Date Published: October 9, 2012
Author(s): Andrew D Maness, Kimberly S Bowman, Jun Yan, Fred A Rainey, William M Moe.
The contaminant concentrations over which type strains of the species Dehalogenimonas alkenigignens and Dehalogenimonas lykanthroporepellens were able to reductively dechlorinate 1,2-dichloroethane (1,2-DCA), 1,2-dichloropropane (1,2-DCP), and 1,1,2-trichloroethane (1,1,2-TCA) were evaluated. Although initially isolated from an environment with much lower halogenated solvent concentrations, D. alkenigignens IP3-3T was found to reductively dehalogenate chlorinated alkanes at concentrations comparable to D. lykanthroporepellens BL-DC-9T. Both species dechlorinated 1,2-DCA, 1,2-DCP, and 1,1,2-TCA present at initial concentrations at least as high as 8.7, 4.0, and 3.5 mM, respectively. The ability of Dehalogenimonas spp. to carry out anaerobic reductive dechlorination even in the presence of high concentrations of chlorinated aliphatic alkanes has important implications for remediation of contaminated soil and groundwater.
In industry, polychlorinated ethanes and propanes are used as solvents, degreasing agents, and paint removers; they are also globally produced on a massive scale as intermediates during production of other industrially important chemicals ([De Wildeman and Verstraete, 2003]; [Field and Sierra-Alvarez, 2004]). Due to spills and past disposal methods, these chlorinated organic compounds are prevalent groundwater and soil contaminants. For example, 1,2-dichloroethane (1,2-DCA) is present in at least 570 current or former Superfund sites [(ATSDR 2001]), and 1,2-dichloropropane (1,2-DCP) is present at more than 100 Superfund sites ([Fletcher et al., 2009]). The prevalence of these polychlorinated alkanes as environmental contaminants is of concern because of their known or suspected toxicity and/or carcinogenicity ([ATSDR, 2001]; ).
Experiments were carried out in 25 mL glass serum bottles (Wheaton) sealed with butyl rubber stoppers and aluminum crimp caps. Each serum bottle contained 10 mL titanium-citrate reduced anaerobic basal medium prepared as described by ([Moe et al. 2009]) except that 5 mM acetate was replaced with 0.05 mM each of acetate, pyruvate, and lactate. The 15 mL gas headspace was comprised of H2/N2 (80%/20%, v/v). Replicate serum bottles were spiked with neat, filter sterilized 1,2-DCA (>99.8% purity, Sigma Aldrich, St. Louis, MO), 1,2-DCP (99%, Sigma Aldrich, St. Louis, MO), or 1,1,2-TCA (96%, Sigma Aldrich, St. Louis, MO) to achieve target initial aqueous phase concentrations ranging from 0.5 to 15 mM after dissolution and equilibration.
The quantity of the dechlorination product determined at the end of the eight week incubation period as a function of initial aqueous-phase 1,2-DCA, 1,-DCP, and 1,1,2-TCA is shown in Figures 1, 2 and 3 respectively.
As a basis for comparing the concentrations tested here relative to saturation concentrations, solubility in water at 20°C is 86.1 mM for 1,2-DCA ([Horvath et al., 1999]), 23.9 mM for 1,2-DCP ([Horvath et al., 1999]), and 32.9 mM for 1,1,2-TCA (ATSDR ). Also as a basis for comparison, groundwater in the well from which D. lykanthroporepellens BL-DC-9T was isolated had 1,2-DCA, 1,2-DCP, and 1,1,2-TCA concentrations that averaged 5.5 mM, 0.6 mM, and 2.8 mM, respectively ([Bowman et al., 2006]; [Yan et al., 2009a]). Results determined here indicate that both D. alkenigignens IP3-3T and D. lykanthroporepellens BL-DC-9T can reductively dehalogenate 1,2-DCA, 1,2-DCP, and 1,1,2-TCA at concentrations comparable to those present in the DNAPL source zone area of the Brooklawn area of the PPI site.
1,2-DCA: 1,2-dichloroethane; 1,2-DCP: 1,2-dichloropropane; 1,1,2-TCA: 1,1,2-trichloroethane.
The authors declare that they have no competing interests.
JY conducted preliminary experiments to assess the range of chlorinated solvents dehalogenated by D. lykanthroporepellens BL-DC-9T. ADM and KSB carried out the final experiments with D. alkenigignens IP3-3T and D. lykanthroporepellens BL-DC-9T. WMM and FAR guided the research. All authors contributed to data interpretation and writing of the manuscript. All authors read and approved the final manuscript.