Biotic and Abiotic Anaerobic Transformations of Trichloroethene and cis-1,2-Dichloroethene in Fractured Sandstone

Abstract

A fractured sandstone aquifer at an industrial site in southern California is contaminated with trichloroethene (TCE) and cis-1,2-dichloroethene (cis-DCE) to depths in excess of 244 m. Field monitoring data suggest that TCE is undergoing reduction to cis-DCE and that additional attenuation is occurring. However, vinyl chloride (VC) and ethene have not been detected in significant amounts, so that if transformation is occurring, a process other than reductive dechlorination must be responsible. The objective of this study was to evaluate the occurrence of biotic and abiotic transformation processes at this site for TCE, cis-DCE, and VC. Anaerobic microcosms were constructed with site groundwater and sandstone core samples. 14C-labeled compounds were used to detect transformation products (e.g., CO2 and soluble products) that are not readily identifiable by headspace analysis. The microcosms confirmed the occurrence of biotic reduction of TCE to cis-DCE, driven by electron donor in the groundwater and/or sandstone. VC and ethene were not detected. Following incubation periods up to 22 months, the distribution of 14C indicated statistically significant transformation of [14C]TCE and [14C]cis-DCE in live microcosms, to as high as 10% 14CO2 from TCE and 20% 14CO2 from cis-DCE. In autoclaved microcosms, significant transformation of [14C]TCE and [14C]cis-DCE also occurred; although some 14CO2 accumulated, the predominant 14C product was soluble and could not be stripped by N2 from an acidic solution (referred to as nonstrippable residue, or NSR). Characterization of the NSR by high-performance liquid and ion chromatography identified glycolate, acetate, and formate as significant components. These results suggest that a combination of abiotic and biotic transformation processes is responsible for attenuation of TCE and cis-DCE in the fractured sandstone aquifer. Tracking the distribution of 14C during the microcosm study was essential for observing these phenomena.

Impact of iron sulfide transformation on trichloroethylene degradation

“…Their roles have been demonstrated in several earlier studies of natural geochemical conditions (Davis et al, 2003;Lookman et al, 2005;Darlington et al, 2008). These studies also show that in addition to TCE, FeS is reactive toward a range of organic contaminants that are commonly observed in groundwater at hazardous waste sites.…”

“…Among these, iron sulfide minerals have been shown to be the most potent minerals for abiotic dechlorination (Elsner et al, 2004a,b;Hanoch et al, 2006). Previous studies have demonstrated that iron sulfides make important contributions to the degradation of chlorinated solvents in natural systems (Devlin and Mü ller, 1999;Davis et al, 2003;Kenneke and Weber, 2003;Lookman et al, 2005;Darlington et al, 2008) as well as engineered systems (Kennedy et al, 2006a,b). These studies demonstrated the potential and important roles that iron sulfides could play in the degradation and natural attenuation of groundwater contaminants.…”

“…Abiotic transformation of carbon tetrachloride (CT), trichloroethane (TCA), trichloroethylene (TCE), and tetrachloroethylene (PCE) by iron sulfides has been investigated using pyrite, troilite, and mackinawite Hayes, 1999, 2001;Lee and Batchelor, 2002;Gander et al, 2002;Hansson et al, 2008;Pham et al, 2008;Choi et al, 2009). There are also a few field related studies providing evidence that iron sulfides and abiotic degradation have important contributions to the degradation of chlorinated solvents in natural and engineered systems (Devlin and Mü ller, 1999;Davis et al, 2003;Kenneke and Weber, 2003;Lookman et al, 2005;Kennedy et al, 2006a,b;Shen and Wilson, 2007;Darlington et al, 2008).…”

Identification of chlorinated solvents degradation zones in clay till by high resolution chemical, microbial and compound specific isotope analysis

“…1a. resulting in high enrichment of δ 13 C in cis-DCE. Combined biotic and abiotic transformation of TCE and cis-DCE was also found to proceed in an anaerobic microcosm experiment with sandstone (Darlington et al, 2008). Liang et al (2007) reported strong carbon isotope fractionation during abiotic degradation of PCE (enrichment factor of −30.2‰) and TCE (enrichment factor of −33.4‰) by FeS.…”

“…Dhc containing the gene tceA have been found to respire TCE and cis-DCE (Seshadri et al, 2005) whereas Dhc with the genes vcrA or bvcA respire cis-DCE and vinyl chloride (VC) (Muller et al, 2004;Sung et al, 2006). Several recent laboratory studies have also suggested that abiotic degradation pathways for chlorinated ethenes are of importance in the presence of iron minerals (Darlington et al, 2008;Ferrey et al, 2004;He et al, 2008He et al, , 2010Jeong et al, 2011;Lollar et al, 2010). Biotic and abiotic degradations of chlorinated ethenes and ethanes have been documented by compound specific isotope analysis (CSIA) in several studies (for chlorinated ethenes e.g.…”