Optimization of Potential Ecological Risk Index Method for Soil Heavy Metals——A Case Study of Chengkou County, Chongqing City
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摘要:
目的 优化潜在生态风险指数评价标准,使其更适用于土壤重金属污染评价。 方法 参考瑞典学者Håkanson的方法,以城口县115件表层土壤中镉(Cd)、铬(Cr)、铜(Cu)、镍(Ni)、铅(Pb)和锌(Zn)等6种重金属为研究对象,基于重金属毒性系数,并结合内梅罗综合污染指数法(PN),以期验证潜在生态风险指数(RI)评价标准优化的适用性。 结果 ① 优化了土壤中6种重金属潜在生态风险评价分级体系:RI < 60,60 ≤ RI < 120,120 ≤ RI < 240,240 ≤ RI < 480,RI ≥ 480分别代表轻微、中等、强、很强、极强潜在生态风险。 ② 案例区6种重金属含量均值(算术均值,下同)分别为中国农用地土壤风险筛选值的5.0、0.39、0.52、0.44、0.23和0.76倍。③ 内梅罗污染评价显示,Cd处于重度污染[Pi(Cd) = 5.25],其余重金属处于无污染水平,PN显示土壤重金属整体处于重度污染(PN = 3.94)。④潜在生态风险评价结果显示,RI介于22.9 ~ 1582,均值196。优化前,案例区土壤6种重金属处于中等生态风险(优化前分级,150 ≤ RI < 300),而优化后处于强潜在生态风险。 结论 案例验证研究表明,优化后的潜在生态风险评价分级体系适合土壤重金属污染潜在生态风险评价,能客观反映土壤重金属污染状况。 Abstract:Objective The grading standards of potential ecological risk index is optimized to be more suitable to assess the potential ecological risk of soil heavy metal contamination. Methods According to Håkanson principle, six heavy metals (Cr, Cu, Cd, Ni, Pb and Zn) in the topsoil samples from Chengkou County were selected as research subjects. This study estimated and verified the suitability of optimized grading standards of potential ecological risk index (RI) of soil contamination, based on the toxic-response factor (Tri) and Nemerow pollution index (PN). Results ① The potential ecological risk levels of soils contaminated by the 6 heavy metals were suggested: RI < 60, 60 ≤ RI < 120, 120 ≤ RI < 240, 240 ≤ RI < 480 and 480 ≤ RI represent the low, moderate, considerable, high, and very high potential ecological risk, respectively. ② The mean values (arithmetic mean, similarly hereinafter) of the six heavy metals in the study area were 5.0, 0.39, 0.52, 0.44, 0.23, and 0.76 folds higher than the standard value for soil contamination of agricultural land, respectively. ③ The value of PN was 3.94, indicating that soil heavy metals contamination was severe pollution level (PN > 3) in the study area. The Cd contamination in soil was severe pollution level [Pi (Cd) = 5.25], while other soil heavy metals were no pollution. ④ Potential ecological risk assessment results showed that RI value ranged from 22.9 to 1582 with a mean of 196. Before optimization, soil heavy metals contamination (RI = 196) was the moderate potential ecological risk (pre-optimization classification, 150 ≤ RI < 300). After optimization, soil contamination, however, was the considerable potential ecological risk. Conclusions Case verification indicated the optimized grading standards of the potential ecological risk index could really show the potential ecological risk level of soil heavy metal contamination. -
Key words:
- Soil /
- Heavy metal /
- Potential ecological risk index
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表 1 Håkanson原文中潜在生态风险系数和指数评价标准[27]
Table 1. Grading standards of potential ecological risk in the original manuscript of Håkanson [27]
潜在生态风险系数Eri
Potential ecological
risk factor潜在生态风险指数RI
Potential ecological
risk index生态危害等级
Ecological hazard
level< 40 < 150 轻微 40 ~ 80 150 ~ 300 中等 80 ~ 160 300 ~ 600 强 160 ~ 320 ≥ 600 很强 ≥ 320 − 极强 表 2 优化后的潜在生态风险系数和指数评价标准
Table 2. Optimized grading standards of potential ecological risk
潜在生态风险系数与指数
Potential ecological risk factor and index元素
Element生态危害等级
Ecological hazard level轻微
Low中等
Moderate强
Considerable很强
High极强
Very highEri Cd < 30 30 ~ 60 60 ~ 120 120 ~ 240 ≥ 240 Cr < 2 2 ~ 4 4 ~ 8 8 ~ 16 ≥ 16 Cu < 5 5 ~ 10 10 ~ 20 20 ~ 40 ≥ 40 Ni < 5 5 ~ 10 10 ~ 20 20 ~ 40 ≥ 40 Pb < 5 5 ~ 10 10 ~ 20 20 ~ 40 ≥ 40 Zn < 1 1 ~ 2 2 ~ 4 4 ~ 8 ≥ 8 RI < 60 60 ~ 120 120 ~ 240 240 ~ 480 ≥ 480 表 3 土壤重金属含量统计特征
Table 3. Content statistical characteristics of heavy metals in soil
元素
Element最大值
Maximum
(mg kg–1)最小值
Minimum
(mg kg–1)算术均值
Arithmetic mean
(mg kg–1)标准差
Standard deviant变异系数
Coefficient of variation
(%)Cd 14.0 0.1 1.5 2.1 139.0 Cr 301.0 27.4 79.5 31.9 40.0 Cu 224.0 6.1 51.8 33.5 65.0 Ni 158.0 16.8 44.7 22.1 49.0 Pb 58.7 6.5 27.9 7.6 27.0 Zn 819.0 26.5 191.0 138.0 72.0 -
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