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WWRC 97-05aaa
Assessment of Copper Mobilization Resulting From Reduction of Iron Oxide


Microorganisms can greatly influence heavy metal mobility by reductively dissolving iron oxides and liberating adsorbed heavy metals; however, the toxicity of remobilized heavy metals to iron-reducing bacteria is unknown. We hypothesize that resistance to metals like copper enables bacteria to reduce more copper-complexed iron oxide than bacteria lacking resistance; the effect of which is increased remobilization of heavy metals in relation to increased resistance.

Resistance should be a function of exposure history to heavy metals with the more metal-resistant bacteria having been previously exposed to heavy metals. We have cultured iron-reducing bacteria from the Rio Calveras in the Jemez Mountains of New Mexico for use as a pristine enrichment. We also cultured iron reducers from the heavy metal-contaminated Milltown reservoir in southwestern Montana. Both pristine and heavy metal-contaminated enrichments were used to assess how previous exposure to metals influences the release of a toxic metal adsorbed to iron oxide.

Using iron oxide without adsorbed copper, iron reducing enrichments from both environments were relatively similar with regard to extent of total iron reduced. In the presence of copper, however, bacteria previously exposed to copper exhibited resistance with regard to total iron reduced relative to bacteria having no previous history with copper. A general linear model describing over 98% of the variation in total iron reduced is described for bacteria that differ in their copper exposure history and the presence or absence of copper. We will present the results of further copper mobilization studies using these major controlling variables.

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