Abundance and composition of microplastics in surface sediments of three selected rivers in south-western Nigeria Oluwatosin Shokunbi 1,2 , Gideon Idowu 2 , Festus Aiyesanmi 2 1 Department of Basic Sciences, Babcock University, Nigeria, 2 Department of Chemistry, Federal University of Technology Akure, Nigeria The occurrence of microplastics (MPs) in aquatic environments is of huge concern around the globe. This is due to the environmental, economic and health risks of this emerging contaminant. This study investigated the abundance, composition of MPs, heavy metals (HMs) and surface sediment characteristics (pH, conductivity, organic matter, available nitrogen, available phosphorus, and percentage sand, silt and clay) of three selected rivers in Southwestern Nigeria. Surface sediments were collected from Ogun, Odo-Ona and Osun rivers using a stainless-steel trowel. The MPs from the sediments were inspected for shapes, colour and size, using an optical microscope, while the polymer types were identified by Fourier transform infrared (FTIR) spectroscopy. The sediments’ physicochemical characteristics were determined using standard methods. The concentration of HMs (As, Cd, Cr, Cu, Mn, Ni, Pb, V, and Zn) in sediments was determined by inductively coupled plasma-mass spectrometry (ICP-MS). The abundance of MPs (items/kg dry weight) ranged from 56.67 - 311, 200 - 500, and 133 - 433, for the Ogun, Odo-Ona, and Osun rivers, respectively. Fibres were the dominant microplastic form, followed by fragments and films. The colours of the MPs were mostly red, blue, and black, while the size of the fibre and fragment particles were between 30 µm and 5 mm. Polyethylene and polypropylene polymers constitute the majority of the materials of the MPs found. All the analysed heavy metals were detected in sediments and microplastics, with Cr, Cu, Mn, V and Zn being the most abundant. Heavy metals in microplastics were highest in Odo-Ona River, Oyo State. Conductivity (27.3 – 279 µS/cm), organic matter (0.06 – 5.92 %), available nitrogen (0.05 – 0.38 %) and available phosphorus (5.1 – 11.02 %) were all positively and significantly correlated ( p < 0.05) with microplastic abundance in the sediments the three rivers. The presence of microplastics and HMs in the three rivers poses great risks to the ecosystem and human health.
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© The Author(s), 2023
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