ORIGINAL PAPER Bench-scale biodegradation tests to assess natural attenuation potential of 1,4-dioxane at three sites in California Mengyan Li • E. Tess Van Orden • David J. DeVries • Zhong Xiong • Rob Hinchee • Pedro J. Alvarez Received: 16 August 2014 / Accepted: 10 September 2014 / Published online: 30 September 2014 Ó Springer Science+Business Media Dordrecht 2014 Abstract 1,4-Dioxane (dioxane) is relatively recal- citrant to biodegradation, and its physicochemical properties preclude effective removal from contami- nated groundwater by volatilization or adsorption. Through this microcosm study, we assessed the biodegradation potential of dioxane for three sites in California. Groundwater and sediment samples were collected at various locations at each site, including the presumed source zone, middle and leading edge of the plume. A total of 16 monitoring wells were sampled to prepare the microcosms. Biodegradation of dioxane was observed in 12 of 16 microcosms mimicking natural attenuation within 28 weeks. Rates varied from as high as 3,449 ± 459 lg/L/week in source-zone microcosms to a low of 0.3 ± 0.1 lg/L/ week in microcosms with trace level of dioxane ( \ 10 lg/L as initial concentration). The microcosms were spiked with 14 C-labeled dioxane to assess the fate of dioxane. Biological oxidizer-liquid scintillation analysis of bound residue infers that 14 C-dioxane was assimilated into cell material only in microcosms exhibiting significant dioxane biodegradation. Miner- alization was also observed per 14 CO 2 recovery (up to 44 % of the amount degraded in 28 weeks of incuba- tion). Degradation and mineralization activity signif- icantly decreased with increasing distance from the contaminant source area (p \ 0.05), possibly due to less acclimation. Furthermore, both respiked and repeated microcosms prepared with source-zone sam- ples from Site 1 confirmed relatively rapid dioxane degradation (i.e., 100 % removal by 20 weeks). These results show that indigenous microorganisms capable of degrading dioxane are present at these three sites, and suggest that monitored natural attenuation should be considered as a remedial response. Keywords 1,4-Dioxane Á Natural attenuation Á Bioremediation Á Mineralization Á Microcosms Introduction 1,4-Dioxane (dioxane) is a groundwater contaminant of emerging concern due to its potential carcinoge- nicity (IARC 1999) and its recently discovered widespread occurrence at thousands of sites impacted by chlorinated solvent releases in the US and abroad (Mohr et al. 2010). Dioxane was historically used as a stabilizer for industrial solvents, typically 1,1,1- trichloroethane (1,1,1-TCA), thus explaining this M. Li Á E. T. Van Orden Á P. J. Alvarez (&) Department of Civil and Environmental Engineering, Rice University, Houston, TX, USA e-mail: alvarez@rice.edu D. J. DeVries Á Z. Xiong AMEC Environment and Infrastructure, Inc., Irvine, CA, USA R. Hinchee Integrated Science & Technology, Inc., Panacea, FL, USA 123 Biodegradation (2015) 26:39–50 DOI 10.1007/s10532-014-9714-1