Influence of Compost Addition on the Bioavailability of Polycyclic Aromatic Hydrocarbons in Brownfield Soils

In this study the influence of compost addition on the bioavailability of polycyclic aromatic hydrocarbons (PAHs) was investigated using three soils consisting of a sandy loam spiked with diesel that had been aged for three years, a sandy clay loam and a sandy loam that were collected from brownfield sites contaminated with coal ash and coal tar, respectively. Soils amended with two composts made from contrasting feedstock (green waste and predominantly meat waste) at two different ratios (250 and 750 t/ha) were incubated for six months. The bioavailable content of five target PAHs including naphthalene, phenanthrene, pyrene, benzo[a]pyrene and benzo[ghi]pyrene were quantified by the difference between the total concentration determined by sequential ultrasonic extraction and the unavailable concentration determined by cyclodextrin extraction. Results showed that changes of bioavailability of PAH during composting process differed with soils and composts. In the soils amended with meat compost, a trend of increase followed by decrease of bioavailability was found and the amount of compost at the transition point was larger in clay loam than sandy loam. In the soils incubated with green compost, a more complex pattern was observed and the mechanisms were not yet fully understood.