1,4-dioxane was commonly used as a stabilizer in 1,1,1-trichloroethane formulations and is now frequently detected at sites where chlorinated solvents are present. A major challenge to 1,4-dioxane remediation concerns chemical characteristics that result in migration and persistence. Given the limitations associated with traditional remediation methods, interest has turned to bioremediation to address 1,4-dioxane contamination. The overall objective of this project was to determine the susceptibility of 1,4-dioxane to biodegradation over a range of redox conditions.
The potential for 1,4-dioxane biodegradation was examined using multiple inocula sources and electron acceptor amendments. The inocula included uncontaminated agricultural soils and river sediments as well as sediments from two 1,4-dioxane contaminated sites. Compound specific isotope analysis (CSIA) was used to investigate biodegradation in a subset of the microcosms. Also, DNA was extracted from microcosms exhibiting 1,4-dioxane biodegradation for microbial community analysis using 16S rRNA gene amplicon and shotgun sequencing.
The iron/ethylenediaminetetraacetic acid/humic acid or sulfate amendments did not result in 1,4-dioxane biodegradation in the majority of cases. However, 1,4-dioxane biodegradation was noted in a subset of the nitrate amended and no electron acceptor treatments (although slow biodegradation rates were observed). In two of the three cases examined, CSIA provided additional evidence for 1,4-dioxane biodegradation. Microbial community analysis indicated unclassified Comamonadaceae and 3 genus incertae sedis were obtaining a growth benefit during anaerobic 1,4-dioxane degradation. Under aerobic conditions, 1,4-dioxane biodegradation was observed with all six inocula. A comparison of live microcosms and live controls (no 1,4-dioxane) indicated seventeen genera were enriched following exposure to 1,4-dioxane, suggesting a growth benefit for 1,4-dioxane degradation. The three most enriched were Mycobacterium, Nocardioides, and Kribbella. The three most common functional genes detected were those aligning to Rhodococcus jostii RHA1 prmA, Rhodococcus sp. RR1 prmA, and Burkholderia cepacia G4 tomA3.
The current study indicates 1,4-dioxane biodegradation under anaerobic (likely methanogenic) conditions is feasible. Therefore, natural attenuation of 1,4-dioxane may occur over a wider range of conditions, notably methanogenic areas where highly reducing conditions exist either naturally or as a result of enhanced reductive dechlorination. The work is novel as it is the first to document the frequency of 1,4-dioxane biodegradation over a range redox conditions and inocula types and provides evidence for the feasibility of anaerobic 1,4-dioxane remediation. Under aerobic conditions, 1,4-dioxane degradation was observed with all inocula types, indicating 1,4-dioxane degraders are widespread. Further, a large number of genera were enriched following 1,4-dioxane degradation. The aerobic study is innovative as it combines taxonomic and functional data to generate a more complete picture of the multiple microorganisms and genes linked to 1,4-dioxane degradation in mixed communities. Additional research is needed to determine the occurrence of the microorganisms putatively linked to anaerobic 1,4-dioxane biodegradation at contaminated sites.