Toxicity of heavy metals (Ni,Zn) to Desulfovibrio desulfuricans

This study is the first to address systematically five important factors necessary to quantify the toxicity of heavy metals to sulfate-reducing bacteria: metal precipitation due to reaction with components in the media; metal adsorption onto solid phases; precipitation of metal sulfides due to reaction with sulfide initially present in an active microcosm; quantification of initial metal concentrations; and aqueous metal complexing, which reduces metal bioavailability. The toxicity of Ni and Zn To pure cultures of Desulfovibrio desulfuricans was quantified using a chemically defined medium at pH 7.2. Free heavy metal ion activity was calculated using MINTEQA2 and an amended database. A total activity of Ni2+(aq) + Zn2+(aq) greater than approximately 2.5 x 10(-5) molal is toxic to D. desulfuricans. The results indicate that attempts to remediate Ni and/or Zn contamination by bacterial sulfate reduction are likely to be successful only if total Ni + Zn activity is below this level in order to prevent heavy metal toxicity.