Estimation of macroplastic yield from river basin to coastal area: A case study of the Klang River, Malaysia

Plastic pollution in aquatic ecosystems has become a critical global environmental challenge, threatening biodiversity, water quality, and human health. This study investigates macroplastics distribution and characterization in the highly polluted Klang River, Malaysia, and proposes a protocol to compute total macroplastic yield in the river basin. A total of 240 macroplastic items were collected over a 20-km stretch from the river mouth inland, with an average of 0.91 ± 0.80 g/item (dry weight). Scanning Electron Microscopy revealed that the macroplastics had weathered slowly in the environment, potentially breaking down into smaller microplastic particles. Biofilms and dead phytoplankton were observed on the plastic surfaces, suggesting that plastic debris may act as vectors for other pollutants. The study used SWAT modelling to simulate physical processes in the Klang River Basin and compute pollutant loads through a loading computation procedure. A macroplastic rating curve was created using river discharge, macroplastic loadings, and associate parameters to estimate plastic loading in the river. The fitted equation models macroplastic loading as a function of river discharge and width, expressed as: log(y) = 1.88216-7.36528log(x) - 4.00491log(x²). Here, log(x) represents the ratio of river discharge to river width, while log(y) denotes macroplastic loading adjusted for sampler width and river width. Results indicated that macroplastic transport in the river system is linked to flow rates and sediment yield, which vary due to topographical factors, with an estimated macroplastics yield in the Klang River Basin of 11,600 kg/day. The findings suggest that a river-specific monitoring programs should be conducted to generate comprehensive datasets, integrating both macroplastics and microplastics abundance, which can be utilized for projecting plastic emissions from Malaysian rivers and comparing data with other river basins in the Southeast Asia.