Desorption and mineralization kinetics of phenanthrene and chrysene in contaminated soils

The relative rates of desorption and mineralization for spiked concentrations of [C-14]phenanthrene and [C-14]chrysene preloaded on two previously contaminated soils (f(oc), 0.029 and 0.0026) were investigated using static, slurry phase microcosms (V-water/V-soil = 10) Desorption rates of [C-14]phenanthrene and [C-14]chrysene preloaded on the contaminated soils were much faster than observed mineralization rates, whereas the desorption rates of native polynuclear aromatic hydrocarbons (PAH) in the higher organic content contaminated soil were equal to or slower than mineralization rates. This suggests that the desorption of aged PAH may control their degradation and may explain the persistence of PAH even in soils containing a large and active community of PAH-degrading microorganisms. In addition, using C-14-spiked PAH in contaminated soils to measure desorption and biodegradation rates may lead to misleading interpretations of the environmental fate of soil-bound polynuclear aromatic hydrocarbons.