Coupled Kinetics Model for Microbially Mediated Arsenic Reduction and Adsorption/Desorption on Iron Oxides: Role of Arsenic Desorption Induced by Microbes

The dynamic behavior of arsenic (As) species is closely associated with iron mineral dissolution/transformation in the environment. Bacterially induced As­(V) desorption from iron oxides may be another important process that facilitates As­(V) release from iron oxides without significant reductive dissolution of iron oxides. Under the impact of bacterially induced desorption, As kinetic behavior is controlled by both the microbial reduction of As­(V) and the As­(III)&As­(V) reactions on iron oxide surfaces. However, there is still a lack of quantitative understanding on the coupled kinetics of these processes in complex systems. We developed a quantitative model that integrated the time-dependent microbial reduction of As­(V) with nonlinear As­(III)&As­(V) adsorption/desorption kinetics on iron oxides under the impact of bacterially induced As­(V) desorption. We collected and modeled literature data from 11 representative studies, in which microbial reduction reactions occurred with minimal iron oxide dissolution/transformation. Our model highlighted the significance of microbially induced As­(V) desorption and time-dependent changes of microbial reduction rates. The model can quantitatively assess the roles and the coupling of individual reactions in controlling the overall reaction rates. It provided a basis for developing comprehensive models for As cycling in the environment by coupling with other chemical, physical, and microbial processes.