Microplastic abundance and accumulation behavior in Lake Onego sediments: a journey from the river mouth to pelagic waters of the large boreal lake

Contamination of bottom sediments with microplastics (MPs) was first studied in Lake Onego - the second largest lake in Europe. The studied region is the most populated part of the lake watershed and covers the estuarine part of a large river (Shuya River), the Petrozavodsk Bay and the pelagic part of the lake. The mean MPs concentration in the sediment was 2188.7 +/- 1164.4 pieces per kg of dry weight. It is two times higher than the same in The Baltic Sea and is comparable with highly urbanized areas of the world. Possible reasons for such a high rate of MPs accumulation in Lake Onego can be due to both the proximity to their sources and accumulation behavior. MPs spatial distribution exhibited a predictable pattern along the transsection from the river mouth to pelagic waters. Fibers were the most abundant form comparing with other fractions (61 +/- 13 % of the total), however different MPs shapes prevailed in various regions. Relationship between MPs content in sediment and physical and chemical sediment characteristics was established. Fibers accumulation is related to the medium silt fraction (0.01-0.05 mm) and indicates the presence of the major accumulation zones for MPs.