Biodegradation of 1,4-dioxane in planted and unplanted soil: effect of bioaugmentation with amycolata sp. CB1190

1,4-dioxane is one of the most recalcitrant and toxic contaminants in the subsurface. This study investigated the potential to enhance dioxane biodegradation in both planted and unplanted soil, by adding the dioxane-degrading actinomycete, Amycolata sp. CB1190. Dioxane was not removed within 120 days in sterile controls or in viable microcosms not amended with CB1190. Poplar root extract (40 mg/L as COD) stimulated dioxane degradation in bioaugmented soil, and 100 mg/L dioxane were removed within 45 days. Other co-substrates that enhanced dioxane degradation by CB1190 include tetrahydrofuran (THF) and 1-butanol, while glucose and soil extract did not affect dioxane degradation. The stimulatory effect of THF was partly due to enhanced enzyme induction, while that of root extract and 1-butanol was attributed to additional growth of CB1190. In another experiment with dioxane added at 10 mg/kg-soil, reactors planted with hybrid poplar trees removed (by evapotranspiration and biodegradation in the root zone) more dioxane within 26 days than unplanted reactors, regardless of whether CB1190 was added. Nevertheless, CB1190 enhanced mineralization of [14C]-dioxane in all experiments. This enhancement was more pronounced in unplanted soil because plant uptake reduced the availability of dioxane for microbial degradation. These results suggest that bioaugmented phytoremediation is an attractive alternative to remove dioxane from shallow contaminated sites.