Assessing microplastic characteristics and abundance in the sediment and surface water of the Diep River, Western Cape, South Africa

Rivers play a vital role in the water cycle and serve as habitats for numerous species and potentially contributing to microplastic pollution in the ocean. The Diep River is an important habitat for numerous species bordered by various ecological zones. However, it also presents a risk and pathway for microplastic pollution that can enter the ocean. This study investigated variations in microplastics particle concentrations in water and sediment samples from five locations in the Diep River. Water samples (100 L) were screened onsite using a 250 μm mesh, while an additional 20 L of water samples were filtered through a 20 μm mesh in the laboratory. Additionally, 20 g of sediment samples were collected for analysis at a depth of 5-10 cm from each site and characterised with a combination of visual and FTIR techniques. Fibres were found to be the most dominant shape at all the sites, DR-1 (95.80 %); DR-2 (88.2 %); DR-3 (75.0 %); DR-4 (72.0 %); and DR-5 (93.1 %). The black/grey (47 %) colour and 500-2000 μm (66 %) size categories were the most prevalent for all sites. FTIR analysis showed that polyethylene (52 %) and polystyrene (20 %) were the most abundant polymer types. The microplastic burden was higher in tourist and recreational areas than non-tourist areas. The MP Pollution Load Index (PLI) in the Diep River showed moderate contamination for all sites except DR 2, which has no water flow and therefore no values in autumn. This study offers new insights into microplastic contamination in South Africa's surface water.