Bioavailability of Aromatic Hydrocarbons and Their Interactions with Natural Organic Matter: Linking Molecular- and Microbial-Scale Interactions

Accurately measuring the bioavailability of organic contaminants associated with complex environmental matrices is necessary for assessing contaminant risk, as well as for evaluating the effectiveness of proposed and in-place remediation strategies. Due to its importance, the bioavailability of organic contaminants associated with soils and sediments has been widely examined at the macroscopic or bulk-scale and found to be highly controlled by natural organic matter (NOM) as well as the contact time between the contaminant and environmental matrix. Although chemical and physical interactions between natural organic matter and contaminant molecules are expected to influence bioavailability, there has been minimal success identifying how these interactions impact the bioavailability of the contaminants. The aims of this project are to identify the key physical, chemical, and biological conditions and processes governing bioavailability of aromatic hydrocarbons associated with NOM, such as humic and fulvic acids and humin (1). Molecular interactions and dynamics of aromatic hydrocarbon molecules associated with NOM are being characterized and quantified using liquid- (2) and solid-state (3) deuterium nuclear magnetic resonance experiments, fluorescence probe experiments (4), and NOM surface area and adsorption capacity characterization. To assess bioavailability, we are measuring the activity of the degradative enzyme naphthalene 1,2- dioxygenase (NDO) (5) as it catalyzes the degradation of aromatic hydrocarbons associated with NOM. NDO activity will be characterized as a function of NOM type and concentration, and NOM-aromatic hydrocarbon aging time. Using the analytical methods noted above to examine NOM-aromatic hydrocarbon samples before and after exposure to the enzyme will permit characterization at a molecular-scale of the effect of NOM-aromatic substrate interactions on enzymatic bioavailability, i.e., molecular interactions will be identified that facilitate or hinder enzymatic bioavailability of aromatic hydrocarbons associated with NOM. Enzymatic-scale bioavailability subsequently will be coupled to the microbial-scale by measuring the bioavailability of aromatic hydrocarbons associated with NOM to reporter microbes that luminesce upon expressing NDO in the presence of aromatic substrates. Describing bioavailability over this continuum of scale, i.e., from molecular to microbial, will provide a basis for extrapolating the environmental consequences of aromatic hydrocarbon contamination from both discrete chemical interactions and microbial-level responses.