Microplastic accumulation in endorheic river basins – The example of the Okavango Panhandle (Botswana)

• Published in: The Science of the total environment Vol. 874; p. 162452
• Main Authors: Kelleher, Liam, Schneidewind, Uwe, Krause, Stefan, Haverson, Lee, Allen, Steve, Allen, Deonie, Kukkola, Anna, Murray-Hudson, Mike, Maselli, Vittorio, Franchi, Fulvio
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 20.05.2023
• Subjects: Botswana; data collection; ecosystems; Endorheic basin; environment; fluorescence microscopy; Microplastics; Okavango; oxbow lakes; Panhandle; poly(vinyl chloride); polypropylenes; polystyrenes; Raman spectroscopy; rivers; sediment contamination; Sediments; watersheds; wetlands; Botswana; Panhandle; Microplastics; Endorheic basin; Sediments; Okavango
• ISSN: 0048-9697; 1879-1026; 1879-1026
• DOI: 10.1016/j.scitotenv.2023.162452

The Okavango Panhandle is the main influent watercourse of the Okavango Delta, an inland sink of the entire sediment load of the Cubango-Okavango River Basin (CORB). The sources of pollution in the CORB, and other endorheic basins, are largely understudied when compared to exorheic systems and the world's oceans. We present the first study of the distribution of microplastic (MP) pollution in surface sediments of the Okavango Panhandle in Northern Botswana. MP concentrations (64 μm-5 mm size range) in sediment samples from the Panhandle range between 56.7 and 399.5 particles kg−1 (dry weight) when analysed with fluorescence microscopy. The concentrations of MP in the 20 μm to 5 mm grain size range (analysed with Raman spectroscopy) range between 1075.7 and 1756.3 particles kg−1. One shallow core (15 cm long) from an oxbow lake suggests that MP size decreases with depth while MP concentration increases downcore. Raman Spectroscopy revealed that the compositions of the MP are dominated by polyethene terephthalate (PET), polypropylene (PP), polyethene (PE), polystyrene (PS), and polyvinyl chloride (PVC). From this novel data set it was possible to estimate that 10.9–336.2 billion particles could be transported into the Okavango Delta annually, indicating that the region represents a significant sink for MP, raising concerns for the unique wetland ecosystem. [Display omitted] •Microplastic concentration in sediment of Okavango Delta ranges from 56.7 to 1756.3 particles per kg dry weight.•Upscaling of Okavango MP concentration suggests endorheic basins represent significant plastic sink.•PET, PVC and PE were identified as most abundant polymer types.•MP concentrations were not related to sediment grain size or percentage of silt and clay.