The demon quicksilver: clandestine gold mining is a major source of mercury contamination

 
 Most mercury is not recycled, so the artisanal gold mining is a major source of environmental pollution. Mercury and artisanal gold mining When mercury and gold contact, even if the gold is still in a pellet or crushed ore, forming a mixture or an "amalgam" of equal parts of metal. This is especially useful when fine particles of gold in river sediments and is therefore invisible to the naked eye. To recover gold from the amalgam, the mixture must be subjected to high temperatures to evaporate the mercury and it is only gold. Therefore, mercury contamination can occur at several points in the process. Inappropriate storage or handling, overuse and during the last step of evaporation Mercury is a powerful neurotoxin and can cause a variety of chronic symptoms and congenital deformities especially in developing fetuses and young children. 
http://es.mongabay.com/news/2014/es1116-watsa-gold-mining-responsible-for-mercury-pollution.html