It is one of the most toxic substances known to man and has been used to poison kings, emperors and even prize winning racehorses.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/people-who-can-eat-arsenic-remote-village-andes-found-have-developed-tolerance-toxic-chemical
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/daily-mail-united-kingdom
[3] http://admin.indiaenvironmentportal.org.in/category/thesaurus/environment
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/arsenic
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/health
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/argentina
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/drinking-water
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/water-quality