Impacts of salinity on the dynamics of fine particles and their associated metals during stormwater management

Elevated salinity in stormwater runoff may adversely impact the efficacy of stormwater management practices (SMPs) in intercepting contaminants via changing the stability of suspended particles as well as the fate and transport of their associated contaminants. Field-collected soil samples were employed to characterize the impacts of salinity on suspended particles. Varying concentrations (10 mM to 1000 mM) of chloride salts (NaCl, KCl, MgCl2, and CaCl2) were applied to suspended particle samples to assess the changes in particle size distribution (PSD) and metal desorption from particles. The concentration of fine particles (d < 10 mu m) was higher in samples treated with up to 100 mM monovalent and 50 mM divalent salts (both corresponding to the ionic strength of-0.1 M). This was attributed to the ion attraction to the particle's surface resulting in induced repulsive forces that prevented coagulation. Particle aggregation was observed at higher salt concentrations, associated with ionic strength greater than-0.1 M, due to compression of the double-layer which restrained the repulsive force. Generally, elevated salinities resulted in increased desorption of exchangeable Cr, Fe, Cu, Zn, and Pb, which is likely a combination of cation exchange and formation of aqueous metal complexes. The contributions of complexation and ion exchange were estimated using experimental results and speciation by MINTEQ. This analysis suggested that cation exchange was generally the main contributor, save Pb, though the role of complexation became more important at high salt concentrations. Increased fine particle and dissolved metal fractions could negatively impact the functionality of SMPs, potentially leading to increased media clogging and increased transport of metals to underlying groundwater and downstream water bodies. This study highlights the importance of optimizing the introduction of salts and proper maintenance of SMPs, particularly in locations where applying deicing salts (e.g., NaCl) is a necessary safety measure. (C) 2021 Elsevier B.V. All rights reserved.