The sorption of hydrophobic organic chemicals to bacteria

The toxicity and time-dependent sorption of HOCs to Rhodococcus rhodochrous were investigated. These studies were conducted with three HOCs: pentachlorophenol (PCP), hexachlorobenzene (HCB), and dichlorobiphenyl (DPCB). In experiments, environmentally relevant chemical concentrations were applied to living (both growing and non-growing) as well as to dead R. rhodochrous bacteria.; For PCP at low concentrations, neither bacterial growth nor death was affected by the PCP. At higher concentrations, some of the bacteria died and the percentage of bacteria that died increased with increasing PCP concentrations. In sorption studies at low PCP concentrations and at chemical equilibrium, K_p for living bacteria was almost three times greater than the K_p for dead bacteria. The reason for this is that live bacteria can actively take up PCP (an ionizable chemical) while dead bacteria can not. At higher PCP concentrations, the K_ps for both the dead and living bacteria decreased rapidly and then more slowly as the PCP concentration increased. This is attributed to (a) death of the living bacteria due to PCP toxicity and (b) saturation of site specific sorption for all bacteria.; HCB did not affect the growth or death of the bacteria at all HCB concentrations investigated. In the time-dependent HCB sorption experiments with dead and non-growing bacteria, K_p remained constant with time; with growing bacteria, K_p decreased with time during the first four days, stayed almost constant for about the next 10 to 15 days, and then gradually increased to its initial value over a period of about 40 days. The maximum decrease in K_p depended on the amount of food provided. The initial decrease was primarily due to the rate of bacterial growth being high enough and HCB sorption rate being low enough that chemical equilibrium between the bacteria and the surroundings could not be maintained. After the bacteria stopped growing, sorption continued until chemical equilibrium was reached. Sorption rates were heavily dependent on size and density of the bacterial aggregates; these changed with time.; Results for DPCB (which had a similar K_p to that of HCB) were similar to those for HCB.