a process for the decontamination of a medium including a particulate material contaminated with one or more organic species and one or more metal species , the process including the steps of : treating said medium by breaking down the organic species by or through the action of microbial agents , treating the medium with microbially produced sulfuric acid so as to solubilize and leach the metal species as a metal sulfate , treating the leached metal sulfate by a bioprecipitation process which converts the said sulfate into one or more insoluble metal sulfides and hydrogen sulfide , separating the hydrogen sulfide from the one or more insoluble metal sulfides and oxidizing the separated hydrogen sulfide to form a reusable source of a sulfur - containing ingredient .