Interaction mechanisms between polycyclic aromatic hydrocarbons (PAHs) and organic soil washing agents

Understanding interaction mechanisms between polycyclic aromatic hydrocarbons (PAHs) and soil-washing agents can help in choosing efficient agents which are able to desorb and solubilize PAHs. This study investigated interaction mechanisms between pyrene and four washing agents including: two dissolved organic matters (DOM) F-DOM and CRC-DOM, and two commercial bio-based surfactants BBE-1000 and Supersolv using fluorescence spectroscopy combined with multivariate curve resolution alternating regression (MCR-AR). The efficiencies of these washing agents in removing PAHs from the soil were tested in a soil washing experiment. Pyrene showed π-π interactions with F-DOM and no interaction with CRC-DOM. This could be attributed to the more aromatic structures in F-DOM compared to CRC-DOM. The two DOMs were inefficient in soil washing which might be attributed to the relatively weak effect of π-π interactions in releasing PAHs from the soil. Interaction mechanisms between pyrene and the bio-based surfactants were elucidated with MCR-AR, which resolved three spectroscopically active species from pyrene emission spectra as a function of pyrene and bio-based surfactants concentrations. These species resembled pyrene emission in a polar and nonpolar microenvironment, respectively and of an excimer. Concentration profiles retrieved by the model for the three species showed that, below the critical micelle concentration (CMC), Supersolv created more nonpolar interactions with pyrene compared to BBE-1000. In soil washing, Supersolv showed the highest efficiency in extracting PAHs from the soil. This highlighted the importance of nonpolar interactions in desorbing PAHs from soils, which could then be solubilized in micelles. This study demonstrated the potential of fluorescence spectroscopy combined with the MCR-AR model for selecting efficient soil-washing agents.