中文摘要：

采用改进后的BCR四步连续提取法,分析了甘肃省白银市黄灌农业区农田土壤5个土层重金属Cd, Cu, Pb, Zn的4种赋存形态,并依其污染指数和潜在生态危害指数,评价了白银黄灌农业区各层土壤中重金属的污染程度及其潜在生态危害.结果表明：白银黄灌农业区土壤重金属各形态质量分数（包括重金属总量）均在表层中达到最大值,而在中层最低.各层土壤中Cu以残渣态为主,占比为72.83%～91.80%.除表层外, Pb, Zn也以残渣态为主,占比分别为57.14%～70.19%,69.56%～80.95%,而Cd各形态在不同土层中没有呈现规律性分布.根据污染水平,各层土壤中4种重金属的污染程度顺序均为Cd〉Pb〉Zn〉Cu.根据潜在生态危害,各层土壤中4种重金属的潜在生态危害顺序均为Cd〉Pb〉Cu〉Zn,其中Cd的污染程度最高,潜在生态危害最强,表层尤其突出.综合本研究结果,白银市黄灌农业区土壤Cd污染严重,亟需整治以减小其对当地农作物及居民的潜在危害.

英文摘要：

The chemical speciations of heavy metals （Cd, Cu, Pb and Zn） in five layers of irrigated lands of the Yellow River in Baiyin were analyzed by means of the modified BCR-sequential extraction procedure. Elemental contamination index and integrate ecological risk index were employed to assess the contamination degree and potential ecological risks of heavy metals. The results showed that the mass fractions of heavy metals’ specia-tions in the surface layer of the studied area reached the highest level, while those in the middle layer hit the lowest point. Besides, Cu in different layers mainly existed in residual form, accounting for 72.83%～91.80%. Pb and Zn were also chiefly presented in residual form in different layers, except for the surface layer, representing 57.14%～70.19% and 69.56%～80.95% respectively. Moreover, speciations of Cd did not regularly distribute in different layers. According to elemental contamination index and integrate ecological risk index, the contamina-tion degree and the potential ecological risk of detected heavy metals was Cd〉Pb〉Zn〉Cu and Cd〉Pb〉Cu〉Zn respectively, of which Cd in the surface layer was the highest. In conclusion, Cd pollution in Baiyin farmland soil is rather severe. Therefore, it is suggested that strict measures must been taken to diminish the potential hazard of Cd to local crops and inhabitants.