Assessment of factors governing biodegradability of PAHs in three soils aged under field conditions

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous contaminants of great environmental concern due to their toxic, mutagenic and carcinogenic properties. This study correlates soil characteristics (i.e. soil organic matter particle- and pore-size distribution) with extractability and toxicity data (LUMIStox, Ostracod) to investigate factors that govern biodegradability of PAHs in three historically contaminated soils. Desorption of PAHs occurred most readily from soil TA1 (82%), followed by soil AS3.7 (69%) and soil WG2 (20%). This is in line with toxicity data, as the soil in which the greatest contaminant desorption (SFE) was observed exhibited the highest toxicity (TA1). Of the three soils, pronounced biodegradation of 2-4-ring, and slight biodegradation of 5-ring PAHs was observed only in AS3.7, while no decrease of PAHs was reported for soils WG2 and TA1 during the degradation experiment. Strong sorption reduced pollutant bioavailability in WG2 and hence hampered biodegradation. By contrast, pollutant sorption was weak in TA1 and microbial activity was most likely inhibited due to high toxicity in this soil. Based on our results we conclude that biodegradation of PAHs in soils is determined by a number of phenomena with complex interactions between them. Consideration of a single factor will be misleading and may result in false prediction of the biodegradation potential.