Are microplastics increasingly invading rivers near cities and farmland?

A river in the Colombian Andes reveals growing pollution from microplastics, especially where human activity is intense. Researchers examined the presence of these tiny particles in the water, sediments, riverbanks, and even in the fish of the Combeima River basin. Their finding is clear: the further downstream toward urban and agricultural areas, the more microplastics are found.

Fibers, often from synthetic textiles or polymer blends such as polypropylene, dominate the waste found, particularly in fish. Water and aquatic animals contain more microplastics than soils or sediments, where larger particles tend to accumulate. Scientists identified a wide variety of plastics, including polyester, high-density polyethylene, and other materials linked to clothing or industrial packaging.

The study also shows that seasons influence their distribution. During heavy rains, runoff carries more microplastics into the river, while in the dry season, they accumulate more in the sediments. Downstream areas, near cities and cultivated land, have the highest concentrations, confirming that human activity accelerates this pollution.

To understand their origin, researchers analyzed the chemical composition of the particles. They found that blue fibers, often from clothing, are the most widespread, followed by fragments of various colors, likely from degraded plastic packaging or objects. Fish, as a key link in the food chain, ingest these particles, posing a risk to all aquatic biodiversity.

Riverbanks and sediments act as reservoirs, trapping the heaviest microplastics, while lighter ones remain suspended or are swallowed by animals. The shape and size of the particles vary depending on their source: fibers mainly come from textiles, and fragments from broken plastic waste.

This research highlights a problem that is still understudied in tropical freshwater ecosystems. It underscores the importance of monitoring these pollutants, whose presence depends on land use, urban discharges, and the natural dynamics of waterways. The findings help better target actions to limit contamination and protect aquatic environments, which are essential for both nature and local populations.

Credits and Attributions

Primary Source

DOI: https://doi.org/10.1007/s10750-025-06095-7

Title: Microplastic abundance and composition along an anthropogenic pressure gradient in an Andean river (Colombia)

Journal: Hydrobiologia

Publisher: Springer Science and Business Media LLC

Authors: A. Prado-Guasca; F. A. Villa-Navarro; E. O. López-Delgado; V. A. Arana-Rengifo; G. Guevara-Cardona