Arsenic Effects on the Bacterial Degradation of Pentachlorophenol

At wood-preservation facilities, soil and groundwater can become contaminated with pentachlorophenol (PCP) and chromated-copper-arsenate (CCA). While a PCP-degrading Flavobacterium sp. has been identified, PCP degradation can be inhibited by CCA. Results are presented from a study on the effects of arsenic on the growth and metabolic activity of a PCP-degrading Flavobacterium. In all assays, arsenic pentoxide was used as the toxicant. After bacterial inoculation, As was added at levels corresponding to the 96-h EC sub(25), EC sub(50), and EC sub(75) values, and dose response curves were constructed every 24 h. A total of 15 As concentrations were tested, yielding 15 separate bacterial-growth curves. Results indicated that As completely inhibited bacterial growth at concentrations greater than or equal to 600 mu g/ml. At lower levels, no pronounced effect on the lag phase of growth was observed, but growth rate was inhibited during the early logarithmic phase. While As concentrations below 142 mu g/ml did not dramatically inhibit PCP degradation rates, they did elicit an increase in the lag time observed prior to measurable PCP degradation.