微塑料的老化特性、机制及其对污染物吸附影响的研究进展

A review on aging characteristics,mechanism of microplastics and their effects on the adsorption behaviors of pollutants

针对微塑料的老化特性、机制及其对污染物吸附的研究进展进行了归纳总结:(1)微塑料在环境中经长期老化,其表面变得粗糙不平,部分呈现薄片状脱落,造成比表面积增加,同时在光照、氧气等老化因子作用下,形成羟基、羧基等含氧官能团;此外由于微塑料长期受到老化作用,其聚合物中的长链发生断裂,引起结晶度的变化.(2)微塑料老化过程主要涉及多方面:物理层面上,受到外界剪切力和拉伸力的作用引起聚合物内部的分子链断链,破坏其稳定结构;化学层面上,光氧化降解是其主要的老化机理;生物层面上,通过定殖生物在微塑料表面形成的生物膜引起其物理、化学特性(粗糙度、表面电荷、表面自由能)的变化.(3)微塑料老化后对污染物的吸附能力增强,吸附主要通过范德华力、静电作用、络合作用、疏水作用、氢键等作用方式吸附重金属和有机污染物.未来应加强微塑料在真实自然环境中老化特征及同多种污染物的交互作用的研究,以模型量化表示其内在联系,为科学合理地认识微塑料的环境行为及生态风险评估提供理论依据.

The objective of this review was to summarize the microplastics aging characteristics and mechanisms,and further the adsorption behaviors of pollutants on microplastics were reviewed.The main conclusions were drawn as follows:(1)The microplastic surface would become rougher after long-term aging,accompanying with some pieces flaking and falling off,which resulted in increasing of specific surface area.Meanwhile,the formation of oxygen functional groups such as hydroxyl,carboxyl.was found after exposure to several factors in environments such as oxygen and sunlight.In addition,the long molecular chains of the microplastics were broken due to aging,which altered their crystallinity.(2)Microplastic aging processes could be found as follows:as for physical aspects,the molecular chain in polymers was destructed by the shear and tensile forces externally and thus the stable structure was destroyed.Photooxidation degradation was the main aging mechanism from the aspect of chemical reactions.On the biological level,the physical and chemical characteristics of microplastics such as roughness,surface charge and surface free energy facilitated the biofilm formation on the microplastics by colonizing microorganisms,which then affected the migration behaviors of microplastics in environments.(3)The adsorption capacity of microplastics to pollutants(heavy metals and organic pollutants)could be enhanced after aging,which were mainly affected by van der Waals’force,electrostatic action,complexation,hydrophobic action and hydrogen bond.In the future,we should pay more attention to the study of the aging characteristics of microplastics in complex environments and their interactions with various pollutants.Exploring the relationship between these pollutants quantitatively and using the models provides the theoretical basis of understanding the behavior and assessing the ecological risks of microplastics in environments scientifically and reasonably.