Microplastic abundance and distribution in the open water and sediment of the Ottawa River, Canada, and its tributaries

Microplastic pollution is prevalent in the Ottawa River, with all open water samples ( n = 62) and sediment samples ( n = 10) containing microplastics. The median microplastic concentration of nearshore 100 L water samples was 0.1 fragments per L (ranged between 0.05 and 0.24 fragments per L). The larger volume Manta trawls samples taken in the middle of the Ottawa River had an overall mean concentration of plastics of 1.35 fragments per m 3 . Plastic concentrations were significantly higher downstream of the wastewater treatment plant (1.99 fragments per m 3 ) compared with upstream of the effluent output (0.71 fragments per m 3 ), suggesting that the effluent plume is a pathway for plastic pollution to the Ottawa River. The mean concentration of microplastic fragments recovered in the sediment samples was 0.22 fragments per g dry weight. The abundance of microplastics in the sediment was not significantly related to the mean particle size or the organic content of the sediment. The most common form of plastic particles found was microfibers. These made up between 70% and 100% of all plastic particles observed, although plastic microbeads and secondary plastic fragments were also recovered.