Pollutant Distribution on Urban Surfaces: Case Study in Southern Brazil

Urban development, in addition to causing changes in the hydrological cycle, increases the amount of pollutants as the result of anthropogenic factors such as land use, local activities, and regional traffic. This study aimed to quantify pollutants related to sediments of different sizes on impermeable surfaces. The knowledge that the amount of various pollutants is associated with sediment size is important in the design of treatment facilities capable of removing most of the polluted sediments. The study region is the Cancela Basin, located in Santa Maria, Brazil. Pollutants were quantified in relation to the various sizes of sediments on the impervious surfaces of streets having similar levels of urbanization but different traffic intensities and gradients. Dry sediment samples collected prior to rainfall and surface runoff sediment samples collected during rainfall were separated into four granulometric bands ($\le 63\mathrm{\mu m}$, 63–250 μm, 250–500 μm, and $\ge 500\mathrm{\mu m}$). Organic pollution and nutrient and heavy metal contents were evaluated for each granulometric band. Heavy metals were more concentrated in samples representing granulometry levels $\le 63\mathrm{\mu m}$. In the dry sediment samples, the chemical oxygen demand (COD) and phosphate contents were found in samples representing granulometry levels $\ge 500\mathrm{\mu m}$. Ammonia, nitrates, lead, and zinc were associated with the 63–250 μm granulometric band.