Lake-wide assessment of microplastics in the surface waters of Lake Baikal, Siberia

Small microplastic particles < 330 µm, sometimes called mini-microplastics (MMP), are far more abundant than those larger than 330 µm. These smaller particles pose the greatest ecological risk to aquatic organisms, but have seldom been quantified in the surface waters of lakes or water bodies with long residence times where neutrally buoyant microplastics can accumulate. We quantified microplastics (MP) ranging in size from 20 µm to 5 mm in the surface waters (1 m depth) of the three basins of Lake Baikal, Siberia, which has a residence time of 377–400 years. Average lake-wide MP concentration equaled 291 ± 252 m−3, with MMP comprising 88% of total MP abundance. Our average MP concentration was 100–1000 × greater than those reported previously for L. Baikal, most likely because our methods allowed the quantification of MMP. Highest MP concentration in L. Baikal occurred in Maloe More Strait where tourism is most concentrated. MP fragments (in contrast to fibers) and the plastic polymer, polypropylene, were numerically dominant in L. Baikal, suggesting that the major source of MP is fragmentation of plastic debris. A review of the literature and our results revealed that residence time is an inadequate predictor of MP concentration in lakes, and that MP contamination has likely been vastly underestimated in many N. American and European lakes. Investment in solid waste and wastewater management infrastructure as well as the enforcement of anti-pollution laws are urgently needed to reduce plastics entering L. Baikal.