Key Laboratory of Watershed Sciences and Health of Zhejiang Province, School of Public Health and Management, Wenzhou Medical University, Wenzhou 325035, China; Fujian Institute of Oceanography, Xiamen 361013, China.
Key Laboratory of Watershed Sciences and Health of Zhejiang Province, School of Public Health and Management, Wenzhou Medical University, Wenzhou 325035, China; State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen 361102, China.
Water Res. 2022 Jul 15;220:118656. doi: 10.1016/j.watres.2022.118656. Epub 2022 May 24.
Sinking of microplastics (MPs) after biofouling is considered an important mechanisms responsible for the downward transport/sedimentation of MPs in the ocean and freshwaters. Previous studies demonstrated MP sinking caused by an increase in the composite density of MPs after biofouling, while MPs with smaller size or shapes with higher surface area to volume ratios (SA:V), such as films, are speculated to sink faster. In this study, we designed an in situ microcosm to simulate the ambient environmental conditions experienced by floating MPs to elucidate the biofouling and sinking of polyethylene (PE), polypropylene (PP), and expanded-polystyrene (EPS) MPs of various sizes and shapes. Our results showed smaller PE and PP MP granules sank faster than large ones. Even EPS granules of 100 μm diameter, having a much lower density (0.02 mg/mm) than water, started to sink after 2 weeks of biofouling. Moreover, PE film and fiber MPs with higher SA:V did not sink faster than PE MP granules of the same mass, implying that mechanisms other than SA:V, such as fouling contact area and drag coefficient, play a role in the regulation of biofouling and sinking of MPs.
生物污损后微塑料（MPs）的下沉被认为是导致海洋和淡水中 MPs 向下传输/沉降的重要机制。先前的研究表明，生物污损后 MPs 复合密度的增加导致 MPs 下沉，而尺寸较小或比表面积与体积比（SA:V）较高的形状，如薄膜，据推测下沉速度更快。在这项研究中，我们设计了一个原位微宇宙来模拟漂浮 MPs 所经历的环境条件，以阐明各种尺寸和形状的聚乙烯 (PE)、聚丙烯 (PP) 和膨胀聚苯乙烯 (EPS) MPs 的生物污损和下沉。我们的结果表明，较小的 PE 和 PP MP 颗粒比大颗粒下沉得更快。即使是直径为 100 μm 的 EPS 颗粒，密度（0.02 mg/mm）比水低得多，在生物污损 2 周后也开始下沉。此外，具有更高 SA:V 的 PE 薄膜和纤维 MPs 并不比相同质量的 PE MP 颗粒下沉得更快，这表明除了 SA:V 之外的其他机制，例如污损接触面积和阻力系数，在调节 MPs 的生物污损和下沉中发挥作用。
