Effects of pH and ionic strength on the adsorption of Cs, Sr, Eu, Zn, Cd and Hg by Pseudomonas putida

Bacterial metal accumulation may influence the mobility and chemical form (speciation) of metals in the environment. The passive adsorption of six metals (Cs, Sr, Eu, Zn, Cd and Hg) by a soil bacterium, Pseudomonas putida, was studied in the present work using a radiotracer batch-distribution technique. To replicate natural conditions, the adsorption was considered as a function of pH (4-10) and ionic strength (0.01 M and 0.1 M KCl) at a low metal concentration (10(-8) M). P. putida exhibited a total metal accumulating capacity of 200-1000 meq kg(-1) bacteria (dry weight) (measured in 0.01 M KCl at pH 6.4). This capacity is comparable to that of many organic soil components and it is above the capacity of most inorganic constituents. The following affinity order of adsorption was observed: Hg>Eu>Cd,Zn,Sr>Cs. The results indicate that the bacterial surface carries different sites that exhibit varying affinity and capacity for binding metal ions. It can be concluded that the overall adsorption of metals by P. putida is determined by several interacting processes related to the properties of both the metals and the bacterial surface and to the composition of the solution phase (pH as well as ionic strength).