How Phosphate Ion Influences Cycling of Carbon and Iron in the Environment
Subsurface microbes convert iron among several chemical species. These forms of iron can influence the immobilization and release of contaminant metals such as uranium as well as sequestration of carbon. Predictive understanding of the processes involved in these transformations is limited by a lack of knowledge of the impact of many other chemical species commonly found with iron in the subsurface. New research by scientists at Argonne National Laboratory and collaborating universities has provided knowledge of how phosphate ion incorporated in iron-containing minerals affects the speciation of iron and cycling of carbonate ion (a common form of carbon in the subsurface). These scientists determined that the phosphate bound or occluded within the Fe(III)-containing particles has a significant impact on the minerals produced by the iron-reducing bacterium Shewanella putrefaciens . In the absence of phosphate, the Fe(III) is largely converted to magnetite, but when phosphate is present within the Fe(III) particles, a significant amount of a reactive iron-containing species known as green rust is produced. Green rust is highly effective in reducing and immobilizing contaminants such as radionuclides and toxic metals. This study therefore provides key information for understanding how to efficiently use Shewanella to treat contaminated environments.
O’Loughlin, E. J., M. I. Boyanov, T. M. Flynn, C. Gorski, S. M. Hofmann, M. L. McCormick, M. M. Scherer, and K. M. Kemner. 2013. “Effects of Bound Phosphate on the Bioreduction of Lepidocrocite (γ-FeOOH) and Maghemite (γ-Fe2O3) and Formation of Secondary Minerals,” Environmental Science and Technology 47 , 9157–66. DOI: 10.1021/es400627j.