Characterizing Trace Metal Distribution in Urban Stormwater: Focus on Particulate, Colloidal, and Dissolved Fractions in the Lyon Metropole

Urbanization and soil impermeabilization disrupt the natural water cycle, producing stormwater runoff that carries contaminants such as hydrocarbons, trace metal elements (TMEs), and pesticides (Makepeace et al., 1995). These pollutants, originating from urban surfaces, can harm aquatic ecosystems and groundwater. While stormwater management systems have been developed to control runoff hydraulics, their effectiveness in protecting water quality remains underexplored. The role of colloidal fractions and nanoparticles in the dynamics of contaminants in water infiltration structures must be examined in order to better control the risks of groundwater contamination. This study aims to address this by investigating TMEs in two sites.

The critical zone concept, originally applied to natural environments, must be adapted for urban areas where human activities and infrastructure shape biogeochemical processes. This research examines TME behavior in the industrial and residential areas of the Lyon region, which have similar impermeability but different land uses, to assess how these factors influence TME distribution. Initially, stormwater runoff from both sites is broadly characterized, identifying TMEs in total and dissolved forms. This screening helps determine potential environmental risks and differences in pollution loads between industrial and residential sites. By comparing total and dissolved TME concentrations, we can assess whether these elements are bound to particles or remain in the dissolved phase, impacting their mobility and environmental risks.

Using ultrafiltration, the study further explores how TMEs are transported by separating them into different size fractions: particulate (>0.45 µm), colloidal (0.45 µm – 3 kDa), and dissolved (<3 kDa) phases. Special attention is given to the colloidal phase, which plays a critical role in adsorbing and stabilizing contaminants (Sen and Khilar, 2006). Due to their small size and large surface area, colloids are key vectors for contaminant mobility, directly influencing the fate of pollutants in urban environments.

This research contributes to the urban critical zone concept by examining TME behavior across different land uses and size fractions. It fosters interdisciplinary dialogue by addressing biogeochemical processes in urban environments and their interaction with human activities. By evaluating both total concentrations and size distribution, the study provides a comprehensive understanding of TME behavior in urban runoff, advancing efforts to mitigate environmental impacts in sustainable urban development. Through its focus on pollutant fluxes and contaminant distribution, this work supports a systemic approach to managing urban stormwater and improving water quality.

References :

Makepeace, D. K., Smith, D. W., & Stanley, S. J. (1995). Urban stormwater quality: summary of contaminant data. Critical Reviews in Environmental Science and Technology, 25(2), 93-139.

Sen, T. K., et Khilar, K. C., 2006, Review on subsurface colloids and colloid-associated contaminant transport in saturated porous media. Advances in colloid and interface science, 119(2-3), 71-96.