Biooxidation of elemental sulfur, arsenopyrite and pyrite were studied to investigate the role of bacteria in the mechanism of environmental contamination by sulfuric acid and arsenic, which takes place in sulfide mine wastes and deposits. Oxidation of elemental sulfur by free and adsorbed bacteria Acidithiobacillus ferrooxidans was characterized by kinetic and physiological parameters. The primary product of arsenopyrite biooxidation was arsenite. Its oxidation by ferric iron to less toxic arsenate at a low pH could be detected only under catalysis of pyrite and A. ferrooxidans. Electrochemical studies on pyrite oxidation to sulfuric acid by A. ferrooxidans resulted in the occurrence of sulfate ions without the formation of sulfur intermediates.