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Breathing toxic selenium and arsenic oxyanions: Microbes, Mono Lake, and Mars

Ron Oremland, Ph.D.
U.S. Geological Survey

Wednesday, September  20, 2000
3:00 p.m.—Pacific Forum

                                             Mono Lake

Oxyanions of selenium and arsenic occur in waters as a consequence of human activities, or from natural sources. These toxic elements have biogeochemical cycles mediated by microorganisms. An important discovery was that certain bacteria achieve anaerobic growth using selenate or arsenate as oxidants, forming elemental selenium or arsenite. These results have geochemical significance, and the phenomenon may be exploited to remove these toxins from contaminated waters and soils.

We investigated Mono Lake because it has high levels of hydrothermally derived arsenate (~ 200 μM) in its alkaline and saline waters. Bacterial respiration of arsenate in the anoxic waters mineralizes as much as 14 % of the lake’s annual primary production. If microbial life existed on the volcanically active surface of Mars some 3 billion years ago, this finding has implications for the possible types of respiration occurring in its shrinking haloalkaline lakes.

Next: The other Doc—J.B. Phillips and the California Department of Fish and Game