METHANOTROPHIC CHLOROETHENE TRANSFORMATION CAPACITIES AND 1,1-DICHLOROETHENE TRANSFORMATION PRODUCT TOXICITY

For a mixed methanotrophic culture grown under copper deficiency, the relative transformation capacities of the chloroethenes with 10 mM formate present was in the order from highest to lowest: 1,2-trans-dichloroethylene (t-DCE); 1,2-cis-dichloroethylene (c-DCE); vinyl chloride (VC); trichloroethylene (TCE); and 1,1-dichloroethylene (1,1-DCE). Respective values were 4.8, 3.6, 2.3, 0.85, and 0.13 mu mol transformed per mg of cells. Chloroethenes with asymmetric chlorine distributions had lower transformation capacities, probably due to higher transformation product toxicity. While 1,1-DCE itself was not toxic at the concentrations evaluated (up to 1 mg/L), its transformation products were highly toxic. Aquifer microcosms transformed up to 4.8 mg/L VC with no apparent toxic effects, but when both VC and 1,1-DCE were present, about 75% less transformation of VC and a marked decrease in methane oxidation rate resulted because of 1,1-DCE transformation product toxicity. About 25 times more VC was transformed in the soil microcosms per unit of methane consumed than in aqueous batch tests.