"environmental: Toxic chemicals are sometimes produced in the process. Sulfuric acid and H+ ions that have been formed can leak into the ground and surface water turning it acidic, causing environmental damage. Heavy ions such as iron, zinc, and arsenic leak during acid mine drainage. When the pH of this solution rises, as a result of dilution by fresh water, these ions precipitate, forming ""Yellow Boy"" pollution. For these reasons, a setup of bioleaching must be carefully planned, since the process can lead to a biosafety failure. "