Divergent Transport\nDynamics of Alkylated versus Unsubstituted\nPolycyclic Aromatic Hydrocarbons at the Air–Water and Sediment-Water\nInterfaces at a Legacy Creosote Site

Alkylated polycyclic\naromatic hydrocarbons (PAHs) are\nabundant\nconstituents of many PAH mixtures and contribute to risk at contaminated\nsites. Despite their abundance, the movement of alkylated PAHs remains\nunderstudied relative to unsubstituted PAHs. In the present study,\npassive sampling devices were deployed in the air, water, and sediments\nat 11 locations across multiple seasons to capture spatial and temporal\nvariability in the abundance and movement of alkylated PAHs at a Brownsfield\ncreosote site in Oregon, USA. Freely dissolved concentrations of 18\nalkyl homologous series were quantified by gas chromatography-triple\nquadrupole mass spectrometry. Alkylated PAHs were consistently more\nabundant than unsubstituted PAHs in all sampled media (sum PAH and\nAPAH concentrations 43–96% alkyl PAHs). Models of diffusive\nand advective flux revealed abundant 2 and 3-ring alkyl PAHs exhibited\nseasonal differences in movement, particularly across the air–water\ninterface. The novel application of these methods to freely dissolved\nalkylated PAH homologues revealed that, in many instances, alkylated\nPAHs, particularly C3 and C4 homologues, moved in the opposite direction\nas unsubstituted PAHs across both the air–water and sediment-water\ninterfaces. These findings reinforce the need to characterize alkylated\nPAHs and seasonal variability and can inform future sampling at contaminated\nsites.