Synthetic microfibers are ubiquitous in benthic algae from the Laurentian Great Lakes

Synthetic microfibers are a class of microplastics routinely released into environmental media from domestic laundry and wastewater treatment plant effluent. Areas of high human population density discharge immense amounts of synthetic microfibers that pollute and accumulate in sediments, surface waters, algae, and other parts of the ecosystem. Synthetic microfibers are abundant in the Laurentian Great Lakes of North America, but their movement and fate are not well understood. Macroalgae effectively sequester microfibers; however, it is unknown if quantities of synthetic microfibers differ in benthic algae of the Great Lakes based on human population density or algal type (such as Cladophora or charophytes). Presented here is a 4-year study that investigated benthic algae samples from four of the Laurentian Great Lakes: Lakes Michigan, Huron, Ontario, and Erie. Synthetic microfibers were isolated and quantified in the algal samples, and values were analyzed with respect to algal type, lake, and population density. The average estimated number of synthetic microfibers per kg (dry weight) of benthic algae in each lake ranged from 1.6 $\times$ 10⁴ to 2.0 $\times$ 10⁴. Microscopic analysis suggested a possible interaction between epiphytic diatoms and benthic macroalgae (Cladophora), which may help to explain the ability of the algae to sequester microfibers regardless of algal type. The results also suggest a lack of correlation between human population density and number of synthetic microfibers in benthic algae, which could imply facile movement and distribution of microfibers in large bodies of water, that includes the aquatic food web of macroinvertebrates and fish communities.