微塑料胁迫对浮游植物胞外聚合物产生特性及其对含取代基多环芳烃生物有效性的影响

Microplastic, as a emerging environmental contaminant, has been paid more attention among researchers．Previous studies have shown that hetero-aggregation was a key factor for generateing toxicity to phytoplankton, and the extracellular polymeric substances (EPS) play an important role in the formation of heteroaggregates with microplastics. However, the characterization of EPS released by phytoplankton exposed to microplastics stress and the binding interactions of EPS with microplastics have been little investigated. In addition, the role of EPS on the bioaccumulation and biotoxicity of substituted polycyclic aromatic hydrocarbons (S-PAHs) to phytoplankton in the presence of microplastics are not yet clear. In the present study, the binding characteristics of EPS from Prorocentrum donghaiense and Skeletonema costatum to polystyrene microplastics with various size and the effects of homo-aggregaton of microplastics by the EPS will be explored. Subsequently, the effects of the composition of EPS produced by phytoplankton under the stress of microplastics will be studied. Moreover, the adsorption characteristics of pyrene, 1-hydroxypyrene, 1-nitropyrene, 1-aminopyrene and 1-methylpyrene to microplastics will be revealed. The distribution of S-PAHs in the EPS and algae cells will be measured. Finally, the relationship between EPS characteristics with the bioavailability of S-PAHs will be analyzed. The results of this project may be beneficial to the revelation of the fate of EPS, and environmental risk assessment and prevention of microplastics/S-PAHs in aquatic system.

微塑料作为一种新型环境污染物，其环境行为及生态效应越来越受到研究者的重视。已有研究发现异团聚是造成微塑料浮游植物毒性的一个关键前提，且胞外聚合物（EPS）在异团聚过程中其重要作用。目前，尚缺乏微塑料胁迫下浮游植物产生EPS特性及微塑料与EPS相互作用的针对性研究。此外，有关EPS在微塑料胁迫下浮游植物对含取代基PAHs（S-PAHs）生物有效性影响过程尚不明晰。本项目首先考察不同粒径聚苯乙烯微塑料与东海原甲藻和中肋骨条藻产生的EPS间结合特性及EPS对微塑料自团聚影响。其次，探明微塑料胁迫对浮游植物产生EPS特性的影响。最后，考察微塑料对芘、1-羟基芘、1-硝基芘、1-氨基芘和1-甲基芘藻类生物富集和毒性效应影响的基础上，探明微塑料对S-PAHs吸附特性；明确微塑料胁迫下S-PAHs在EPS及藻细胞中的分布；阐明微塑料胁迫下EPS产生特性与S-PAHs生物有效性间关联性。

微塑料作为一种新型环境污染物，其环境行为及生态效应已受到全球学者的极大关注。本项目首先调查分析了浙江省近岸海域表层海水和沉积物中微塑料的丰度、化学成分、形状和颜色等特征；其次，考察了聚苯乙烯微塑料对浮游植物中肋骨条藻毒性效应及其胞外聚合物（EPS）特性影响，结果显示藻细胞生长、光合作用、氧化应激及EPS中溶解性有机碳、单/多糖和荧光组分特征的变化与微塑料浓度，尺寸和电荷有关。再次，在了解了水溶态芘/芘衍生物荧光光谱特性的基础上，利用荧光分析结合分子动力学模拟研究了聚苯乙烯微塑料与芘/芘衍生物（1-甲基芘、1-羟基芘、1-羧基芘及1-氨基芘）间吸附行为及机制，结果表现为-CH3在一定程度上促进了吸附，而-OH、-NH2和-COOH的存在阻碍了芘衍生物在聚苯乙烯微塑料上的吸附。聚苯乙烯微塑料对芘及其衍生物的吸附容量随其粒径减小而增大；盐度和温度对PS微塑料与芘及其衍生物间的吸附行为影响与芘环上的取代基有关；疏水作用、π-π相互作用和孔隙填充是聚苯乙烯微塑料与芘/芘衍生物间主要吸附机制。最后，通过多角度（中肋骨条藻生长、光合作用、氧化应激及转录组等）研究了聚苯乙烯微塑料对芘/芘衍生物（1-甲基芘、1-羟基芘、1-羧基芘及1-氨基芘）生物有效性的影响，结果表明在芘/芘衍生物浓度为12 μg/L时，除1-羧基芘外，其余3种芘衍生物对中肋骨条藻的毒性效应同样高于芘；聚苯乙烯微塑料对芘/芘衍生物生物毒性的降低效果与芘环上的取代基有关；与对照组相比，微塑料存在组中肋骨条藻的差异表达基因数目均高于各自芘/芘衍生物单独暴露组。本研究结果可为深入了解海洋环境中微塑料及含取代基多环芳烃（S-PAHs）环境行为及生态毒性提供了科学依据，对正确掌握微塑料及S-PAHs风险评价及管控提供一定基础数据和理论依据。