Road-runoff Pollution in English Surface Drains: Chemical Composition and Potential Associated Environmental Risk(s)

Rivers and other surface waters worldwide receive thousands of chemicals from diverse sources, including road runoff. We identified more than 170 chemicals that have been associated with road runoff across published literature that derive from tyre wear, exhaust emissions, and brake pad abrasion, amongst other sources. The impact of these chemicals on aquatic organisms however is poorly understood. Addressing this knowledge gap for U.K. surface drains, we first analysed the available literature studies on road run-off (23) to determine the concentrations of 70 chemicals in road run off monitored in surface drains by the U.K. Environment Agency over 25 years (between the years 2000 and 2024). We show 43 of the 70 monitored chemicals in U.K. surface drains exceed reported minimum concentrations and 19 the highest measured concentrations across existing literature. Twenty of the monitored chemicals exceeded the lowest effect concentration for 50% lethality (LC50) in fish and/or aquatic invertebrates. These findings suggest that road-runoff chemicals in U.K. surface drains pose a potential risk to aquatic life, but their impacts will depend upon other factors including their dilution levels in rivers.