Occurrence,adsorption and transport mechanism of microplastics in soil
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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