Molecular insight into the co-deposition of biomass-burning-smoke dissolved organic matters influencing the...

Owing to the worldwide wildfire, the environmental process of polycyclic aromatic hydrocarbons (PAHs) in soil is inevitably affected by the co-deposition of biomass-burning-smoke dissolved organic matters (BBS-DOMs), which have significantly different molecular characteristics from soil-DOMs. However, to date, the molecular-level interactions among PAHs, BBS-DOMs, and soil remain a significant knowledge gap. Hence, this study used FT-ICR-MS and multi-spectrometers to comprehensively investigate their molecular-level interactions. This study revealed that the binding coefficient, K_d, of PAHs on BBS-DOMs (2.36 × 10⁴∼7.40 × 10⁴ L/kg) was about 100 times that for PAHs binding onto soils (2.07 × 10²∼8.39 × 10² L/kg), owing to the abundant aromatic CHO, CHON, and CHONP molecules of BBS-DOMs, which were responsible for this stronger interaction. Additionally, the spectral index (SUVA₂₅₄) of BBS-DOMs could be effectively used to predict the sorption capacities of PAHs onto DOMs, with the prediction models of log₁₀K_d = 0.0946SUVA₂₅₄+3.969 and log₁₀K_d = 0.0991SUVA₂₅₄+4.006 (r > 0.95, p < 0.01) for phenanthrene and pyrene, respectively. Interestingly, though BBS-DOMs input (0.1 wt%) significantly increased the dissolved organic carbon content of soil, their input significantly increased rather than decreased the sorption of PAHs onto soils, with K_d increased by 10∼35%. The FT-ICR-MS and other spectral results revealed that the small phenolic structure-containing molecules (e.g., polyphenols, lignin, and tannin) in BBS-DOMs were preferentially bound to soil. These preferentially binding molecules enhanced the interaction between PAHs and soils by the additional molecular bridging effect of π-π electron donor-acceptor interaction. These results give crucial evidence to understand the environmental fate and risk of BBS-DOMs and PAHs co-deposition into soils after a wildfire.