Introduction

Fossil energy reserves are valuable natural resources that underpin most major world economies. The extraction, transport and utilization of these resources inevitably leads to the release of these substances to environmental compartments where they are deemed undesirable. For instance, petroleum or petroleum distillation products often occur as contaminants in soils, aquifers and surface waters via a myriad of mechanisms including leaking underground storage tanks, aboveground spills and release by marine transport vessels. Since environmental matrices (air, water and soil) are completely integrated, all are susceptible to a reduction in quality and often quantity due to the release of pollutant materials. When this occurs, a great deal of concern is associated with the impact of the hydrocarbons on humans and recipient environments. However, this impact cannot be correctly gauged without information on the transport and fate characteristics of the individual contaminants.

A major factor governing the transport and fate of contaminant hydrocarbons is their susceptibility to metabolism by aerobic and anaerobic microorganisms. While a plethora of information is available on the prospects for aerobic biodegradation, comparatively little is understood about anaerobic hydrocarbon biotransformation. However, it is well recognized that anaerobic microbial activities directly or indirectly impact all major environmental compartments. In many environments, most notably the terrestrial subsurface, oxygen concentrations are often initially low. With rapid utilization by hydrocarbonoclastic microorganisms and limited rates of reoxygenation, oxygen becomes depleted. Without the reactive power of molecular oxygen, the biodegradation rate of hydrocarbons slows down and contamination problems are exacerbated. Nevertheless, some of the most toxicologically important components of petroleum can be metabolized, even in the absence of oxygen.