State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China.
School of Environmental Science and Engineering, Guangzhou University, Guangzhou 510006, China.
Sci Total Environ. 2021 Mar 15;760:143426. doi: 10.1016/j.scitotenv.2020.143426. Epub 2020 Nov 1.
This study investigated the pollution, fractionation and potential risks of heavy metals in soils from a mountainous area with black shale outcropping, with emphasis on Cd and Zn. Elevated concentrations of heavy metals in black shales reflected high geochemical baseline in the study area. Metals released from oxidative weathering were redistributed and retained during pedogenic processes, leading to enrichment of Cd, Cu, Cr, Ni, V and Zn in soils. As a highly concerned metal pollutant, the content of Cd in all collected samples (N = 112, Cd: 0.44-16.1 mg/kg) exceeded the risk screening value for Chinese agricultural land. Metals in local soils were retained through adsorption onto soil constituents clay minerals and FeMn oxides and/or precipitation within secondary minerals. Based on sequential extraction, Cd and Zn fractionated in soils, with Cd mainly occurring in the mobile fraction (47.9% to 78.7%) as adsorbed, FeMn oxides and carbonate associated phases, whereas residual fraction (67.1%) dominated for Zn, followed by FeMn oxides coagulation (17.9%). Metals in residual soils from slopping location were highly related to metals in the parent rocks distributed more heterogeneously than metals in alluvial soils from flat location. High levels of heavy metal pollution in soils posed potential risks to the local eco-environmental systems and community, and Cd was highly concerned due to its high mobility. Cultivation in alluvial soils from valleys poses less risk than in residual soils, but appropriate approaches to reduce the risk in local soils is still necessary. The findings from this study provide basic knowledge and insight for risk control and targeted management of soils with geogenic heavy metal pollution in black shale outcropped mountainous areas.
本研究调查了一处富含黑色页岩露头的山区土壤中重金属的污染、分馏和潜在风险，重点关注 Cd 和 Zn。黑色页岩中重金属的高浓度反映了研究区域内高地球化学基线。在成土过程中，氧化风化释放的金属重新分布并被保留下来，导致 Cd、Cu、Cr、Ni、V 和 Zn 在土壤中富集。作为一种高度关注的金属污染物，所有采集样本（N=112，Cd：0.44-16.1mg/kg）中的 Cd 含量均超过了中国农用地的风险筛选值。通过土壤成分粘土矿物和 FeMn 氧化物吸附以及次生矿物内沉淀，土壤中的金属得以保留。基于连续提取，土壤中 Cd 和 Zn 分馏，Cd 主要以吸附态、FeMn 氧化物和碳酸盐结合相的可移动态（47.9%至 78.7%）为主，而 Zn 主要以残留态（67.1%）为主，其次是 FeMn 氧化物凝聚态（17.9%）。坡地残积土中的金属与分布更不均匀的母岩金属密切相关，而冲积土中的金属则不如冲积土中的金属密切相关。土壤中重金属污染程度高，对当地生态环境系统和社区构成潜在风险，由于 Cd 具有较高的迁移性，因此受到高度关注。与残积土相比，在河谷冲积土中种植的风险较小，但仍需要采取适当的方法来降低当地土壤的风险。本研究为控制和有针对性地管理黑色页岩露头山区具有地球化学成因的重金属污染土壤提供了基础知识和见解。
