The Effect of Temperature on Polycyclic Aromatic Hydrocarbon Persistence in an Unacclimated Agricultural Soil

A laboratory study was conducted to investigate the effect of temperature on the persistence of polycyclic aromatic hydrocarbons (PAHs) incubated in an unacclimated agricultural sandy loam soil. Soil microcosms were spiked with 16 priority pollutant PAHs and placed in incubation chambers at 10, 20, and 30°C. Triplicate sets of microcosms at each temperature were periodically removed from incubation over the 240 day study period and solvent extracted. Concentrations of PAHs in the soil were determined by HPLC analysis of the extracts. Substantial loss of three-ring compounds was observed at all temperatures whereas there was very little apparent loss of five and six-ring compounds at any temperature. The estimated half lives of acenaphthene, fluorene, and phenanthrene were comparable to values reported in the literature, but all other PAHs were more recalcitrant than reported in the literature. Increasing the soil temperature significantly improved the rate and extent of apparent loss of low molecular weight PAHs but had little effect on loss of five and six-ring PAHs. The effect of temperature on first order rate coefficients for loss of fluorene and on zero order rate coefficients for loss of anthracene, fluoranthene, pyrene and benz[a]anthracene was characterized by the Arrhenius equation but for the remaining compounds the Arrhenius equation was not useful. For land treatment of hazardous wastes containing PAHs, measures should be investigated to ensure loss of the more recalcitrant PAHs during the active treatment period and management options should be developed to ensure continued loss of PAHs during closure of a land treatment site when waste applications have ceased