Assessment of Microplastics in the Surface Water of Mengkabong and Salut Rivers of Sabah, Malaysia

Microplastics in river water are a global risk to aquatic ecosystems due to their longevity in the environment, causing toxicity, ingestion by organisms, and bioaccumulation. However, knowledge and research on microplastic pollution are still scarce in Sabah, Malaysia, as no studies have been carried out before. Hence, this study aimed (1) to determine the occurrence of microplastics in the surface water of the Mengkabong and Salut Rivers in Sabah and (2) to assess the spatial variability in the concentration and characteristics of microplastics within these rivers. Microplastics were extracted, counted, and characterized for their shape, colour, size, and polymer. An independent t-test was used to compare microplastic abundance and characteristics between the two rivers, whereas Hierarchical cluster analysis was used to group the eight stations based on similarities in microplastics. This study detected microplastics at all stations, with a significantly higher concentration (p < 0.05) of microplastic in the Salut River (4.78±2.43 items/L) compared to those in the Mengkabong River (1.63±0.87 items/L). Fibre was the most abundant microplastic shape in both Mengkabong (78%) and Salut (57%), likely sourced from textile washing, fishing, and aquaculture activities in the vicinity. Transparent microplastics were prevalent in Mengkabong (30%), while black microplastics dominated in Salut (42%). Size distribution exhibited the opposite trend, with 74% larger-sized microplastics in Mengkabong but 63% smaller-sized microplastics in Salut. Polymer analysis revealed rayon (68%) dominance in Mengkabong, while polyethylene (34%) and rayon (33%) in Salut. Spatial heterogeneity of microplastics was evident through cluster analysis, categorizing stations into clean, moderately polluted, and polluted. Stations adjacent to areas with fewer land-based activities were clean with a low microplastics count, while areas with intense developments, residential, and fishing activities were polluted with high microplastic counts. This study underscores the presence of microplastics in Sabah's rivers, serving as a foundational reference for future research. It is also imperative to conduct regular monitoring of microplastics in the rivers of Sabah since it is anticipated that microplastics contamination will escalate in the coming years globally.