微塑料对土壤典型持久性有机污染物生物有效性的影响及机制研究

Plastic has been the most important material for human life and industrial production. Large-scale production and massive consumption of plastics have led to the worldwide accumulation of plastic wastes both in the ocean and on the land. Due to their durability and refractory to biodegradation, plastics can remain in the environment for many years, while their physical breakdown leads to the formation of small plastic particles, including microplastics. As a class of emerging contaminants, microplastics are a global environmental concern. While numerous studies have described the occurrence and adverse effects of microplastics in the aquatic environment, relatively little is known about their fate and effects in the terrestrial environment, even though large amounts of microplastics enter soil via a multitude of routes. This proposal aims to investigate the effects of microplastics on the bioavailability of persistent organic pollutants in soil. Briefly, microplastics with different polymers and different soils will be selected. PAHs and PCBs will be chosen as the typical contaminants in soil. The change of sorption characteristics of the soils will be investigated after amendment with microplastics and aged microplastics. In addition, the freely dissolved concentration, bioaccessibility, and bioaccumulation of the contaminants will be investigated in the soils amended with microplastics. The implement of the project will provide a scientific basis for the risk assessment of microplastics in the soil environment and food chain, which is of great importance for both academic research and real applications.

塑料已成为现代生活和产生不可或缺的一种生产材料，而其造成的微塑料污染已经成为新型环境问题受到全球的重视。当前对微塑料的研究多集中于水域生态系统，而作为微塑料重要的源头和主要汇集地，很少有研究涉及到土壤中微塑料污染。微塑料进入土壤后可改变土壤性质，进而影响有机污染物在土壤中的环境行为。本项目旨在研究微塑料对土壤持久性有机污染物生物有效性的影响。拟分别选取不同成分的微塑料颗粒和不同性质的土壤，通过研究有机污染物吸附行为特征，探索土壤添加微塑料及环境老化微塑料后吸附特性变化，识别影响污染物生物有效性的主要因素；系统研究微塑料颗粒对土壤有机污染物的间隙水浓度、生物可利用度以及生物积累的影响，探明微塑料影响生物有效性的机制。项目的实施可揭示土壤微塑料对有机污染物的传递规律，为建立微塑料土壤生态风险评价和食物链风险评估提供科学依据。

土壤环境是微塑料最大的聚集汇和水环境微塑料的重要来源。由于微塑料粒径小、比表面积大、疏水性较强，其在土壤环境中可以作为一种较强的吸附介质而影响土壤中有机污染物的环境行为。但与水环境中的研究相对比，很少有研究涉及到土壤中微塑料是否能够作为载体影响污染物在土壤动物中的积累。对此，项目设计了多种暴露模式，包括污染微塑料进入干净土壤环境以及干净微塑料进入污染土壤环境，研究这一过程中蚯蚓积累疏水性有机污染物的变化。同时考虑到微塑料在环境中会进一步破碎而形成更小颗粒的事实，课题组探讨了微塑料颗粒大小是否对微塑料载体起到关键影响作用。研究表明微塑料与污染物之间的平衡状态是决定微塑料增加或减少污染物积累的关键，而微塑料对整个积累的贡献则与微塑料颗粒大小相关。研究表明蚯蚓暴露于预先污染的微塑料与干净的土壤环境中，微塑料携带的污染物可被蚯蚓吸收。蚯蚓积累系数在污染微塑料+干净土壤的暴露下（S2），要小于其暴露于干净微塑料+污染土壤（S1）。这一结果表明，HOCs在微塑料上的生物有效性要小于其在土壤中的有效性。这是由于在静态环境中，HOCs与微塑料之间的分配平衡要远远慢于HOCs与土壤颗粒之间的分配。造成S2暴露情景下HOCs在土壤间隙水中的浓度要低于S1。随着微塑料粒径逐渐降低，微塑料的载体作用逐渐增大，这一结果表明在实际环境中随着微塑料的不断破碎，其对HOCs的吸附吸收会逐渐增强，从而增加了其在污染物积累中的作用。且微塑料粒径减小也会进一步增加其被土壤动物吞食的风险，造成的危害会更严重。