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我国城市化进程的加快和人民生活水平的不断提高导致城市生活垃圾产生量急剧增加,据统计,我国城市生活垃圾年处理量从2017年(2.15亿吨)到2020年(预计2.82亿吨)的年增率为10%,垃圾的处理问题已成为了我国重要的环境问题之一[1]。目前我国处理城市生活垃圾的方式主要为填埋(65.5%)和焚烧(32.5%)[2]。而建立生活垃圾综合处理园区,完善焚烧、填埋等多种生活垃圾处理设施,综合调控生活垃圾流在各垃圾处理链中的循环流动,对于提高处理能力、实现可持续发展具有重要意义。长期的垃圾焚烧、填埋过程会不断以各种方式向周边环境释放重金属类污染物(如Cr、Cu、Ni、Zn、Pb、Hg等),与有机物不同,重金属不能被微生物降解,容易在土壤中不断累积和被植物摄入,重金属浓度过高时会对植物产生毒害作用,从而影响植物的生长[3],甚至能经食物链进入人体,对人类健康构成威胁[4]。已有研究证实垃圾处理园区会向周边土壤输送重金属[5],泰国、老挝及尼日利亚等国的垃圾处理场周边土壤和农作物中重金属均出现了积累,其中泰国垃圾填埋场的重金属赋存深度达2 m,且周边500 m内的土壤、水体和植被均被污染[6-8]。
生活垃圾综合处理园区向周边土壤输入重金属的路径有多种。在风力作用下,废旧电池、电器等重金属含量较高的垃圾焚烧所释放重金属(如Cr、Cu、Ni、Zn、Pb、Hg等)通过烟囱及无组织逸散等方式排放入大气中,随后沉降到土壤中[9];在雨水、河流侧向力等外力作用下,重金属元素随地表径流向下游土壤迁移;垃圾渗滤液携带着重金属元素经过土壤空隙向下层渗透[10],垂向迁移进入地下水后,沿地下水向下游迁移,而后经毛细水上升进入深层土壤[11]。这些污染途径叠加会产生不同的剖面分布特征,仅仅从表层取样是无法判别的。然而,现有研究大多关注于表层(0—20 cm)土壤中的重金属分布[12-14],针对不同深度土层中重金属分布特征及风险的研究尚少,既无法为判识重金属的输入来源提供依据,也无法实现对深层土壤和地下水的风险评估。因此,对生活垃圾处理设施周边,尤其是污染传输途径复杂的综合处理园区周边土壤剖面进行重金属分布特征和风险评估研究具有十分重要的意义。
本研究以某生活垃圾综合处理园区为研究对象,该园区包含生活垃圾焚烧厂和生活垃圾卫生填埋场。本研究的目的为:解析生活垃圾处理园区周边土壤中重金属Cr、Cu、Ni、Pb、Zn、As、Cd和Hg的空间分布特征;识别周边土壤中重金属主要输入及迁移路径,分析不同重金属可能的来源;评估垃圾处理园区周边土壤中重金属的污染程度及生态风险。
某生活垃圾处理园区周边土壤重金属分布特征及风险评价
Distribution characteristics and risk assessment of heavy metals in soil around an integrated waste management facility
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摘要: 为了评估青岛市某垃圾处理园区附近土壤重金属的分布特征及污染风险,采集了垃圾处理园区附近的剖面土壤样品,分析了土壤中重金属元素Cr、Cu、Ni、Pb、Zn、As、Cd和Hg的含量。结果表明,垃圾处理园区附近的0—200 cm深度的土壤中Cr、Cu、Ni、Zn、As重金属含量高于该区域相应的背景值,存在相应的重金属富集现象。由于垃圾处理园区存在向该区域土壤中输入重金属的多种叠加路径,重金属含量在不同点位的土壤剖面上呈现差异性的垂向分布特征。相关性和主成分分析结果表明,土壤中Cr、Cu、Ni、Pb、Zn和As的富集受人类活动影响,而Cd和Hg的来源主要受制于自然因素。各重金属的潜在污染指数大小排序为:Hg>Cd>As>Ni>Cu>Pb>Cr>Zn,综合生态风险指数(RI)均小于150,属于低风险。本研究为判定垃圾处理园区对周边土壤的影响路径以及辅助进行后续的管理提供了依据。Abstract: To assess the pollution characteristics and potential risks of heavy metal in the soil around an integrated waste management facility in Qingdao, profile soil samples were collected near the integrated waste management facility and concentrations of Cr, Cu, Ni, Pb, Zn, As, Cd and Hg were determined. The results revealed that the concentrations of heavy metals (Cr, Cu, Ni, Zn and As) in the soil with a depth of 0—200 cm near the integrated waste management facility were higher than the corresponding background values. Differences in the vertical distribution characteristics of heavy metals among the five soil profile sampling sites were observed, which might be attributed to the various transport paths of heavy metals from the integrated waste management facility to the surrounding soil. Pearson correlation coefficient and principal component analysis indicated that the abundance of Cr, Cu, Ni, Pb, Zn and As in soil were influenced by human activities, while Cd and Hg were mainly controlled by natural conditions. The potential pollution indices of heavy metals were in the order of: Hg>Cd>As>Ni>Cu>Pb>Cr>Zn, and the ecological risk index (RI) was less than 150, suggesting a low-level eco-risk potential. This study showed that the accumulation of heavy metals in this research site did not reach high pollution level, and therefore posed a low eco-risk potential in the profile soil near the integrated waste management facility. This study provides evidence for estimating the impact paths of the integrated waste management facility on the surrounding soil and assisting in subsequent management steps.
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表 1 垃圾处理园区周边区域土壤剖面中重金属含量(mg·kg−1)
Table 1. The total contents of heavy metals in the soil profiles near the integrated waste management facility(mg·kg−1)
采样点 Sampling sites Cr Cu Ni Pb Zn As Cd Hg TRZ-1 最大值Maximum 88.38 33.60 41.72 27.30 84.15 10.36 0.10 0.07 最小值Minimum 58.98 16.69 23.09 20.14 46.14 6.39 0.05 0.02 均值Average 69.94 23.49 30.56 23.23 60.13 8.15 0.07 0.03 标准差Standard deviation 10.91 5.71 6.76 2.26 13.38 1.47 0.01 0.01 变异系数Coefficient of variation/% 15.60 24.30 22.12 9.74 22.25 17.99 17.75 41.14 TRZ-2 最大值Maximum 82.90 29.90 38.72 26.07 75.10 9.75 0.11 0.04 最小值Minimum 59.77 18.87 24.20 20.23 49.95 6.64 0.04 0.03 均值Average 70.86 24.09 30.38 23.36 61.81 8.43 0.07 0.03 标准差Standard deviation 8.02 3.52 4.96 1.87 8.93 1.06 0.02 0.00 变异系数Coefficient of variation/% 11.31 14.62 16.33 8.00 14.45 12.51 29.64 12.06 TRZ-3 最大值Maximum 83.30 29.35 37.98 25.68 73.77 10.17 0.11 0.04 最小值Minimum 55.27 15.99 21.13 22.12 44.21 6.28 0.06 0.02 均值Average 69.67 22.51 29.82 24.04 59.73 8.19 0.08 0.03 标准差Standard deviation 7.91 3.70 4.75 1.32 8.34 1.08 0.02 0.00 变异系数Coefficient of variation/% 11.36 16.43 15.94 5.47 13.97 13.23 18.61 15.31 TRZ-4 最大值Maximum 86.60 32.47 40.85 27.79 80.94 11.73 0.10 0.04 最小值Minimum 74.13 26.26 34.65 24.74 68.65 8.30 0.05 0.02 均值Average 80.15 28.24 37.08 25.94 74.23 10.00 0.08 0.03 标准差Standard deviation 3.52 1.69 1.85 0.90 3.80 1.03 0.02 0.00 变异系数Coefficient of variation/% 4.39 5.99 4.98 3.46 5.12 10.33 20.60 14.53 TRZ-5 最大值Maximum 123.76 31.08 53.79 28.52 85.94 10.76 0.12 0.04 最小值Minimum 63.78 19.71 23.07 22.35 50.56 6.71 0.04 0.03 均值Average 82.44 27.02 36.55 25.82 71.31 9.26 0.09 0.03 标准差Standard deviation 15.49 4.08 8.27 2.25 10.77 1.46 0.02 0.01 变异系数Coefficient of variation/% 18.79 15.09 22.62 8.73 15.11 15.78 22.67 20.26 青岛市背景值Qingdao background value 47.48 18.50 18.63 29.63 56.68 5.76 0.14 0.04 GB 15618-2018 200.00 100.00 100.00 120.00 250.00 30.00 0.30. 2.40 上海老港垃圾填埋场Shanghai Laogang Landfill 89.50 33.20 − 100.20 12.60 − 0.20 − 老挝万象垃圾填埋场Laos Vientiane Landfill 10.02 11.70 5.65 4.39 16.03 − 1.02 − 广东龙港电子垃圾堆放场 Guangdong Longgang Electronic Waste Landfill 58.43 63.65 34.26 84.32 180.24 6.85 0.56 0.88 表 2 垃圾处理园区周边区域土壤中重金属之间的相关性
Table 2. Correlation between heavy metals in soil near the integrated waste management facility
元素Elements Cr Cu Ni Pb Zn As Cd Hg Cr 1 Cu 0.85** 1 Ni 0.97** 0.93** 1 Pb 0.72** 0.84** 0.80** 1 Zn 0.82** 0.95** 0.90** 0.91** 1 As 0.60* 0.79** 0.72** 0.85** 0.83** 1 Cd 0.04 −0.03 0.06 0.03 −0.05 0.14 1 Hg 0.13 0.12 0.12 0.04 0.08 0.11 0.08 1 注:** P<0.01;* P<0.05. 表 3 垃圾处理园区周边区域土壤中重金属的主成分表
Table 3. Principal component table of heavy metals in soil near the integrated waste management facility
主成分
Principal component特征值
Eigen values主成分载荷
Load of principal component特征值
Eigen values贡献率/%
Contribution rate累计贡献率/%
Cumulative contribution
rateCr Cu Ni Pb Zn As Cd Hg F1 5.18 64.78 64.78 0.89 0.97 0.96 0.92 0.98 0.85 −0.02 0.09 F2 1.09 13.60 78.38 0.07 0.01 0.08 0.01 −0.03 0.16 0.80 0.66 -
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