The\nFate of Microplastics in Rural Headwater Lake\nCatchments

In this study, the fluxes of microplastics\n(mp) were quantified\nduring a 12-month period for three rural headwater lake catchments\nin Muskoka-Haliburton, south-central Ontario, Canada. A novel catchment\nparticle balance approach was used, incorporating inputs from atmospheric\ndeposition and stream inflows against lake outflow and sedimentation.\nThis approach provides the first reported observation-based estimates\nof microplastic residence time in freshwater lakes. Atmospheric deposition\nhad the highest daily microplastic flux (3.95–8.09 mp/m<sup>2</sup>/day), compared to the inflow streams (2.21–2.34 mp/m<sup>2</sup>/day), suggesting that it is the dominant source of microplastics\nto rural regions. Approximately 44–71% of the deposited microplastics\nwere retained in the terrestrial catchments and 30–49% of the\nmicroplastics in the stream inflows were retained in the study lakes.\nGiven that output fluxes ranged from 0.72–3.76 mp/m<sup>2</sup>/day in the sediment and 1.18–1.66 mp/m<sup>2</sup>/day in\nthe lake outflows, the microplastic residence time was estimated to\nbe between 3 and 12 years, suggesting that lakes are an important\nreservoir for microplastics. Fibers were the dominant shape in atmospheric\ndeposition, streamwater, and lake water; however, in lake sediment,\nthere was a higher proportion of fragments. Across all media, poly(ethylene\nterephthalate) was the dominant polymer identified (23%).