Tracing Plastic from Farms and Cities to the Sea: Inside China’s Mulan River Crisis

A study by the Asian Development Bank shows how everyday plastic waste in China’s Mulan River Basin is washed from land into rivers and eventually the ocean, with solid waste and agricultural plastics as the main sources. It demonstrates that treating plastics as a regulated pollutant within river basin management can significantly reduce plastic leakage to the sea.

Plastic pollution is often imagined as a problem of distant oceans and floating debris, but its origins are far closer to home. A recent Asian Development Bank (ADB) brief shows how everyday plastic use on land is steadily carried into the sea through rivers. Prepared by ADB's Agriculture, Food, Nature, and Rural Development Sector Office, with research published by academic partners in Water Research, the study focuses on China's Mulan River Basin to reveal, step by step, how local plastic waste becomes a global environmental threat.

A Global Crisis with Local Roots

Worldwide, plastic production has passed 460 million tons a year, and about 14 million tons end up in the oceans annually. Scientists estimate that roughly 170 trillion plastic particles are already circulating in marine environments. Over time, large plastic items break down into microplastics that persist for centuries, carry toxic chemicals, and enter food chains. While global negotiations are underway to curb plastic pollution, one major problem remains: policymakers often lack clear evidence showing where plastics come from and how they travel from land to water.

Why the Mulan River Matters

The Mulan River, in Fujian Province in the People's Republic of China, offers a clear example. The river runs about 105 kilometers from the mountains of Xianyou County through Putian City before reaching the sea. Over the past 40 years, the area has changed rapidly. Urbanization increased from just over 11% in the early 1980s to more than 63% by 2020. With more roads, packaging, delivery services, and plastic-intensive farming, waste has grown quickly. Heavy seasonal rainfall from the region's monsoon climate then washes plastic from land into drains and rivers.

Following Plastic through the River Basin

To understand this process, researchers built a model that tracks plastic waste across the entire river basin between 2010 and 2020. The model combines information on land use, population, economic activity, rainfall, and river flow. It follows plastic from several sources: household and commercial solid waste, agricultural plastic films used in farming, plastics from roads and other hard surfaces, and domestic sewage. The model also separates direct discharge points, such as wastewater treatment plants, from diffuse pollution that enters rivers during storms. When tested against real monitoring data, the results closely matched what was observed in the river.

What the Numbers Reveal

The findings show how small, scattered sources add up. Each year, the Mulan River Basin generates about 313 tons of plastic waste. Most of it stays on land at first, but rainfall eventually carries part of it into the river system. On average, around 35 tons of plastic reach the river annually, and about 23 tons flow all the way into the ocean. Solid waste is the largest contributor, responsible for nearly 38% of river pollution. Agricultural plastic films account for about 26%, plastics from roads and other impermeable surfaces account for about 22%, and microplastics from sewage around 13%. The message is clear: plastic pollution is not driven by a single source, but by everyday activities spread across cities, villages, and farms.

Turning Evidence into Action

The study argues that plastics should be treated as a "new pollutant" within river basin management, just like nutrients or chemicals. This thinking is already shaping action in the Mulan River Basin. A $548.6 million ADB-supported program running through 2028 is expanding wastewater treatment, improving solid waste collection and recycling, promoting biodegradable agricultural plastics, and investing in local recycling industries. Digital monitoring systems and public awareness campaigns aim to change behavior alongside infrastructure.

The larger lesson goes beyond one river. Plastic pollution may be global, but it is built from local decisions about how waste is produced, managed, and regulated. The Mulan River shows that when plastics are tracked carefully from land to sea, the problem becomes clearer and more solvable. Stopping plastic from reaching the ocean, the study suggests, must begin upstream, one river basin at a time.