Kinetics of the Transformation of Trichloroethylene and Tetrachloroethylene by Iron Sulfide

Abstract

The transformation of trichloroethylene (TCE), tetrachloroethylene (PCE), and 1,1-dichloroethylene (1,1-DCE) by 10 g/L (0.5 m2/L) FeS in aqueous solution at pH 8.3 was studied in batch experiments. TCE and PCE were transformed by FeS with pseudo-first-order rate constants, corrected for partitioning to the sample headspace, of (1.49 ± 0.14) × 10-3 h-1 (TCE) and (5.7 ± 1.0) × 10-4 h-1 (PCE). A 17% decrease in the concentration of 1,1-DCE was observed over 120 days; however, no reaction products were detected. TCE and PCE transformation data were fit to a rate law assuming transformation of TCE via parallel reaction pathways to acetylene and cis-1,2-dichloroethylene (cis-DCE) and transformation of PCE via parallel reaction pathways to acetylene and TCE. Acetylene was the major reaction product for both TCE and PCE. Determination of rate constants for each reaction pathway indicated that TCE was transformed to acetylene 11.8 ± 1.1 times faster than to cis-DCE and that PCE was transformed to acetylene 8.2 ± 1.8 times faster than to TCE. Additional minor reaction products were vinyl chloride (VC) for TCE and cis-DCE for PCE. Detection of acetylene as the major product of both TCE and PCE transformation by FeS contrasts with the sequential hydrogenolysis products typically observed in the microbial transformation of these compounds, making acetylene a potential indicator of abiotic transformation of TCE and PCE by FeS in natural systems.

Identification of abiotic and biotic reductive dechlorination in a chlorinated ethene plume after thermal source remediation by means of isotopic and molecular biology tools

“…Although acetylene was not detected in the aquifer, the additional occurrence of abiotic reductive dechlorination cannot be overlooked as acetylene can be further transformed to readily biodegradable compounds such as acetaldehyde, acetate and ethanol in groundwater (Liang et al, 2009). Finally, while biotically produced mackinawite may catalyze abiotic reductive dechlorination of PCE and TCE (Butler and Hayes, 1999), it was shown that cDCE was not reactive with mackinawite (Jeong et al, 2011). Abiotic reductive cDCE dechlorination is thus not likely to take place in the presence of mackinawite, though biotically produced nonmeasurable surface-bound Fe(II) (Han et al, 2012) and other reduced iron minerals such as green rust (Lee and Batchelor, 2002b) may induce such a reaction.…”

Field-scale demonstration of induced biogeochemical reductive dechlorination at Dover Air Force Base, Dover, Delaware

“…From laboratory studies with pure minerals, acetylene is the primary end product of CAH dechlorination (Butler and Hayes, 1998, 1999Gander et al, 2002;Lee and Batchelor, 2002). However, acetylene may not be useful as an indicator of abiotic dechlorination in live systems as it is labile and certainly transient.…”

“…FeS minerals are strongly reduced and facilitate the autoreduction of CAH compounds similar to exposure to elemental iron. Synthetic FeS has been documented to dechlorinate a wide range of chlorinated compounds including PCE, TCE, PCA, CT, PCA, and others (Butler and Hayes, 1998, 1999Gander et al, 2002). Lee and Batchelor (2002) also found good dechlorination rates for PCE, cDCE, and VC by reaction with pyrite (FeS 2 ).…”

Multiple Lines Of Evidence Supporting Natural Attenuation: Lines Of Inquiry Supporting Monitored Natural Attenuation And Enhanced Attenuatin Of Chlorinated Solvents

“…Although the exact pathway has not been fully determined, it is thought that the pathway for TCE oxidation is via the cis-dichlorovinyl radical directly to acetylene (Butler and Hayes, 1999). Because acetylene is unstable and very transient, it is hard to detect.…”