Sorption of 2,4,6-trichlorophenol by Bacillus subtilis

The mobility of 2,4,6-trichloraphenol (TCP) in groundwater may be controlled, in part, by its sorption onto bacterial surfaces. In this study, we perform batch experiments as a function of pH, time, and solid-to-solution ratio to investigate the sorption of TCP by the common soil bacterium Bacillus subtilis. We first describe the experimental data with a hydrophobic partitioning model, in which sorption is controlled by the speciation of the TCP a nd the concentration of bacteria present. This model provides an adequate description of the data below pH 8 but overpredicts sorption in more basic solutions, where negligible sorption is observed for all solid-to-solution ratios. TCP-B. subtilis sorption is better described by a surface complexation model in which both the negative and the neutral forms of TCP form 1:1 surface complexes with the neutral hydroxyl functional groups of the bacteria: R-OH0 + TCP- <-> R-OH-TCP- (log K = 3.01 +/- 0.50) and R-OH0 + HTCP0 <-> R-OH-HTCP0 (log K = 3.77 +/- 0.50). These stability constants may be incorporated into thermodynamic models to predict the fate of TCP in complex systems.