Accumulation of Metals by Bacteriogenic Iron Oxides in a Subterranean Environment

Bacteriogenic iron oxides (BIOS) and groundwater samples were collected from 66 to 432 m underground at the Aspo Hard Rock Laboratory near Oskarshamn, Sweden. The twisted, iron oxide-encrusted stalks of the lithoautotrophic ferrous iron-oxidizing bacterium Gallionella ferruginea were prominent in the BIOS samples. A wide variety of heterotrophic bacteria, including stalked forms resembling Caulobacter or Hyphomicrobium species, were also present. Energy dispersive x-ray spectroscopy, selected area electron diffraction, and x-ray diffraction analyses confirmed that the BIOS samples contained only poorly ordered (amorphous) hydrous ferric oxide. Inductively coupled plasma emission spectroscopy revealed iron oxide contents that varied from 60% to 90% (dry weight basis). Metal concentrations in filtered groundwater ranged from 10mM for Na to 10 -4 mM or less for Co, Cu, Cr, and Zn. Intermediate concentrations were recorded for Fe and Mn ( 10 -2mM). Solid-phase metal concentrations in the BIOS spanned the 10 -...