包头-白云鄂博地区重金属基线值的厘定及其在重金属污染分级评价中的应用

论文运用地球化学基线原理,以参比元素标准化法和累积频率曲线法分别计算包头市区、白云鄂博矿区土壤As、Cr、Cu、Ni、Pb、Zn的基线值。结果显示,白云鄂博重金属基线值普遍高于包头。采用单因子指数法评价污染程度,以内蒙古背景值为标准时白云鄂博重金属轻微污染、轻度污染、中度污染样品比例分别为包头的1.0、1.5、1.7倍,白云鄂博重金属污染显著高于包头;以基线值为标准时包头和白云鄂博样品重金属均以无污染和轻微污染为主,且样品所占比例相当,表明两区污染程度没有显著差异。使用厘定的基线值进行重金属污染评价反映了包头和白云鄂博重金属污染的实际人为输入,而使用内蒙古土壤重金属背景值则无法反映两地重金属自然背景的差异,导致评价结果失真。

Determination of Heavy Metal Baseline in Baotou and Bayan Obo and Its Application in the Assessment of Heavy Metal Contamination

Based on the principle of geochemical baseline, the baseline values of six heavy metals, including As, Cr, Cu, Ni, Pb and Zn in Baotou city and Bayan Bbo mining area were determined with reference element method and cumulative frequency curve method. Baseline with reference element method was, at Baotou: 8.85 mg/kg As, 123.15 mg/kg Cr, 24.61 mg/kg Cu, 19.72 mg/kg Ni, 27.39 mg/kg Pb and 74.25 mg/kg Zn; at Bayan Obo: 16.16 mg/kg As, 127.17 mg/kg Cr, 31.07 mg/kg Cu, 28.94 mg/kg Ni, 33.82 mg/kg Pb and 80.52 mg/kg Zn. Baseline with cumulative frequency curve method was, at Baotou : 8.45 mg/kg As, 113.78 mg/kg Cr, 16.12 mg/kg Cu, 16.23 mg/kg Ni, 19.66 mg/kg Pb and 48.59 mg/kg Zn; Bayan Obo: 16.01 mg/kg As, 121.56 mg/kg Cr, 21.85 mg/kg Cu, 29.37 mg/kg Ni, 24.32 mg/kg Pb and 72.89 mg/kg Zn. Generally, the baseline values of Bayan Obo was higher than those in Baotou. The contamination of various heavy metals in Baotou and Bayan Obo were assessed using single-factor contamination index. When the background values of Inner Mongolia were used as the references, the numbers of none, slight, mild and moderate contaminated samples in Bayan Obo were 0.3, 1.0, 1.5 and 1.7 times of those in Baotou, indicating the contamination in Bayan Obo was higher than in Baotou. However, when baseline values were used as the references, the numbers of none, slight, mild and moderate contaminated samples in Bayan Obo were 1.0, 1.1, 0.7 and 0.5 times of those in Baotou. Since both areas had small numbers of moderately contaminated samples, no significant differences between Baotou and Bayan Obo was actually seen at contaminative levels. Assessment of the contamination of heavy metals in these two areas using the baselines reflected reasonable contributions of human activities, whereas using background values of Inner Mongolia gave rise to distorted recognition of such contributions.