Microplastics in freshwater copepods of Lake Baikal

Little is known about the ingestion or retention of microplastic particles (MPs) by freshwater copepods in nature or in the laboratory. Yet copepods dominate zooplankton biomass in large, oligotrophic lakes where they occupy a critical trophic position, shunting energy from the planktonic and microbial food webs to higher trophic levels. We collected pelagic copepods from Lake Baikal, Siberia where the concentration of MPs is high relative to other large lakes with no large, urbanized areas near its shores. We quantified microplastic (MP) ingestion incidence by the copepods and describe the shape, size, color, and polymer composition of ingested MPs. Incidence of MPs was more than 10X higher than that reported for copepods in British Columbia lakes and similar to that for copepods from oceanic sites recognized as hotspots of microplastic contamination. The high incidence value might be due to our detection of the smaller, more abundant MPs which have often gone undetected in other studies. All ingested MPs were either fibers or fragments; mean MP particle size was 65.2±41.9 µm; transparent MPs were most common; and ingested MPs composed of the high-density polymer polyethylene terephthalate (PET) were the most abundant. Our findings emphasize that calanoid copepods are a potential vector for moving MPs into the pelagic food webs of large, oligotrophic lakes and highlight the importance of investigating MP uptake, retention, and effects by freshwater copepods in nature and the laboratory.