长江三角洲典型城市农田土壤重金属累积特征与来源

研究农田土壤重金属累积特征和来源对科学管理、安全利用土壤资源具有重要意义。通过野外采样与实验室分析研究了长江三角洲典型城市农田土壤重金属(Cd、Hg、As、Pb、Cr、Cu)含量、累积状况,识别了农田土壤重金属来源。结果表明:(1)六种土壤重金属的累积程度按照由重到轻的顺序为:Hg>Cd>Cu>As>Pb>Cr;(2)以《土壤环境质量-农用地土壤污染风险管控标准》(GB 15618-2018)为参考,土壤中Cu、Cd和Hg超过风险筛选值的比例分别为2.13%、1.06%和0.53%,As、Pb和Cr未超过风险筛选值;利用地累积指数法进行土壤重金属污染评价发现,Cd和Hg的污染较其他四种元素严重,其污染比例分别为12.83%和21.28%;(3)地理探测器分析表明,化肥和农药的使用量以及工业总产值均能解释六种重金属的空间分异,其他环境因子能解释某些特定重金属的空间分异;(4)研究区土壤中As和Cr的主要来源为农业源和工业源;Cd和Hg的来源除了农业源与工业源外,还有土壤母质;Cu来源与研究区农业活动、畜禽养殖活动以及工业活动有关,Pb主要来源于农业源、工业源和交通源。总之,研究的六种重金属存在不同的累积趋势,农业和工业活动是研究区土壤重金属累积的主要原因。研究区交通、社会活动等对土壤重金属累积的影响还需进一步研究与讨论。

Accumulation and Sources of Heavy Metals in Agricultural Soil in A City Typical of the Yangtze River Delta, China

Objective] Zhangjiagang City, located at the Yangtze River Delta, China, has experienced rapid economic development since the unfolding of the reform and opening up policy, and consequently the economic development has brought about a series of environmental problems that have aroused concerns among the society in recent years. For the purpose of scientifically managing soil resources and providing to decision-making support in the effort to control the heavy metal pollution problems from the source and to remedy contaminated farmland soils, this study was carried out to explore how heavy metals accumulate and to identify sources of the heavy metal pollutions in this city.Method] Totally, a total of 188 sampling sites were set up for collection of samples of surface and subsurface soils in the study area, in the light of soil types, land uses, sampling homogeneity, and surrounding contamination conditions. Totals of the six elements, i.e. Cd, Hg, As, Pb. Cr, and Cu, soil pH, and soil organic matter in the samples were measured. Sources and driving factors of the heavy metal pollution in the soil were analyzed and identified with the aid of principal component analysis (PCA) and GeoDetector.Results] Results show that:(1) In terms of accumulation degree, the six heavy metals follow a descending order:Hg > Cd > Cu > As > Pb > Cr; (2) With reference to the "Soil Environmental Quality Risk Control Standard for Soil Contamination of Agricultural Land (GB 15618-2018)", about 2.13%, 1.06% and 0.53%, respectively, of the farmland soils polluted with Cu, Cd and Hg had the elements exceed the criteria, while almost none of the farmland soils polluted with As, Pb, and Cr do. Pollution assessment with the Geo-accumulation index method shows that among the six heavy metals pollutants, Cd and Hg were the two major ones and detected in 12.83% and 21.28% of the sampling sites, respectively; (3) Performance of the GeoDetector shows that among all the nine factors (pH, soil organic matter, soil type, fertilization application rate, pesticide application rate, population density, GDP, distance from road, and industrial output) discussed in this study, fertilization and pesticide application rates as well as industrial output were the main factors contributing to spatial variation of the six pollutants, while population density, GDP and distance from road were the ones explaining spatial variation of Pb; and (4) As and Cr came mainly from agricultural and industrial activities, Cd and Hg came from soil parent materials in addition to agricultural and industrial activities, Cu in the surface soil came from agriculture, livestock breeding, and industrial activities, while Pb came mainly from agricultural, transportation and industrial activities.Conclusion] In summary, the six heavy metals in the study area vary in accumulation characteristics. Agricultural and industrial activities are the major causes leading heavy metals pollution of the soil. Nevertheless, further researches should be carried out to figure out influences of social and transportation activities on accumulation of some certain heavy metals, such as Pb.