UCLA

1,4-Dioxane, a probable human carcinogen, is a heterocyclic ether increasingly found as a contaminant in water supplies. Recent studies have reported that 1,4-dioxane can be biodegraded by a variety of microorganisms, and bioremediation may be an effective strategy for 1,4-dioxane contaminated sites. However, reliable monitoring tools to validate biodegradation of 1,4-dioxane are still lacking. Molecular biological tools and stable isotope-based tools have been previously applied as diagnostic tools for monitored natural attenuation and engineered bioremediation of various organic and inorganic compounds. In this study, molecular biological tools were used for determining bacterial populations, and for associating 1,4-dioxane biodegradation with relative copy numbers of phylogenetic and functional genes. These biomarkers were amplified using primers designed from the genome sequence data of 1,4-dioxane-degrading bacterium Pseudonocardia dioxanivorans CB1190, and were correlated with measured biodegradation rates. The results revealed that abundance of DXMO and 16S rRNA were in agreement with 1,4-dioxane biodegradation rates, and could be used to illustrate the inhibitory effect of co-contaminant transition metals Cu(II), Cd(II), Ni(II), and organic ligands such as tannic acid and L-cysteine. It should be recognized that biomarkers provide an indirect association between genes and enzyme activity. Factors regulating protein synthesis and catalytic activities of enzymes are not captured by nucleic acid-based biomarkers. This complicates the interpretation of biomarkers for predicting biodegradation rates. Compound specific isotope analysis (CSIA) could be used as another diagnostic tool to assess 1,4-dioxane biodegradation. In this study, hydrogen and carbon isotope analyses of 1,4-dioxane were successfully developed to determine isotope signatures of commercial 1,4-dioxane, and applied to determine kinetic isotope fractionation associated with biodegradation in both pure and mixed cultures, as well as abiotic degradation of 1,4-dioxane. During biodegradation, both ²H and ^{13(/super>C were enriched, while abiotic processes could enrich only 2H in residual 1,4-dioxane. This indicated that combined carbon and hydrogen isotope analyses of 1,4-dioxane allow differentiation of biological processes from abiotic mechanisms. Availability of stable isotopic and molecular biological tools will allow environmental engineering professionals to include bioremediation as an effective strategy in the cleanup of specific environmental contaminants.}