Rainwater, as it flows over urban surfaces (such as roads, rooftops, or recreational areas), carries with it numerous pollutants that have accumulated in these areas. If left untreated, these pollutants are discharged into aquatic ecosystems.

A study coordinated by the Catalan Institute for Water Research (ICRA), the University of Barcelona (UB), and the University of the Basque Country (EHU) (CityPoll project; https://citypoll.eu/) analyzed urban runoff water, identifying a long list of pollutants. Among the most notable are heavy metals and compounds derived from tire wear, which were found in high concentrations. It has been shown that this urban runoff affects aquatic organisms, impacting their growth, reproduction, and vital functions, which may have serious consequences for the functioning of freshwater ecosystems connected to urban drainage networks.

The study found significant differences between areas within the same city, as well as between rainfall events, making the detection and analysis of urban runoff more complex. It also assessed the effectiveness of green filters as mitigation structures for these impacts. Based on the results, the researchers propose using diphenylguanidine—a chemical marker associated with tire wear—as an indicator of pollution from urban runoff. The study also emphasizes that the complete separation of stormwater and urban wastewater collection systems is essential to minimizing the impact of these pollutants. Likewise, the need to promote nature-based mitigation structures as treatment measures for urban runoff water is highlighted.

In a context of climate change, where rainfall is less frequent but more intense, the effects of urban runoff pollution may worsen, placing even greater stress on affected aquatic ecosystems. For this reason, it is essential to minimize its impact by adapting our urban systems accordingly.