Quantification, characterization, and source identification of macro- and mesoplastics on the riverbanks of Rivers...

Rivers are a significant conduit for land-derived plastic litter to the ocean, bridging terrestrial and marine environments. Yet, even though they are a primary pathway, much of the plastic entering river systems is retained along the river courses. This necessitates sampling various river sections, including riverbanks, to comprehend the distribution of plastic litter in these areas. Plastic litter along the riverbanks of Rivers Sabaki and Tana in Kenya was assessed over an annual cycle. Monitoring was done in two replicates at various preselected riverbank types, to assess their contribution to retention of plastic litter. Factor and cluster analyses were used to identify the sources of plastic litter. A total of 8793 plastic litter items weighing 65.38 kg, and 8429 plastic litter items weighing 85.08 kg were cataloged at Rivers Sabaki and Tana, respectively. Apart from whole items, plastic fragments were among top-ten litter types. The plastic litter densities in River Sabaki ranged from 0.06 to 2.17 items/m², with a mass range of 0.40-25.96 g/m². River Tana exhibited a density range of 0.12-0.70 items/m², with a mass range of 1.40-8.96 g/m². On seasonal variation peak accumulation of plastic litter was observed in December 2021 for River Sabaki, and in January 2022 for River Tana. Factor and cluster analysis revealed potential sources of plastic litter at River Sabaki including: recreational activities, direct littering, dumping from informal settlements, agricultural activities, and upstream sources. For River Tana, identified sources were: illegal dumpsites, direct littering, upstream sources, fishing, and navigation activities. The insights from this research could aid policymakers combat riverine plastic pollution, ultimately benefiting the ocean.