Rivers may be delivering far more microplastic pollution to the oceans than previously realized, with developing countries accounting for nearly all of the global flow, according to a new study. The worldwide analysis also finds that heavy rainfall can unleash surges of microplastics into rivers – a climate-sensitive pollution threat that could intensify as extreme weather becomes more common. Microplastics have become a pervasive and long-lasting form of pollution, with recognized threats to ecosystems, water quality, and human health. Each year, tens of millions of metric tons of microplastics enter the environment, and much of that material ultimately reaches the oceans. Rivers are a major pathway for transporting these particles from inland regions to coastal waters. However, estimates of global riverine microplastic pollution vary widely because of inconsistent sampling methods and limited understanding of how rainfall and runoff affect their transport. Here, Hehao Qin and colleagues developed a new framework to produce more reliable, high-resolution estimates of microplastic concentrations and export from rivers. According to the authors, their approach harmonizes differences in particle size and sampling methods, while using machine learning to account for both human activity and natural processes. It also tracks how rainfall can either increase or dilute microplastic concentrations. Using this approach, Qin et al. estimate that rivers worldwide delivered roughly 263,000 tons of microplastics to the ocean in 2022, with 96% originating from the Global South – Southeast and East Asia alone contribute to more than half of this total. Plastic use, poorly managed waste, and human development were the strongest drivers of geographic differences in microplastic concentrations, while weather and seasonal conditions influenced short-term fluctuations. The findings show that extreme rainfall events can substantially increase the movement of microplastics into rivers, particularly in regions with high plastic use and poor waste management. Qin et al. warn that climate change could worsen this problem as extreme rainfall becomes more frequent and intense, potentially creating short-lived but highly concentrated pollution pulses into rivers and marine environments.

Peking University, September 24, 2026: Rivers around the world carried about 260,000 metric tons of microplastics into the ocean in 2022, according to a new study led by researchers at Peking University (PKU). Published in Science, the study finds that this pollution is not released at a steady rate throughout the year. Instead, heavy rainfall and floods can trigger short, concentrated surges of microplastic transport.

Applied Microbiology International (AMI) has responded to the European Commission’s consultation on the proposed EU Ocean Act, highlighting the essential contribution of marine microorganisms to ocean health, climate regulation, biodiversity and the blue bioeconomy.