The differential inhibitive effects and fates of As(III) and As(V) mediated by Sulfobacillus thermosulfidooxidans grown on S, Fe and FeS.

Arsenic often coexists with metal sulfide minerals and occurs in different speciation and different toxicity in responding to Fe/S biooxidation. The differential inhibitive effects and fates of As(III) and As(V) during biooxidations of elemental sulfur (S), ferrous ions (Fe) and pyrite (FeS) by Sulfobacillus thermosulfidooxidans were studied. The results revealed that the arsenic species hardly changed for the biooxidation of S, but dramatically changed for the biooxidation of Fe and FeS. Different transformation degree between As(III) and As(V) occurred for biooxidation of FeS in the presence of arsenic, where about 72% of As(III) was transformed to As(V) for the group with As(III) added, and 16% of As(V) was transformed to As(III) for that with As(V) added. Both formation and dissolution of amorphous ferric arsenate occurred during biooxidation of FeS with the addition of As(III) or As(V) and for the group grown on Fe with added As(V), which were controlled by the changes of Fe/As molar ratio and pH value in the solution. Jarosite was detected for the group grown on Fe and could adsorb As(III) and As(V). The inhibitive effects of As(V) were higher than As(III) when the strain grew on FeS, which was contrary to those when the strain grew on S and Fe. The above results signify that the fates and inhibitive effects of arsenic are much related to each other, and such a relationship is significantly affected by the utilization of Fe/S energy substrates by the sulfur- and ferrous-oxidizing microorganisms.