Amalgam (chemistry) gold") would not be extractable from ore using hydro-mechanical methods. Large amounts of mercury were used in "placer mining", where deposits composed largely of decomposed granite slurry were separated in long runs of "riffle boxes", with mercury dumped in at the head of the run. The amalgam formed is a heavy solid mass of dull gray color. (The use of mercury in 19th century placer mining in California, now prohibited, has caused extensive pollution problems in riverine and estuarine environments, ongoing to this day.) Sometimes substantial slugs of amalgam are found in downstream river and creek bottoms by amateur wet-suited
Dental amalgam controversy they contain Bis-phenol A (BPA) a chemical known to cause reproductive toxicity at high doses. In Canada, amalgam use is considered safe and effective. A 2005 position statement from the Canadian Dental Association (CDA) states that "current scientific evidence on the use of dental amalgam supports that amalgam is an effective and safe filling material that provides a long-lasting solution for a broad range of clinical situations. The CDA has established its position based on the current consensus of scientific and clinical experts and on recent extensive reviews of strong evidence by major North American and international organizations, which have