Introduction

There is considerable interest in the application of biological systems to remediate polycyclic aromatic hydrocarbon (PAH) contamination in the environment (Chen et al., 1999). Recent research on the bioremediation of environmentally relevant chemicals has centred on four important aspects: first, the characterization of the biodegradation processes useful for the treatment of xenobiotic compounds in soil; second, the development of technical protocols for increasing the degradation rates and substrate ranges of enzymes from microorganisms; third, the design and engineering of bioreactor systems and biotreatment strategies to optimize biodegrada-tion processes; and fourth, development of information on the ecological and human health risks associated with exposure to the chemicals (Mueller, Cerniglia & Pritchard, 1996).

Low-molecular-weight PAHs, such as naphthalene, acenaphthene, acenaphthylene, fluorene, anthracene, and phenanthrene (Fig. 7.1), are transformed rapidly by many bacteria and fungi (Pothuluri et al., 1992a,b, 1993; Sutherland et al., 1995; Eriksson, Dalhammar & Borg-Karlson, 2000). High-molecular-weight PAHs, however, are more recalcitrant in the environment and resist both chemical and microbial degradation (Atlas & Cerniglia, 1995; Ahn, Sanseverino & Sayler, 1999; Kanaly & Harayama, 2000).

Benzo[a]pyrene, one of the most recalcitrant PAHs in soil, adsorbs to the soil matrix and thus is physically unavailable to degradative bacteria and fungi (Banks, Lee & Schwab, 1999). The formation of non-extractable bound residues is a significant sink of PAHs in soils (Richnow et al., 2000).