Mineralization of sparsely water soluble polycyclic aromatic hydrocarbons in a water table fluctuation zone

The mineralization potential of sparsely water-soluble polycyclic aromatic hydrocarbons (PAHs) within a highly diesel-contaminated watertable fluctuat ion zone (WTFZ) was investigated using core-scale column microcosms. Experi mental conditions mimicked overall seasonal changes in water and oxygen con tent at the site. During the first aerobic winter, PAH mineralization rates in the freshly contaminated soil were fastest for contaminant [C-14]- naph thalene which was the least hydrophobic and most water-soluble. Lowering th e water table nearly doubled the mineralization rates of all [C-14]PAHs stu died. During the oxygen-poor summer, all mineralization rates were insignif icant and failed to respond to water table changes. Neither a return to wat er-saturated aerobic (winter) conditions nor lowering the water table under aerobic conditions induced detectable mineralization of [C-14]naphthalene, but lowering the water table did markedly hasten the still slow mineraliza tion of [C-14]phenanthrene and [C-14]anthracene. The time-dependent mineral ization behavior and its response to water table fluctuations were explicab le in terms of microbial responses to the changing oxygen content and deple ting mineral nutrients.