Spatio-temporal distribution of microplastics in water and sediment samples of the Plankenburg river, Western Cape, South Africa

Microplastic (MPs) pollution has become a subject of environmental concern due to its wide ubiquity in the environment. Microplastics are possible sources of other hazardous chemicals to aquatic organisms due to their composition and sorption properties. In this study, MPs occurrence in water and sediment samples of the Plankenburg River, Western Cape, South Africa was investigated. The physicochemical characterization of the river water was done onsite. 30 L water samples were collected and filtered in 10 L triplicates through a 250 mu m mesh onsite using a metal bucket. An additional 12 L sample was collected and filtered in 4 L triplicates through 20 mu m mesh in the laboratory. The extraction of MPs from water in the laboratory was by density separation. Sediment samples were also collected at the selected sites, oven-dried and microplastics in the laboratory. Sampling was conducted over four seasons - spring, summer, autumn, and winter. Microplastics were classified by visual observation and Fourier Transform Infrared Spectroscopy (FTIR-ATR). The seasonal distribution of MPs in the surface water samples varied across all sites. However, spring samples had the highest MPs occurrence (5.13 +/- 6.62 MP/L) and the least, in autumn (1.52 +/- 2.54 MP/L). The MPs in sediment samples were observed in spring (1587.50 +/- 599.32 MP/kg). Fibres were the most dominant microplastic particle type (shape), with a size range of 500-1000 mu m at the different sites. The infrared spectroscopic analysis confirmed the dominant polymer type to be polyethylene. This study provides an understanding of the microplastic occurrence in the Plankenburg River system and gives a baseline for future monitoring and assessment of water and sediment in the South African freshwater systems.

Automated summary

This study investigated the occurrence of microplastics in water and sediment samples of the Plankenburg River in Western Cape, South Africa. The results showed variation in the distribution and seasonal occurrence of microplastics in the samples, providing a baseline for future monitoring and assessment of freshwater systems in South Africa.