Sequestration of microfibers and other microplastics by green algae, <em>Cladophora,</em> in the US Great Lakes

Daunting amounts of microplastics are present in surface waters worldwide. A main category of microplastics is synthetic microfibers, which originate from textiles. These microplastics are generated and released in laundering and are discharged by wastewater treatment plants or enter surface waters from other sources. The polymers that constitute many common synthetic microfibers are mostly denser than water, and eventually settle out in aquatic environments. The interaction of these microfibers with submerged aquatic vegetation has not been thoroughly investigated but is potentially an important aquatic sink in surface waters. In the Laurentian Great Lakes, prolific growth of macrophytic Cladophora creates submerged biomass with a large amount of surface area and the potential to collect and concentrate microplastics. To determine the number of synthetic microfibers in Great Lakes Cladophora, samples were collected from Lakes Erie and Michigan at multiple depths in the spring and summer of 2018. After rinsing and processing the algae, associated synthetic microfibers were quantified. The average loads of synthetic microfibers determined from the Lake Erie and Lake Michigan samples were 32,000 per kg (dry weight (dw)) and 34,000 per kg (dw), respectively, 2–4 orders of magnitude greater than loads previously reported in water and sediment. To further explore this sequestration of microplastics, fresh and aged Cladophora were mixed with aqueous mixtures of microfibers or microplastic in the laboratory to simulate pollution events. Microscopic analyses indicated that fresh Cladophora algae readily interacted with microplastics via adsorptive forces and physical entanglement. These interactions mostly cease upon algal senescence, with an expected release of microplastics in benthic sediments. Collectively, these findings suggest that synthetic microfibers are widespread in Cladophora algae and the affinity between microplastics and Cladophora may offer insights for removing microplastic pollution. Macroalgae in the Laurentian Great Lakes contain high loads of synthetic microfibers, both entangled and adsorbed, which likely account for an important fraction of microplastics in these surface waters.

全球地表水中存在着数量惊人的微塑料。微塑料的一个主要类别是合成微纤维，它们来源于纺织品。这些微塑料在洗涤过程中产生并释放，由污水处理厂排放，或从其他来源进入地表水体。构成许多常见合成微纤维的聚合物大多比水密度大，最终会在水生环境中沉降。这些微纤维与沉水水生植物的相互作用尚未得到彻底研究，但可能是地表水中一个重要的水生汇。在北美五大湖，大型丝状绿藻（Cladophora）的大量生长形成了具有大面积的沉水生物量，有收集和富集微塑料的潜力。为了确定五大湖丝状绿藻中合成微纤维的数量，2018年春季和夏季在伊利湖和密歇根湖的多个深度采集了样本。在对藻类进行冲洗和处理后，对相关的合成微纤维进行了定量。从伊利湖和密歇根湖样本中确定的合成微纤维平均含量分别为每千克（干重）32000根和每千克（干重）34000根，比之前在水和沉积物中报告的含量高2 - 4个数量级。为了进一步探究这种微塑料的封存情况，在实验室中将新鲜的和老化的丝状绿藻与微纤维或微塑料的水溶液混合物混合，以模拟污染事件。显微镜分析表明，新鲜的丝状绿藻通过吸附力和物理缠结很容易与微塑料相互作用。这些相互作用在藻类衰老时大多停止，预计微塑料会在底栖沉积物中释放。总体而言，这些发现表明合成微纤维在丝状绿藻中广泛存在，微塑料与丝状绿藻之间的亲和力可能为去除微塑料污染提供思路。北美五大湖中的大型藻类含有大量的合成微纤维，包括缠结和吸附的，这可能是这些地表水中微塑料的一个重要组成部分。