Mineralization of Sparsely Water-Soluble Polycyclic Aromatic Hydrocarbons in a Water Table Fluctuation Zone

Abstract

The mineralization potential of sparsely water-soluble polycyclic aromatic hydrocarbons (PAHs) within a highly diesel-contaminated water table fluctuation zone (WTFZ) was investigated using core-scale column microcosms. Experimental conditions mimicked overall seasonal changes in water and oxygen content at the site. During the first aerobic winter, PAH mineralization rates in the freshly contaminated soil were fastest for contaminant [14C]naphthalene which was the least hydrophobic and most water-soluble. Lowering the water table nearly doubled the mineralization rates of all [14C]PAHs studied. During the oxygen-poor summer, all mineralization rates were insignificant and failed to respond to water table changes. Neither a return to water-saturated aerobic (winter) conditions nor lowering the water table under aerobic conditions induced detectable mineralization of [14C]naphthalene, but lowering the water table did markedly hasten the still slow mineralization of [14C]phenanthrene and [14C]anthracene. The time-dependent mineralization behavior and its response to water table fluctuations were explicable in terms of microbial responses to the changing oxygen content and depleting mineral nutrients.