk Index (RI) indicated that the value of RI of agricultural land in Qing town showed wheat field>kiwi fruit orchard>grapery>vegetable field, while the value of RI of agricultural land around Yuxia CFPP showed grapery>vegetable field, and all the six sample plots were at a low risk level.(6) The comparison results, which about distribution and pollution of heavy metals in soil between agricultural land around Yuxia CFPP and Qing town, showed that the soil pollution caused by heavy metals in agricultural land around Yuxia CFPP was more serious than Qing town. It can be seen that the soil around Yuxia CFPP suffered more seriously polluted by heavy metals.(7) Eight kinds of heavy metal elements in soil of agricultural land at Hu County can be divided into three categories. The first part is the Co and Cr, mainly comes from human activities, including atmospheric deposition, agricultural pollution and traffic pollution. The second part is Cu, Pb and Zn, which main sources include natural and human pathways. The third part is As, Mn and Ni, which main source affected by both natural factors and human factors. |
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