[The Conversation Africa] For 140 years, gold mines in Johannesburg, South Africa have been leaking wastewater contaminated with heavy metals. The acid mine drainage from Johannesburg's estimated 278 abandoned mines and 200 mine dumps includes uranium (a radioactive metal), toxic arsenic, copper, cobalt, nickel, lead and zinc. Acid mine drainage can pollute land and water sources up to 20 kilometres away from a mine unless it is remediated by mining companies. The contamination cascades through food webs and poisons river water,
