水动力介导下微塑料影响藻毒素环境行为的复合机制

Microcystins can be produced and released by some of the toxin-producing harmful algae species and its bioavailability are closely linked to its behavior at the solid-water interface in aquatic environment. Microplastics, which are defined as small plastic fragments with size <5 mm, are widely reported in freshwaters in China. The microplastics are characterized as small size, huge specific surface area and hydrophobicity, making them a carrier for microcystins. In this study, with the purpose of interpreting how microplastic influence the environmental behavior of microcystins, we devoted to study the linkage between hydrodynamics alternation, surface property of microplastic and the environmental behavior of microcystins under mesocosm scales, according to the annual hydrodynamics alternation in Yulin River, a tributary in Three Groge reservoir. From the perspective of “source” induction and “sink” transformation, the environmental scanning electron microscope and high-throughput sequencing technology were employed to study the impact of hydrodynamics coupled with microplastic on the environmental behavior of microcystins, including 1) the response of microcystin-producing capability of cyanobacteria in response to microplastic exposure, 2) the micro-interface processes of how the microplastic absorb microcystins, 3) the development of biological film attached on microplastic as well as its relationship with environmental fate of microcystins, and 4) the migration of microcystins from water to microplastic and sediment. The results of this study are supposed to improve our understanding on the environmental risk of microplastics, and are helpful for assessing the ecological risk of the combined pollution of microplastics and microcystins.

藻毒素是产毒藻细胞的代谢产物，其在水环境中的生物有效性与其在颗粒物-水界面的行为密切相关。我国淡水环境中广泛存在的微塑料（粒径<5mm的塑料）具有粒径小、比表面积大、疏水等特点，易成为藻毒素的载体。针对"微塑料影响藻毒素环境行为"这一命题，以三峡库区次级河流-御临河在蓄泄水周期内的水动力参数为依据，本研究围绕水动力学特征、微塑料表面特性及藻毒素环境行为，采用环境扫描电镜和微生物高通量测序等分析手段，从“源”激发至“汇”迁移这一视野出发，通过研究：①产毒藻释毒能力在微塑料暴露下的响应；②微塑料吸附藻毒素的微界面过程；③微塑料附着微生物膜形成的动态规律及其对藻毒素的环境效应；④变化水动力下微塑料影响藻毒素在水-微塑料-沉积物相迁移转化的过程和效应，来解析水动力介导下微塑料影响藻毒素环境行为的复合机制。研究结果有望丰富现有对微塑料环境效应的认识，并可为评估微塑料-藻毒素复合体的生态风险提供依据。

针对微塑料与新污染物的复合风险，本项目系统解析了新生和老化微纳塑料对铜绿微囊藻生长和产毒能力的调控作用、研究了不同种类微塑料吸附藻毒素（MCs）的过程、解析了藻源有机质调控下微塑料吸附MCs的行为过程和关键机制、探索了近似均匀紊流模拟系统中，微塑料对MCs迁移转化的影响过程。发现老化纳米聚苯乙烯塑料对铜绿微囊藻造成了明显的细胞形态损伤,且引起剂量正相关的生长、光合抑制、氧化损伤，并促进了微囊藻毒素（MC-LR）的合成和释放；聚苯乙烯（PS）、聚乙烯（PE）、聚甲基丙烯酸甲酯（PMMA）对MCs的吸附平衡时间均为24 h，达到吸附平衡后，PS对MCs的吸附容量最大，可达到843 μg/g，而PE和PMMA对MCs的最大吸附容量分别为722和521 μg/g。在藻源有机质存在的条件下，PE、PS和PMMA对MCs的最大吸附容量分别为558、655和493 μg/g，分别下降了22.3%、22.7%和5.4%，说明藻源有机质抑制了微塑料对MCs的吸附。在模拟紊动体系中，添加了生物抑制剂的体系MCs的浓度无显著变化。添加20 mg/L的PS体系中，MCs浓度较实验初始降低了9%。去除叠氮化钠对生物的抑制后，体系中有PS时，MCs的去除率上升至35.8%，在静止状态下（20 mg/L PS，无叠氮化钠），水体中MCs的去除率为24.9%。而当体系中无PS时，MCs的去除率为28.2%。在未添加叠氮化钠的处理体系的质谱图中，均出现MCs裂解的典型中间体Adda（m/z=331），证明MCs发生了生物降解过程。此外，在水体和微塑料表面都检测到了MCs降解菌的存在，进一步证实了MCs存在生物降解过程。表明在水体扰动体系中，微塑料可通过吸附、“微塑料圈”的生物降解等作用影响水体中MCs的降解过程。