A quantitative analysis of microplastic pollution along the south-eastern coastline of South Africa

•No significant difference in microplastic contamination between sites.•More than 90% of samples comprised of blue/black fibres.•No primary microplastics were found in the present study.•Beach densities ranged from 688.9 ± 348.2 to 3308 ± 1449 particles·m− 2.•Water column densities were between 257.9 ± 53.36 to 1215 ± 276.7 particles·m− 3.

The extent of microplastic pollution (< 5 mm) in the southern hemisphere, particularly southern Africa, is largely unknown. This study aimed to evaluate microplastic pollution along the south-eastern coastline of South Africa, looking at whether bays are characterised by higher microplastic densities than open stretches of coastline in both beach sediment and surf-zone water. Microplastic (mean ± standard error) densities in the beach sediment ranged between 688.9 ± 348.2 and 3308 ± 1449 particles·m− 2, while those in the water column varied between 257.9 ± 53.36 and 1215 ± 276.7 particles·m− 3. With few exceptions there were no significant spatial patterns in either the sediment or water column microplastic densities; with little differences in density between bays and the open coast (P > 0.05). These data indicate that the presence of microplastics were not associated with proximity to land-based sources or population density, but rather is governed by water circulation.