Bioformation of polycyclic aromatic hydrocarbons in soil under oxygen deficient conditions

Possible formation of polycyclic aromatic hydrocarbons (PAHs) through biological processes in soil was investigated. Soil, plant material, and a mixture of both were waterlogged and incubated for 2 years, resulting in long lasting oxygen deficient conditions. Sample extracts were analysed by HPLC for 15 PAHs. In soil with or without added plant material, the contents of 4-, 5-, and 6-ring PAHs increased significantly to 139–238% of the contents before incubation. Concentrations decreased for several 3-ring PAHs, probably due to anaerobic biodegradation. When only plant material was incubated, the increase was significant for the 4-ring PAHs benzo[a]anthracene and chrysene and all 5- and 6-ring PAHs (250–674%). It was assumed that PAHs are formed from aromatic compounds of plant material and humus precursors. Under oxygen deficient conditions this may lead to natural background levels of PAHs in soils.