Evaluation of the Barcelona urban soil capacity for retention of emerging contaminants

The fate of emerging contaminants from runoff/storm waters in urban areas has aroused widespread concern as it poses a threat to the water managing. Contaminated water can reach, for instance, the river that passes through the area, contributing to the degradation of the aquatic ecosystem, or the aquifer that supplies drinking water to the community. In this framework, one of the objectives of the URBANWAT project is to evaluate the capacity of the Barcelona urban soil to retain the contaminants of emerging concern from runoff waters in order to propose an improvement of tools and criteria for groundwater management in urban areas.

To this aim, a set of batch and packed soil column experiments were performed. The soil selected for the study is located in the Barcelona urban area at 20 m depth and composed of 48 % quartz, 28 % albite and 24 % microcline. It is constituted by 91 % sand, 7 % silt and clay and 2 % gravel, being the sand particle size dimension the one selected to perform the column experiments. The resident water in contact with the soil was analysed by ICP-MS and has a conductivity of 723 µS/cm and pH of 7.9. A list of representative emerging contaminants has been selected from diverse pharmaceutical families and UV filters based on the concentration values found in the runoff waters of the Barcelona urban area.

The batch experiments were carried out first to verify if the soil already contained the target contaminants and second to know the soil sorption capacity. The target contaminants have different properties (pka, charge) that cause them to be sorbed with variable efficiency by the soil tested (80-100 % sorption for Paroxetine and Venlafaxine, 60-80 % for Cocaine and Caffeine, 40-60 % for Tradadol and Climbazole and low sorption (< 40 %) for a list of more than 15 emerging contaminants). Sorption capacities obtained in the batch experiments were also identified in the percolation tests, obtaining significantly different breakthrough curves for the studied target contaminants. By means of the percolation column experiments, the effect of the flow rate on the soil retention capacity was evaluated and the two main processes involved in the pollutants retention mechanism (sorption and biodegradation) were quantified to verify the specific contribution of each process to the global procedure.