Freshwater plastic pollution is critically understudied in Southeast Asia (SEA). Recent modelling studies indicate that SEA rivers contribute vast quantities of plastic to the world’s oceans, however, these fail to capture the complexity of individual systems. We determine the volume of mismanaged plastic waste (MPW) entering Tonle Sap Basin (TSB)—the largest freshwater lake–river system in SEA, between 2000 and 2030. Using economic, population and waste data at provincial and national levels, coupled with high resolution population and flood datasets, we estimate that ca. 221,700 tons of plastic entered between 2000 and 2020, and 282,300 ± 8700 tons will enter between 2021 and 2030. We demonstrate that policy interventions can reduce MPW up to 76% between 2021 and 2030. The most-stringent scenario would prevent 99% of annual MPW losses by 2030, despite substantially higher waste volumes and population. If successfully implemented, Cambodia will prevent significant losses in natural capital, material value and degradation in TSB worth at least US$4.8 billion, with additional benefits for the Mekong River and South China Sea.

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Spectroscopic analysis has become an essential part of the rapidly growing field of microplastic (MP) research. Here we introduce a simple sample preparation method which dramatically improves results from Fourier Transform Infrared (FTIR) analysis of MP and other environmental fibres. Our method provides cost-effective, reliable, high-quality spectra that achieve high-matching scores to polymer libraries. The efficacy of this method is demonstrated with two environmental datasets from Singapore and Phnom Penh that were collected while sampling for atmospheric MPs. The method developed and applied in this study is a simplification of the KBr method, where the analysed fibre is pressed to a thickness of <10 μm, however no KBr powder is required. For the combined dataset, 379 non-pressed fibres were analysed with 193 (51%) returning a Search score of ≥80% (chosen minimum Search score threshold), and 259 pressed fibres, with 254 (98%) returning a Search score of ≥80%. Direct comparisons of fibres before and after pressing show that the highest individual Search score, and average Search score from multiple single-point measurements, are overwhelmingly higher following our method. Our method immobilises and improves the surface of the fibre, by creating a wider and uniform area for measurements to be taken. For FTIR operators, this saves considerable time, improves reliability of the analysis, and importantly, provides reproducibility of the spectra generated.

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