Occurrence, sources and potential risks of polycyclic aromatic hydrocarbons in a permafrost soil core, northeast China

Polycyclic aromatic hydrocarbons (PAHs) in an AMS 14C-dated permafrost soil core extracted from continuous permafrost zone were measured to reconstruct the pollution history from the early Holocene (ca. 15480 a BP) and its potential risks under climate changes were evaluated in northeast China. Total PAH concentrations varied from 209 to 2161 ng/g through the core, which were moderately contaminated in the surface but heavily contaminated historically. Factor analysis indicated that volcanic activity, diagenesis from biological precursors and palaeo forest fires were dominant PAH sources, while petroleum emission was identified in the active layer due to the construction of China–Russia oil pipeline. Significant increases in 5-ring, 6-ring and 7 carcinogenic PAHs (p < 0.05) were observed from surface to the interface of the active layer and ice-rich permafrost layer, showing a selective downward migration in the active layer which might be effected by the repetitive cycles of freezing and thawing. Results implied that PAHs in the ice-rich permafrost layer could lead to an unpredictably serious consequence under the further climate warming.