Urban tributaries identified as major sources of plastic chemical pollution in the Yangtze River

A new study reveals that urban tributaries flowing through Wuhan are significant sources of phthalate esters, a widely used class of plastic chemicals, to the Yangtze River, highlighting previously underestimated risks to aquatic ecosystems in one of the world’s largest river systems.

Phthalate esters, often abbreviated as PAEs, are chemicals commonly added to plastics to make them flexible and durable. They are found in everyday products ranging from packaging and construction materials to personal care items and medical devices. Because these chemicals are not chemically bound to plastics, they can easily escape into the environment during use and disposal. Many PAEs are known to disrupt hormones and pose ecological risks, raising growing concerns about their presence in rivers and sediments.

In the new research, scientists conducted a comprehensive field investigation of the Yangtze River and eight of its tributaries in the Wuhan section, a densely populated and economically important region in central China. Water and sediment samples were collected during both dry and wet seasons, allowing the team to examine how pollution levels change over time and how contaminants move between sediments and the water column.

The results show that tributaries play a much larger role in PAE pollution than previously recognized. Concentrations of PAEs were consistently higher in tributaries than in the Yangtze River mainstream, particularly during the dry season. During the wet season, overall concentrations increased across both tributaries and the main river, likely driven by rainfall, runoff, and increased transport of pollutants from urban surfaces.

“Our findings clearly demonstrate that urban tributaries are not just passive channels,” said corresponding author Zulin Zhang. “They are active and significant contributors of plastic chemicals to the Yangtze River, especially in highly urbanized areas.”

The study identified five dominant PAEs in both water and sediment, including compounds widely regulated due to their toxicity. These chemicals accounted for the vast majority of total PAE contamination across all sites and seasons. Importantly, the researchers found strong evidence that river sediments act not only as sinks but also as ongoing sources of pollution. Under certain conditions, PAEs stored in sediments can be released back into the water, prolonging exposure for aquatic organisms even if external inputs are reduced.

“This secondary release from sediments is particularly concerning,” Zhang explained. “It means that historical pollution can continue to affect river water quality long after the original sources are controlled.”

Ecological risk assessments conducted in the study indicate that PAEs in river water pose medium to high risks to sensitive aquatic organisms, while risks associated with contaminated sediments are consistently high. Among all detected compounds, one commonly used plasticizer emerged as the most hazardous in both water and sediment environments.

In contrast, the assessment found no significant health risks to humans under current exposure scenarios. Estimated non-carcinogenic and carcinogenic risks for different age groups were all below established safety thresholds. While this suggests limited immediate danger to people, the authors caution that ecological impacts and long-term accumulation remain serious concerns.

The study underscores the importance of managing pollution at its sources. Rather than focusing only on large river channels, effective control strategies must also address smaller urban tributaries, where contamination is often more concentrated and directly linked to human activities.

“Protecting major rivers like the Yangtze requires a system-wide perspective,” Zhang said. “Targeted monitoring and pollution control in urban tributaries will be critical for reducing ecological risks and safeguarding freshwater ecosystems.”

The research provides new scientific evidence to support more comprehensive river management strategies in rapidly urbanizing regions, both in China and worldwide.

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Journal reference: Xie F, Wu M, Chen Y, Gao S, Yin C, et al. 2025. Spatiotemporal distribution, migration behaviors, and ecological risks of phthalate esters in tributaries and mainstream of the Yangtze River, Wuhan section. Environmental and Biogeochemical Processes 1: e015 doi: 10.48130/ebp-0025-0015   

https://www.maxapress.com/article/doi/10.48130/ebp-0025-0015  

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About the Journal:

Environmental and Biogeochemical Processes (e-ISSN 3070-1708) is a multidisciplinary platform for communicating advances in fundamental and applied research on the interactions and processes involving the cycling of elements and compounds between the biological, geological, and chemical components of the environment. 

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