Pollutant Transformation in Urban Road Surfaces: Implications for Stormwater Reuse

The significance of stormwater as a viable alternative for overcoming freshwater shortages in urban areas has been widely recognized. Stormwater with suitable quality can be utilised for different ‘fit-for-purposes’. However, the prevalent use of stormwater has become a challenge due to the declining stormwater quality from toxic pollutants such as metals and hydrocarbons. These pollutants, primarily accumulate on urban impervious surfaces such as roads during dry weather periods, and eventually washed-off and transported by stormwater runoff to receiving waterways. Prior to entraining into stormwater runoff, pollutants undergo different transformation processes, in which their physical and chemical forms undergo dynamic changes, resulting in changes to their persistence, mobility, toxicity and bioavailability characteristics. These transformation processes can be influenced by the physicochemical properties of road dust particles, the primary adsorbents of pollutants, and prevailing environmental conditions. It can be considered that the deterioration of stormwater quality is not only influenced by the presence of toxicants, but also the transformations that they undergo during dry weather periods. This is because of the variability in mobility, bioavailability and toxicity of transformed pollutants can exert a significant impact on stormwater quality compared to their original form. Stormwater quality enhancement should therefore be undertaken in a way that the transformation processes of pollutants are thoroughly understood.