Toxicity of chloroform biotransformation to methanogenic bacteria

Batch serum bottle assays were conducted to determine the effect of exposure to and biotransformation of chloroform (CF) on unacclimated, aceticlastic, methanogenic bacteria. Methanogenesis was negatively impacted both during and following exposure of methanogens to CF: methanogenesis was strongly inhibited in the presence of detectable levels of chloroform and maximum methane production (MMP) rates decreased following CF exposure. Using a general nonlinear model it was found that the loss of methanogenic activity was most strongly correlated with the mass of chloroform transformed (nmol CF; r(2) = 0.84), rather than with the time-integrated CF exposure which methanogens received (mu M CF-h; r(2) = 0.60). Comparison of individual data sets supported this finding. Control studies showed that desorption of CF and exposure of methanogens to DCM or possible nonvolatile CF metabolites did not cause decreased MMP rates. Based on these results, it is concluded that CF biotransformation is toxic to unacclimated, aceticlastic methanogenic bacteria and nonlinear with respect to the mass of CF transformed.