residents and regulatory control of new construction. The radioactivity is due to the local geology. Underground water dissolves radium in uraniferous igneous rock and carries it to the surface through at least nine known hot springs. These are used as spas by locals and tourists. Some of the radium precipitates into travertine, a form of limestone, and the rest diffuses into the soil, where it is absorbed by crops and mixes with drinking water. Residents have unknowingly used the radioactive limestone as a building material for their homes. The stone irradiates the inhabitants and generates radon gas which is usually seen to promote lung cancer. Crops contribute 72 µSv/yr to a critical group of 50 residents. International relations Twin towns and sister cities Ramsar is twinned with: Puerto Montt, Chile (Since 28 January 2009) Al Wakrah, Qatar (Since 14 June 2010) Shiraz, Iran (Since 9 January 2013) Notable people Mohammad Reza Khalatbari (b. 1983) - Football player Esfandiar Rahim Mashaei (b. 1960) - Politician Hossein Khalatbari (1949-1985) - Iranian fighter pilot Elika Abdolrazzaghi (b. 1979) - Cinema, stage and TV actress Mohammad-Ali Taskhiri (1948-2020) - Iranian cleric and diplomat Rahim Ebadi (b. 1957) - Politician Gallery See also Rejuvenation (aging) Background radiation Banana equivalent dose History of Iran Tourism in Iran International rankings of Iran References External links Ramsar's tourism Ramsar's radioactivity Photos of Ramsar (Permission to use and copy these photos is hereby granted provided the above copyright notice appears in all the copies and modified versions of photos.) Cities in Mazandaran Province Populated coastal places in Iran Populated places on the Caspian Sea