Microplastics at\nEnvironmentally Relevant Concentrations\nHad Minimal Impacts on Pelagic Zooplankton Communities in a Large\nIn-Lake Mesocosm Experiment

To assess the potential risks of contemporary levels\nof plastic\npollution in freshwater ecosystems, a large-scale experiment was conducted\nover 10 weeks in a boreal lake at the IISD-Experimental Lakes Area\n(Ontario, Canada). Fragments of common polymers (polyethylene, polystyrene,\nand polyethylene terephthalate), each with distinct colors and buoyancies,\nwere added as a single pulse to seven in-lake mesocosms in equal contributions\nin a range of environmentally relevant nominal concentrations (6–29,240\nparticles/L). Two additional mesocosms with no added microplastics\nwere used as controls. Zooplankton ingested low levels of microplastics\n(mean of 0.06 particles/individual ± SD 0.07) and generally their\ntotal abundance and community composition were not negatively impacted.\nTemporary changes were however observed; total zooplankton abundance\nand abundance of calanoid copepods were temporarily stimulated by\nincreasing nominal microplastic concentrations, and modest, short-term\nreductions in egg production of the cyclopoid copepod Tropocyclops extensus and abundance of copepod nauplii\noccurred. Collectively, these results suggest that microplastics could\nhave complex impacts on zooplankton communities, stimulating some\nspecies while negatively impacting others.