Which pollutant is most commonly associated with urban runoff?

Sediment is the pollutant most commonly associated with urban runoff due to several factors inherent in urban environments. Urban areas often undergo significant land use changes, which can expose bare soil and disrupt the natural landscape. When it rains, the flow of water can easily transport sediment from construction sites, roads, and other disturbed areas into nearby water bodies.

This sediment not only serves as a carrier for other pollutants, such as nutrients and heavy metals but also can lead to increased turbidity in water bodies, which affects aquatic life and can degrade water quality. Furthermore, sediment can smother aquatic habitats and disrupt the balance of ecosystems.

Nutrients, heavy metals, and bacteria are certainly important pollutants associated with urban runoff, but they are often more of a concern in specific contexts or scenarios, whereas sediment is a ubiquitous issue resulting from the very nature of urban development and land alteration. Therefore, sediment emerges as the most common pollutant in discussions regarding urban runoff and its environmental impacts.