Effect of added heavy metal ions on biotransformation and biodegradation of 2-chlorophenol and 3-chlorobenzoate in anaerobic bacterial consortia.

The effect of added Cd(II), Cu(II), Cr(VI), or Hg(II) at 0.01 to 100 ppm on metabolism in anaerobic bacterial consortia which degrade 2-chlorophenol (2CP), 3-chlorobenzoate (3CB), phenol, and benzoate was examined. Three effects were observed, including extended acclimation periods (0.1 to 2.0 ppm), reduced dechlorination or biodegradation rates (0.1 to 2.0 ppm), and failure to dechlorinate or biodegrade the target compound (0.5 to 5.0 ppm). 3CB biodegradation was most sensitive to Cd(II) and Cr(VI). Biodegradation of benzoate and phenol was most sensitive to Cu(II) and Hg(II), respectively. Adding Cr(VI) at 0.01 ppm increased biodegradation rates of phenol (177%) and benzoate (169%), while Cd(II) and Cu(II) at 0.01 ppm enhanced biodegradation rates of benzoate (185%) and 2CP (168%), respectively. Interestingly, with Hg(II) at 1.0 to 2.0 ppm, 2CP and 3CB were biodegraded 133 to 154% faster than controls after an extended acclimation period, suggesting adaptation to Hg(II). Metal ions were added at inhibitory, but sublethal, concentrations to investigate effects on metabolic intermediates and end products. Phenol accumulated to concentrations higher than those in controls only in the 2CP consortium with added Cu(II) at 1.2 ppm but was subsequently degraded. There was no effect on benzoate, and little effect on acetate intermediates was observed. In most cases, methane yields were reduced by 23 to 97%. Thus, dehalogenation, aromatic degradation, and methanogenesis in these anaerobic consortia showed differential sensitivities to the heavy metal ions added. These data indicate that the presence of heavy metals can affect the outcome of anaerobic bioremediation of aromatic pollutants. In addition, a potential exists to use combinations of anaerobic bacterial species to bioremediate sites contaminated with both heavy metals and aromatic pollutants.