Effects of cold-climate environmental factors temperature and salinity on benzotriazole adsorption and desorption in bioretention cells

Abstract

Benzotriazole, a common anti-corrosion additive in vehicle antifreeze products, is a polar contaminant frequently detected in urban runoff, particularly in cold seasons. Urban low impact development systems such as bioretention cells have shown promise to mitigate traditional stormwater contaminants. However, to date, their efficiency to reduce pollution by polar trace organic chemicals is unclear. In this study, the adsorption and desorption potential of benzotriazole to bioretention soil and hardwood mulch was investigated at varying temperature and salinity levels. The lower organic matter quality of bioretention mulch than soil, likely due to the dominance of lignin in the former and proteins in the latter, resulted in a higher affinity of benzotriazole on soil than mulch. The adsorption capacity increased with decreasing temperature. The low enthalpy changes of −5.6 (soil) and −14 kJ/mol (mulch) suggested adsorption via van der Waals forces and dipole-dipole interactions, respectively. Conversely, changes in salinity showed little effect on the adsorption of benzotriazole. Desorption was observed for both bioretention substrates, but was lowest at low benzotriazole concentrations. Altogether, despite low to moderate adsorption coefficients, these results showed that bioretention cells are able to retain benzotriazole particularly in cold climate conditions.