Microplastic occurrence and densities in small subtropical reservoirs of Southern Africa

Microplastics (MPs) pollution is now a global concern and particles have been detected in various aquatic environments and their associated biota including in humans. Its only recent that research in MPs have gain a better understanding of MPs sources, transportation and sink including potential impacts. To further contribute to the growing body of literature, this study aims to quantify and enumerate seasonal MPs densities and characteristics in sediments and surface water samples in small subtropical reservoirs associated with different landscape and human activities. Moreover, the study not only quantified and characterised MPs but further assessed the risk of MPs contamination using pollution load indices. High MPs densities were found during the dry season in sediments (84.74–374.76 particles/kg−1 dwt) and surface water (6.07–21.77 particles/100–1 L), in comparison with low densities in the wet season i.e. sediments (68.72–260.87 particles/kg−1 dwt) and surface water (7.33–19.27 particles/100–1 L). White (43.1%) and transparent (38.4%) colours were the most dominant in sediments and surface water samples, respectively. In terms of MPs shapes and polymer types, fibres and polyethylene (PE) were the most dominate for sediments and surface water. Moreover, no correlative relationships were observed for tested water quality parameters and MPs densities within and between reservoirs and seasons. MPs pollution indices indicated high pollution levels in reservoirs associated with high human activities, indicating a source-driven effect of anthropogenic activities on MPs contamination. This study contributes to understanding the seasonal variations in MPs occurrence and characteristics in small subtropical reservoirs. Additionally, the study establishes a benchmark for future plastic pollution control and management efforts in South African small reservoirs, since if left unattended MPs pollution could escalate and pose significant environmental risks in the future.