水环境中微塑料与溶解性有机质复合光转化及迁移行为研究

Microplastic (MP) has been widely detected in aquatic environments around the world. Thus, the understanding of the transformation and transport of MP in aquatic environment is the precondition for comprehensively estimating the fate and ecological risks of MP. In aquatic system, the ubiquitous dissolved organic matter (DOM) has been identified to have significant effects on the transport and fate of various contaminant mainly through photochemical and physicochemical pathways. And, MP is proved to be photooxidative and have environmental behaviors as nanoparticles. Thus, it is very likely that DOM would have significant effects on MP’s environmental behavior under sunlight irradiation. This proposal aims to systematically study the hetero-phototransformation and transport of MP-DOM associates, by using several MP and DOM fractions with different physicochemical characteristics. By identifying the key reaction of photo-induced production of reactive intermediates from DOM, and characterizing the variation of physicochemical properties of both MP and DOM, the mechanism of MP-DOM hetero-phototransformation are proposed. Furthermore, the aggregation and transport kinetics of MP-DOM phototransformation products are studied in aquatic phase and saturated porous media. Accordingly, the inherent links among MP and DOM properties with their hetero-environmental behavior would be clarified. The implementation of the project would provide scientific evidences for understanding the fate of MP in environment and scientifically assessing the ecological risks of MP.

微塑料（MP）的水环境污染已呈全球化趋势。深入认识MP在水环境中的迁移转化规律是客观评估其环境风险的前提。水环境中含有丰富的溶解性有机质（DOM），其光化学和物理化学过程对诸多环境污染物的行为和归趋具有重要影响，而MP具有光氧化性和类似纳米颗粒的行为特性，故而DOM极有可能在光照条件下深刻影响MP的水环境行为。本项目拟选用在理化性质上具有代表性的多种MP和DOM组分，模拟研究它们的复合光化学转化和迁移过程。通过识别关键活性中间体反应途径，并结合多种表征技术监测MP和DOM理化性质变化，阐明MP-DOM的复合光转化机制；进一步通过团聚动力学和饱和多孔介质迁移实验研究复合光转化过程对二者协同迁移行为的影响。从而揭示MP/DOM理化性质与二者复合环境行为的内在关系。项目的实施可为深入认识MP环境归趋和科学评估其生态风险提供科学依据。

随着在全球水体中的广泛检出，微纳塑料污染已成为地表水环境中最严峻的生态问题之一。先前研究已表明，水体中的天然有机质（NOM）可与多种纳米颗粒发生理化及光化学作用，介导纳米颗粒转化。那么，NOM是否会影响纳塑料的光老化过程及迁移行为成了迫切需要回答的科学问题。.为探究NOM对纳塑料光老化过程的影响、识别介导纳塑料光老化的关键组分，本项目对广谱NOM进行了按分子量分级，研究了它们在聚苯乙烯（PS）纳塑料上的吸附行为，并利用三维荧光-平行因子分析法探究了二者复合光老化过程中NOM特征荧光组分的变化。结果显示，分子量越大的NOM组分在纳塑料上吸附量越大；纳塑料粒径越小对相同NOM组分的吸附能力越强；在复合光老化过程中，粒径较小的纳塑料加剧了各分子量NOM组分中类胡敏酸物质的光降解，说明这些荧光团发生了显著的电荷转移过程，均可加剧小粒径纳塑料的光老化过程；而对于粒径较大的纳塑料，可能仅有小分子量NOM显著加剧了老化过程。.为对比NOM对纳塑料光老化前后理化性质及在水环境中迁移行为的影响，通过模拟了多种干预条件下的极性聚甲基丙烯酸甲酯（PMMA）和非极性PS纳塑料光老化前后理化性质和团聚行为的变化；并探究了PS纳塑料与不同分子量NOM组分的异质性团聚行为。结果显示：NOM 介导的光老化使PMMA表面含氧官能团增多，但zeta电势降低且颗粒间黏连程度升高，PMMA-NOM复合光老化产物在 NaCl和CaCl2 中稳定性变差，临界絮凝浓度分别降低至原始PMMA样品的62%和56%。而对于PS纳塑料，单独光老化后表面含氧官能团也增多，zeta电势升高，稳定性在NaCl体系中更好，但是在CaCl2体系中变差；此外，高分子量NOM组分通过空间位阻效应可以有效削弱PS纳塑料在NaCl体系中的团聚，但却由于CaCl2将其与PS纳塑料形成桥连，从而促使其与PS纳塑料在CaCl2体系中的异质性团聚行为加剧。.本项目初步阐明了不同分子量NOM组分中介导PS纳塑料光老化的主要组分，对比了NOM对不同单体纳塑料光老化和迁移行为的影响。相关结果与结论可为深入认识纳塑料的环境行为提供数据支持。