Sequestration and biodegradation of polycyclic aromatic hydrocarbon contamination in soils

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous by-products of combustion. They are found in high concentrations in the soils of former wood preservative sites and former municipal gasworks. Many PAHs are toxic and carcinogenic. The primary mechanism for PAH removal from soils is biodegradation. PAH biodegradation in soil is the focus of this dissertation.; The first experimental chapter of the dissertation investigated the fate of radiolabeled pyrene and chrysene added to soils and sands with and without inoculation with soil containing degradative microorganisms. Rate and extent of mineralization varied with compound and matrix type. Mineralization never accounted for more than 35% of PAH fate. The amount of added compound extractable from the matrix decreased consistently in live samples regardless of matrix. The fraction of added label recovered by combusting the soil after extraction increased in samples with active microorganisms regardless of matrix, although more sandy soils had a more rapid increase in the formation of unextracted residual. Extractable and residual fractions remained relatively constant in samples inhibited with sodium azide.; The second experimental chapter reports on the effect of varying redox conditions on PAH contamination that aged in the soil for more than 75 years. Under aerobic conditions, less than half of the aged PAH contamination was degraded in nine month incubation. When nitrate and sulfate were added as electron acceptors, more than two-thirds of the contamination (up to a maximum of 82%) was degraded. When hydrogen filled the headspace of the incubation bottles, similar disappearance of PAHs was observed.; The third experimental chapter investigated one possible mechanism for the incorporation of PAH metabolites into soil organic matter. The pyrene metabolite 1-hydroxypyrene was found to be reactive with laccase, an enzyme thought to be involved in the formation of natural organic matter. While pyrene quinones are a major reaction product, several coupled compounds are also formed. This mechanism may be one explanation for the formation of unextractable residues in soil.; The final section summarizes the conclusions from the experimental chapters. It then places the work as a whole in its scientific and policy context and provides a discussion of future research.