TOXICITY OF HEAVY-METALS (NI,ZN) TO DESULFOVIBRIO-DESULFURICANS

This study is the first to address systematically five important facto rs necessary to quantify the toxicity of heavy metals to sulfate-reduc ing bacteria: metal precipitation due to reaction with components in t he media; metal adsorption onto solid phases; precipitation of metal s ulfides due to reaction with sulfide initially present in an active mi crocosm; quantification of initial metal concentrations; and aqueous m etal complexing, which reduces metal bioavailability. The toxicity of Ni and Zn To pure cultures of Desulfovibrio desulfuricans was quantifi ed using a chemically defined medium at pH 7.2. Free heavy metal ion a ctivity 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 attem pts to remediate Ni and/or Zn contamination by bacterial sulfate reduc tion are likely to be successful only if total Ni + Zn activity is bel ow this level in order to prevent heavy metal toxicity.