【摘要】 农田土壤作为保证粮食安全及人类发展的重要资源,近年来其受到的重金属污染备受关注。文章选取长三角发达地区某田块作为研究对象来分析同源情形下重金属的污染特征及主要影响因素。结果表明:该田块Cd平均质量分数为3.74 mg/kg,超出二级标准值达12.5倍,高值区主要分布在入水口及出水口附近。其余重金属元素(Pb,Cr,As,Co,Cu,Ni,Zn)均未超标。运用地累积指数、Hakanson潜在风险指数、内梅罗综合污染指数等多种污染评价方法均发现,Cd的严重超标导致该田块已达到重金属污染的最高等级。采用相关分析及通径分析方法,揭示了Cd污染的主要影响因素,Cd与土壤理化性质在0.01水平上均不存在显著相关,表明与持续的Cd外源输入相比,土壤对Cd的吸附能力极其有限。距入水口出水口的距离是影响Cd空间差异的最直接因素和决定性因素。减少外源Cd的持续输入及改良灌溉排水设施是解决田块Cd重污染的有效途径。更多还原

【Abstract】 As one of the most important resources about assuring food security and human development, the agricultural soil and its pollution has been widely reported these years. A certain field in Yangtze River Delta was selected as our study area to analyze the agricultural soil heavy metal pollution characteristics and its main influence factors in case of the same pollution sources. We collected 30 soil samples to analyze their heavy metal concentration(Cd, Pb, Cr, As, Co, Cu, Ni and Zn) and soil physico-chemical properties(i.e. EC, CEC, p H, OC, clay content). The results showed that the average Cd concentration in this field was 3.74 mg/kg soil, which exceeded the China Tier II environmental standard value by 12.5 times. The highest value of Cd even exceeded the Tier II environmental standard value by 44.7 times. The Cd was mainly accumulated at the top soil. The mean concentrations of Cd at the top and down soil were 4.44 mg/kg soil and 2.09 mg/kg soil, respectively. The high values of Cd were mainly distributed at the area nearby the water inlet and outlet. The Pb of soil samples that exceeded the soil background value accounted for 90%, but the Pb concentrations of all soil samples did not exceed the China Environmental Quality Standard(Tier II). The mean Pb concentration of top and lower soil were 33.98, 26.29 mg/kg soil. All soil samples of Cr, As, Co, Cu, Ni and Zn had no pollution. The CV of Cd at the top soil was 64%, which was extremely higher than that of other heavy metals(about 6% of Zn, and about 15% of As). Ni, Cu, Zn had small spatial variation, which indicated that the filed had similar sources. Three pollution evaluation method: geo-accumulation index(Igeo), Hakanson potential ecological index(EI), and Nemerow pollution index(NPI) were used to evaluate the heavy metal pollution level. We found that most of the soil samplers had high Cd Igeo(mean: 5.82), which were identified as "severe contamination". The mean EI of soil samples were 2 566.97, which exceeded 4.3 times of the lowest value of "highest ecological risk". Moreover, the NPI ranged from 2.99-217.02(mean value: 60.58). All these evaluation showed that the extremely serious soil Cd pollution caused the highest pollution level in this field. Moreover, we used the correlation analysis and path analysis to identify the main influence factors of Cd pollution in a situation of similar sources at a filed scale. The Cd did not significantly correlate with every index of soil physicochemical properties. It can be indicated that the Cd through soil adsorption were extremely lower than the Cd through external source import. The distance from the water inlet and outlet was the most direct and determinant factor at the field scale. The north of this field was drainage outlet. The Cd can flow into the field with water through water inlet. So Cd concentration of the northern field decreased with the distance of water inlet. And water flow velocity slowed down when the water in the field reached the surrounding of water outlet, which caused accumulation of Cd nearby the outlet. Decreasing the Cd of persistent external source import and improving the irrigation and drainage facilities were the efficient way to reduce the severe Cd pollution.更多还原