基于三角模糊数的清河沉积物重金属评价

Assessment of Heavy Metals in Sediments of Qinghe River Based on Triangular Fuzzy Numbers

为全面了解北京清河沉积物重金属的空间分布及污染水平,在清河采集8个沉积物样品,测定w(As)、w(Cd)、w(Cr)、w(Cu)、w(Pb)、w(Zn),并利用基于三角模糊数的地累积指数模糊评价模型对北京清河沉积物的重金属污染进行评价.结果表明:北京清河沉积物中w(As)、w(Cd)、w(Cr)、w(Cu)、w(Pb)、w(Zn)的平均值分别为43.18、1.20、70.70、49.62、38.59和297.36mg/kg,不同重金属在各采样点间的分布差异较大,6种重金属的污染程度表现为As>Cd>Zn>Cu>Pb>Cr.对于大部分采样点,基于三角模糊数的不确定性评价结果与常规评价结果保持一致,均显示清河沉积物重金属污染程度较低.然而,QH6采样点(立水桥)As常规评价结果为偏中度污染,不确定性评价结果为中度污染;QH5采样点(清河大桥)Cd和Zn在常规评价结果为轻度污染,而不确定性评价结果为偏中度污染;QH8采样点(入温榆河口)Cd和Zn常规评价结果分别为轻度污染和偏中度污染,不确定性评价的结果则显示为偏中度和中度污染.不确定性评价方法采用重金属质量分数区间值,而常规评价则采用重金属质量分数的单一值;不确定性评价通过计算隶属度确定污染等级,在接近分级界限时,不确定性评价和常规评价结果之间出现差异.

The concentrations of six heavy metals（ As,Cd,Cr,Cu,Pb and Zn） were analyzed in eight surface sediments sampled from Qinghe River,Beijing,to understand their spatial distribution. Based on the geo-accumulation indexes model modified with the triangular fuzzy numbers theories,the pollution of heavy metals in the surface sediments of Qinghe River were comprehensively evaluated. The results showed that the average concentrations of As,Cd,Cr,Cu,Pb and Zn were 43. 18,1. 20,70. 70,49. 62 and 297. 36 mg/kg,respectively,though the levels of heavy metals in different sample sites differed greatly. The aggregative pollution degree of measured heavy metals in the surface sediments were As Cd Zn Cu Pb Cr. Both the modified geo-accumulation index model and the ordinary evaluated model showed that the pollution degree of heavy metals in the sediments of Qinghe River was low. The modified geoaccumulation indexes model provided the same results of heavy pollution for most of the sediment samples as ordinary evaluation. The algorithm of uncertainty evaluation and ordinary evaluation are different; the former adopts interval values rather than a single concentration value. When the interval values were close to the grading limit,the uncertainty evaluation commonly gave more stringent assessment results than the ordinary evaluation. The sediment pollution of As at QH6 was assessed at a lower intermediate level by the ordinary evaluation,while intermediate level by the uncertainty evaluation. Similar results were found at site QH5 and QH8 for assessing the pollution of Cd and Zn.