摘要
塑料污染已成为备受关注的全球环境问题,土壤是塑料的主要汇集地之一,进入到土壤中的塑料会经过物理、化学和生物老化过程降解为微塑料.由于微塑料具有粒径小、难降解等特点,容易吸附土壤环境中共存的污染物,如有机污染物和重金属等,进而发生共迁移.本文总结了微塑料在全球不同地区土壤中的赋存特征,并探讨了土壤中微塑料的可能来源(农业地膜、工业活动、污水污泥等);归纳了土壤中微塑料对共存有机污染物和重金属的吸附机制以及影响因素(微塑料的理化性质和环境条件),微塑料吸附有机污染物和重金属的机制均包括孔隙填充作用、范德华力、静电力和阳离子-π键.除此之外,微塑料吸附有机污染物的机制还包括疏水作用、分配作用、氢键、π-π键、卤素键、负电荷辅助氢键和CH/π键;而络合(螯合)作用和离子交换在微塑料吸附重金属过程中起到了重要作用.综述了微塑料在土壤中的迁移机制(物理截留、静电力、疏水作用、氢键和络合作用等)以及影响因素;并进一步讨论了微塑料吸附和迁移行为对土壤理化性质及其生态毒性的影响.最后,对土壤中微塑料环境行为研究进行了展望.本文对于客观评价微塑料在土壤中的归趋和生态风险具有重要意义.
Abstract
Plastic pollution has become a global environmental problem of great concern.Soil is one of the main sinks of plastics,in which plastics can be broken into microplastics(MPs)by physical,chemical and biological degradation.Because MPs have the characteristics of small particle size and difficult degradation,they can exist in the soil for a long time,and it is easy to adsorb the coexisting pollutants(heavy metals and organic pollutants,etc.)in the soil environment,and then co-transport.This study provided a comprehensive review of the methods for detecting MPs in soil and the occurrence characteristics of MPs in soil in various regions around the world.Agricultural plastic film,industrial activities and sewage sludge may all be important sources of MPs in soil.In addition,the adsorption mechanism of MPs on coexisting organic pollutants and heavy metals in soil as well as its influencing factors was comprehensively summarized.Organic pollutants and heavy metals could be effectively adsorbed by MPs through pore filling,van der Waals interaction,electrostatic interaction and cation-π bonds.Moreover,the mechanisms of MPs adsorbing organic pollutants also involved hydrophobic interaction,distribution interaction,hydrogen bond,π-π interaction,halogen bond,negatively charged hydrogen bond and CH/π interaction,while complexation(chelation)and ion exchange played an important role in the adsorption of heavy metals by MPs.The properties of MPs and environmental conditions all affected the adsorption of organic pollutants and heavy metals by MPs.The transport mechanism of MPs in soil and its influencing factors were well reviewed.The physical and chemical properties of MPs,soil properties and environmental factors affected the transport of microplastics in soil.The effects of adsorption and transport behavior of MPs on soil physical and chemical properties and ecological toxicity were further discussed.Finally,the researches on the environmental behavior of microplastics in soil were envisioned.This paper is of great significance for objectively evaluating the fate and ecological risk of microplastics in soil.
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