Export of Plastic Debris by Rivers into the Sea

TLDR

Rivers serve as a major transport pathway for marine plastic debris originating from land-based sources. The study aims to quantify river plastic loads and evaluate how predictors beyond mismanaged plastic waste, such as hydrological conditions, could improve estimates. By compiling global river plastic debris data and applying mismanaged plastic waste as a predictor, the authors estimated river inputs to the sea at 0.41–4 × 10⁶ t y⁻¹. Plastic loads increase nonlinearly with mismanaged plastic waste, with large, densely populated rivers disproportionately contributing, and the ten largest rivers export 88–95 % of global riverine plastic, though limited data yield high uncertainty.

Abstract

A substantial fraction of marine plastic debris originates from land-based sources and rivers potentially act as a major transport pathway for all sizes of plastic debris. We analyzed a global compilation of data on plastic debris in the water column across a wide range of river sizes. Plastic debris loads, both microplastic (particles <5 mm) and macroplastic (particles >5 mm) are positively related to the mismanaged plastic waste (MMPW) generated in the river catchments. This relationship is nonlinear where large rivers with population-rich catchments delivering a disproportionately higher fraction of MMPW into the sea. The 10 top-ranked rivers transport 88-95% of the global load into the sea. Using MMPW as a predictor we calculate the global plastic debris inputs form rivers into the sea to range between 0.41 and 4 × 106 t/y. Due to the limited amount of data high uncertainties were expected and ultimately confirmed. The empirical analysis to quantify plastic loads in rivers can be extended easily by additional potential predictors other than MMPW, for example, hydrological conditions.