Sources and fate of polycyclic aromatic compounds (PAHs, oxygenated PAHs and azaarenes) in forest soil profiles opposite of an aluminium plant

Little is known about oxygenated polycyclic aromatic hydrocarbons (OPAHs) and azaarenes (AZAs) in forest soils. We sampled all horizons of forest soils from five locations at increasing distances from an Al plant in Slovakia, and determined their polycyclic aromatic compound (PACs) concentrations. The Sigma 29PAHs concentrations were highest in the Oa and lowest in the Oi horizon, while the Sigma 14OPAHs and Sigma 4AZAs concentrations did not show a consistent vertical distribution among the organic horizons. The concentration ratios of PAHs and OPAHs between deeper O horizons and their overlying horizon (enrichment factors) were positively correlated with the octanol-water partition coefficients (K-OW) at several locations. This is attributed to the slower degradation of the more hydrophobic PACs during organic matter decomposition. PACs concentrations decreased from the organic layer to the mineral horizons. The concentrations of Sigma 29PAHs (2400-17,000 ng g(-1)), Sigma 14OPAHs (430-2900 ng g(-1)) and Sigma 4AZAs (27-280 ng g(-1)) in the mineral A horizon generally decreased with increasing distance from the Al plant. In the A horizons, the concentrations of Sigma 29PAHs were correlated with those of Sigma 14OPAHs (r = 0.95, p = 0.02) and Sigma 4AZAs (r = 0.93, p = 0.02) suggesting that bioturbation was the main transport process of PACs from the organic layer into the mineral soil. At each location, the concentrations of PACs generally decreased with increasing depth of the mineral soil. Enrichment factors of PAHs in the mineral horizons were not correlated with KOW, pointing at colloid-assisted transport and bioturbation. The enrichment factors of OPAHs (in mineral horizons) at a site were negatively correlated with their KOW values indicating that these compounds were leached in dissolved form. Compared to a study 13 years before, the concentrations of PAHs had decreased in the O horizons but increased in the A and B horizons because of soil-internal redistribution after emissions had been reduced. (C) 2018 Elsevier B.V. All rights reserved.