Impact of Shewanella oneidensis on heavy metals remobilization under reductive conditions in soil of Guilan Province, Iran

Remobilization of heavy metals in contaminated soil due to anaerobic bioreduction by Shewanella oneidensis was studied. Glucose and anthraquinone-2,6-disulphonate (AQDS) were used as an electron donor and an electron shuttle, respectively. The bioreduction caused a gradual increase in dissolved Mn(II) concentration upto 15 days followed by stationary state. The aqueous Fe(II) concentration increased and reached a highest level on the 10 th day, followed by a slight decrease before the steady state was reached. The concentration of Cu(II) was at its extreme level on 5 th day and then decreased before reaching the steady state. The highest dissolution was observed for Zn(II) on the 10 th day followed by a decrease upto 25 th day. Enhanced reduction of Fe(III) and mobilization of selected heavy metals were observed in the presence of S. oneidensis and AQDS. The soluble and acid-extractable Fe(II) concentration was higher in the presence of glucose. The remobilization efficiencies of Mn(II), Fe(II), Cu(II), and Zn(II) were 41%, 48%, 53%, and 63%, respectively. After bioreduction, Fe(II)/Cu(II) and Mn(II)/Zn(II) posed moderate and high risks, respectively. The results of this study will be useful to highlight the effects of variable redox conditions on the bioreduction process to determine the bioavailability of heavy metals in soil.