Biodegradation of 1,4-Dioxane under Anaerobic Conditions

Used mainly as a solvent stabilizer, 1,4-dioxane is present at numerous hazardous waste sites impacted with chlorinated solvents and is also present in consumer products such as shampoos, cosmetics and detergents. 1,4-dioxane is a concern because of its health effects; it is listed as a probable human carcinogen and emerging contaminant by EPA. Bioremediation is an alternative approach to cleaning up contaminated sites but 1,4-dioxane is generally recalcitrant to biodegradation under anaerobic conditions. However, observations from two contaminated sites indicate that biodegradation is occurring; a microcosm study was performed to evaluate this hypothesis.

The first set of microcosms (Set I) was prepared using soil and groundwater from both sites. [U¹⁴C]1,4-dioxane was added to assess the extent of biodegradation. 1,4-dioxane, volatile organic compounds, isopropyl alcohol, acetone and acetate were monitored over time. A new set of microcosms (Set II) was prepared for Site 1 in which dissolved iron has been monitored closely over time.

Based on ¹⁴C distribution, ~21% of 1,4-dioxane was converted into other soluble compounds, which are  presumptively acetate and to a lesser extent formate (both non-hazardous), in microcosms amended with Fe(III)-EDTA from Site 1. Similarly, degradation activity and iron reduction have been observed for the Set II microcosms with the same amendment.

These results support the hypothesis of in situ anaerobic biodegradation of 1,4-dioxane. Additional experiments will be performed to evaluate what limits the rate and extent of biodegradation, the role of other contaminants, and how this process can be enhanced.