Heavy rainfall drives microplastic pollution in rivers

Southeast and East Asia accounted for more than half of the estimated global river flow in 2022.(CN) — Heavy rain can send bursts of microplastics surging through rivers and into the ocean, with developing countries carrying the vast majority of the world’s river-borne pollution, new research suggests.Rivers worldwide delivered an estimated 263,000 tons of microplastics to the ocean in 2022, according to researchers.About 96% came from the Global South, with Southeast and East Asia together accounting for more than half of the total.The findings, publishedThursday in the journal Science, highlight how rainfall can quickly change the amount of plastic moving through rivers. Extreme downpours can wash large amounts of microplastics into waterways, particularly in places with high plastic use and poor waste management.That could become a growing problem as climate change makes extreme rainfall more frequent and intense, researchers warn.Microplastics, tiny plastic particles that persist in the environment, have become widespread pollutants with risks to ecosystems, water quality and human health. Tens of millions of metric tons enter the environment each year, and rivers provide an important route for carrying the particles from inland areas to the ocean.However, scientists have faced challenges when attempting to estimate how much microplastic rivers carry worldwide.Studies use different sampling methods and measure particles of different sizes, making results difficult to compare. Scientists also have not fully understood how rainfall and runoff affect the amount of plastic moving through rivers.Hehao Qin and colleagues developed a new framework aimed at providing more consistent estimates. Their approach accounted for differences in sampling methods and particle sizes and used machine learning to consider both human activity and natural processes.They also examined how rainfall changes microplastic concentrations. Rain can have competing effects, either washing more plastic into waterways or diluting the concentration already in the water.Using the framework, researchers found that human activity played the biggest role in determining where microplastic concentrations were highest. Plastic use, poorly managed waste and human development were the strongest drivers of differences from one region to another, while weather and seasonal conditions had a greater influence on shorter-term changes.The results also showed that heavy rainfall can substantially increase the movement of microplastics into rivers. The effect was especially pronounced in areas where large amounts of plastic are used and waste management systems are inadequate.That connection between rainfall and pollution could make some regions increasingly vulnerable to sudden spikes in microplastics.Rather than pollution entering waterways at a steady rate, extreme storms can produce short-lived periods when particularly high concentrations are flushed into rivers and eventually marine environments.The findings also point to a stark geographic divide.Although microplastic pollution is a worldwide problem, researchers estimated that developing regions account for nearly all of the material carried by rivers into the ocean. Southeast and East Asia alone contributed more than half of the estimated global total in 2022.Researchers say the results could help provide a clearer picture of where river-borne microplastic pollution is coming from and how changing weather patterns influence when it reaches the ocean.With extreme rainfall expected to become more frequent and intense as the climate changes, the researchers warn those pollution surges could also become more common, creating “short-lived but highly concentrated pollution pulses into rivers and marine environments.”Subscribe to our free newslettersOur weekly newsletter Closing Arguments offers the latest about ongoing trials, major litigation and rulings in courthouses around the U.S. and the world, while the monthly Under the Lights dishes the legal dirt from Hollywood, sports, Big Tech and the arts.Additional Reads