Urban tributaries identified as hidden drivers of plastic chemical pollution in the Yangtze River

Plastic associated chemicals known as phthalate esters are widespread in rivers worldwide, but their sources and environmental risks are not always easy to trace. A new study focusing on the Wuhan section of China’s Yangtze River reveals that urban tributaries play a much larger role in driving this pollution than previously recognized, particularly during seasonal changes.

Researchers analyzed water and sediment samples from the Yangtze River and eight of its tributaries across both dry and wet seasons. They detected sixteen different phthalate esters, chemicals commonly used to make plastics flexible and durable in products such as packaging, medical devices, construction materials, and personal care items.

The results show that tributaries flowing through urban and industrial areas consistently contained higher concentrations of phthalates than the main river channel. During the dry season, these tributaries acted as concentrated sources that fed pollutants into the Yangtze River. During the wet season, overall contamination increased across the entire river system due to rainfall, runoff, and sediment disturbance.

“Our findings clearly show that tributaries are not just passive channels,” said corresponding author Zulin Zhang. “They are active contributors of phthalate pollution to the Yangtze River, especially in densely populated and industrialized areas.”

Among the detected compounds, five phthalates dominated both water and sediment samples. These included dimethyl phthalate, diethyl phthalate, di n butyl phthalate, diisobutyl phthalate, and bis 2 ethylhexyl phthalate. Together, they accounted for more than 95 percent of the total phthalate burden measured in the study.

The research also revealed an important hidden process. River sediments were not simply storing these chemicals but were releasing them back into the water under certain conditions. This secondary release was particularly pronounced in tributaries during the wet season, when stronger flows and higher temperatures can disturb sediments.

“Sediments behave like a long term reservoir for phthalates,” Zhang explained. “Even if inputs from the surface are reduced, contaminated sediments can continue to release these chemicals into the water, prolonging ecological exposure.”

To assess potential impacts, the team evaluated ecological and human health risks. They found that phthalates in river water posed medium to high risks for sensitive aquatic organisms such as algae and invertebrates. Sediments consistently showed high ecological risk levels, with bis 2 ethylhexyl phthalate emerging as the most hazardous compound in both water and sediment.

In contrast, the study found no significant human health risk from direct exposure to river water under current conditions. All calculated non carcinogenic and carcinogenic risk indices remained below established safety thresholds for different age groups.

“This does not mean the problem can be ignored,” said Zhang. “Ecological risks are already evident, and protecting aquatic life is essential for the long term health of the entire river system, including human communities that depend on it.”

The study highlights the need for pollution control strategies that go beyond monitoring major rivers alone. Effective management must also address urban tributaries and contaminated sediments, particularly in rapidly developing regions.

By identifying when and where phthalate pollution is most severe, the research provides critical scientific evidence to support targeted monitoring, improved wastewater management, and more effective regulation of plastic associated chemicals in large river systems.

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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  

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

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About the Journal:

Environmental and Biogeochemical Processes 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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