Biodegradation rates of low concentrations of 1,4-dioxane in impacted site sediments and agricultural soils and an investigation of the microorganisms and genes involved.

1,4-Dioxane was used as a stabilizer in 1,1,1-trichloroethane formulations and is frequently detected at sites where the chlorinated solvents are present. Major challenges concern chemical characteristics that result in migration and persistence, often resulting in large and dilute plumes. The objectives of this study were to 1) examine the effectiveness of basal salts medium (BSM) and yeast extract for enhancing 1,4-dioxane biodegradation removal rates at low 1,4-dioxane concentrations, 2) identify phylotypes utilizing 1,4-dioxane and/or metabolites to support growth and 3) evaluate the impact of bioaugmentation with agricultural soil microorganisms on 1,4-dioxane removal. 1,4-Dioxane removal rates were examined in laboratory microcosms with sediment from three impacted sites (Sites 1-3) and four agricultural soils (Soils 1-4). 1,4-Dioxane biodegradation was only observed in microcosms inoculated with sediments from one of the three sites (called Site 1). Amending Site 1 microcosms with BSM and yeast extract improved biodegradation rates, suggesting these amendments positively impacted indigenous 1,4-dioxane degraders. In contrast to the impacted sites, 1,4-dioxane was degraded in microcosms inoculated with each of the four agricultural soils. Further, bioaugmentation with agricultural soils resulted in 1,4-dioxane removal in Site 2 microcosms. Phylotypes benefiting from 1,4-dioxane (or metabolite) biodegradation were determined by identifying those significantly enriched in the live sample microcosms (with 1,4-dioxane) compared to the live control microcosms (no 1,4-dioxane) using DESeq2. Notably, the group of enriched phylotypes also included those previously linked to 1,4-dioxane biodegradation (Rhodococcus, Flavobacterium, Arthrobacter, Gemmatimonas and unclassified Rhizobiales and Chitinophagaceae). PICRUSt2 analysis indicated a number of enriched phylotypes were associated with ammonia/particulate methane monooxygenase subunits as well as propane monooxygenase subunits. Overall, the results suggest yeast extract and BSM can be beneficial for promoting 1,4-dioxane biodegradation at sites with indigenous 1,4-dioxane. At other sites, bioaugmentation with agricultural soil microorganisms may represent the basis for a promising remediation strategy.