A Comprehensive Methodology for Estimating Yearly Plastic Pollution Loads in Rivers

Abstract

Abstract Plastic pollution in freshwater systems represents a major global concern, as rivers serve as critical pathways between land-based sources and marine environments. Yet, inconsistencies are observed between estimated plastic inputs from land and concentrations in the ocean. Despite growing monitoring efforts, the lack of standardized methods and the use of diverse metrics for quantifying plastic pollution hamper direct comparisons across studies and limit comprehensive assessments. In this study, we developed a method for quantifying yearly macro- and mesoplastic load, incorporating different metrics. By integrating statistical analysis, the method accounts for variability in plastic concentrations and discharge rates. Subsequently, this methodology was applied to the Rhine and Meuse rivers in the Netherlands. The findings of this study indicate a spatial variability in plastic concentrations. The mean annual load of macro- and mesoplastics (items > 0.5 cm) in the Rhine was highest at Lobith, located at the Germany–Netherlands border (331 million items/year), decreasing downstream to 206 million items/year at Tiel. Similarly, in the Meuse, higher loads were observed at Eijsden, at the Belgium–Netherlands border (73 million items/year), than further downstream at Sambeek (62 million items/year), while particles in the 5–6 mm size range are likely underrepresented due to the 6 mm mesh size of the sampling net. Correspondingly, the mean annual surface area load of macro- and mesoplastics in the Meuse showed a downstream decrease, with mean values declining from 71,641.63 m 2 /year at Eijsden to 30,714.92 m 2 /year at Sambeek. The methodological approach enables the quantification of plastic loads, providing important insights into the dynamics of plastic pollution in river systems. This allows for predictions of future plastic quantities in the Rhine-Waal and Meuse rivers under different emission scenarios and measurement units.