长江干流沿江地区土壤重金属的分布、来源及潜在生态风险

    Distribution, sources and potential ecological risks of soil heavy metals in the main stream of the Yangtze River

    • 摘要: 为掌握长江干流沿江地区土壤重金属状况,开展土壤表层样品采集和重金属空间分布研究,使用PMF(positive matrix factorization)模型解析土壤重金属来源,并选取地累积和潜在生态风险等方法,评估重金属的污染状况和生态风险。结果表明:1)土壤重金属的积累程度不同,As、Cd和Cu的超标率高,污染明显。Cd和Cu的变异系数高于1.0,分布不匀,受某些污染源的影响显著。2)各重金属含量呈现条带状的空间格局,在多个地区出现高值,土壤环境质量受到人类活动的负面影响。3)土壤重金属积累主要来源于自然、工业排放、交通运输和农业生产,贡献率分别为36.65%、28.48%、20.07%和14.80%。其中Cd与工业活动有关,Pb和Zn来自交通排放,Cr和Ni与自然源密切相关,As和Cu来源于农业生产。4)Cd的污染程度最高,81.88%的点位达到轻度污染。40%以上的点位受到As、Cu、Ni和Pb污染。75%以上点位的Cr和Zn含量较低,污染程度不高。单项生态风险指数的均值从大到小依次为:Cd、As、Ni、Cu、Pb、Zn、Cr。综合生态风险指数均值为63.17,处于轻微风险水平。该研究作为土壤生态调查的核心,可为土壤环境管理和重金属污染修复提供科学依据。

       

      Abstract: This study aims to explore the spatial distribution of soil heavy metals in the Main Stream of the Yangtze River. The contents of As, Cd, Cr, Cu, Pb, Ni and Zn were collected from the 741 topsoil samples. The positive matrix factorization (PMF) model was used to analyze the sources of heavy metals. The geoaccumulation index and potential ecological risk index were selected to assess the pollution and ecological risks of soil heavy metals. The results showed that: 1) The average contents of soil heavy metals As, Cd, Cr, Cu, Ni, Pb, and Zn were 13.50, 0.49, 79.96, 40.85, 34.33, 32.65, and 103.72 mg/kg, respectively. Except for Ni, the maximum content of the rest elements already exceeded the screening value, according to the national standard of soil environmental quality. But the average content of each element was within the screening value. Meanwhile, the accumulation of As, Cd, and Cu was found in the highest exceeding rate and severe pollution. The coefficient of variation of each element ranged from 0.34 to 2.20, where Cd and Cu shared the coefficient of variation higher than 1.0, indicating the uneven distribution and significant influence from local pollution sources. 2) The content of various heavy metals presented a strip-shaped spatial pattern with multiple high-value areas. The soil environmental quality was negatively affected by human activities. There were similar distribution patterns of As and Pb, Cd and Cr, as well as Cu and Zn. The spatial distribution of Cd differed significantly from As element. Specifically, the areas of high-value Cd were in Wuhan and Ezhou, Hubei Province, while the rest were in Anqing and Chizhou, Anhui Province. The content of soil heavy metals ranged from the middle and lower to the higher level in the study area, such as chemical, smelting, printing, and dyeing industries. 3) The natural, industrial emission, transportation, and agricultural production sources contributed the rates of 36.65%, 28.48%, 20.07%, and 14.80%, respectively. Among them, Cd was related to industrial activities, Pb and Zn were from transportation emissions, Cr and Ni were closely related to natural sources, as well as As and Cu were from agricultural production. Overall, 63.35% of soil heavy metals were from human activities. The important sources were chemical, steel, transportation, and agricultural production. 4) The highest degree of Cd pollution was 81.88% of points, indicating a level of mild pollution or above. Furthermore, more than 40% of the sites were contaminated with As, Cu, Ni, and Pb with a moderate level of pollution. More than 75% of the sites were not contaminated with Cr and Zn, where the soil condition was less affected by these two heavy metals. The average of the single ecological risk index was ranked in descending order as follows: Cd>As>Ni>Cu>Pb>Zn>Cr. The average comprehensive ecological risk index was 63.17 at a mild risk level, indicating the spatial distribution pattern. The soil investigation can provide the scientific basis for soil environmental management and heavy metal pollution remediation.

       

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