A global study shows that heavy rainfall increases the transport of microplastics via rivers
Rivers around the world discharged approximately 263,000 tonnes of microplastics into the oceans in 2022, with 96 per cent of this originating from the Global South. This is the main finding of a study that has analysed various data sources showing that extreme rainfall events can substantially increase this transport of microplastics, particularly in regions with high plastic use and poor waste management. The authors, whose findings are published in Science, warn that climate change could exacerbate the problem as extreme rainfall becomes more frequent and intense.
Roberto Rosal - plásticos ríos
Roberto Rosal
Professor of Chemical Engineering in the Department of Analytical Chemistry, Physical Chemistry and Chemical Engineering at the University of Alcalá
The article is of high scientific quality and contains significant methodological innovations regarding the estimation of global plastic emissions via rivers. Specifically, and in comparison with previous models such as that of Meijer et al., it presents a very broad empirical basis supported by a large number of direct observations. Whilst Meijer et al. had already demonstrated that plastic pollution reaches the ocean from inland sources via many rivers and not just a few, the authors of this article introduce the temporal variable by considering pulse-like transport induced by episodes of extreme rainfall, which lends their estimates a high degree of physical realism.
The authors estimate that rivers discharge just over a quarter of a million tonnes of microplastics (particles smaller than 5 mm) into the ocean, a figure equivalent to approximately a quarter of the one million tonnes per year estimated by Meijer et al. for floating plastic litter consisting mainly of larger items. This close correlation suggests, on the one hand, that the transport of larger plastics is physically retained within the catchment due to riparian vegetation or sediments, and, on the other hand, the significant contribution from direct sources of microplastics and millimetre-sized particles, which are effectively transported during floods.
The resolution of the analytical framework makes it particularly interesting, although it retains significant uncertainties: chiefly the conversion of numerical concentration (particles per cubic metre) to mass, based on the assumption that the weight of individual particles follows a log-normal statistical distribution, and the reduced physical interpretability inherent in statistical machine learning models. The results confirm that 96 per cent of riverine microplastic emissions originate from the Global South, with South-East and East Asia accounting for more than half of the total load. The study concludes that, unless the overproduction of plastics is curbed and waste management is rapidly improved, rainfall events will continue to drive the discharge of microplastics from rivers into the ocean. Any reference to climate change is unavoidable at present.
Qin et al.
- Research article
- Peer reviewed
