|Fig. 1: Location of Ramsar in Iran. (Source: Wikimedia Commons)|
Ramsar, a city on the northern coast of Iran (Fig. 1), has some of the highest known levels of naturally occurring background radiation in the world. In some areas of the city, the background radiation is around 260 mSv per year, which is much higher than the 20 mSv per year limit set for radiation workers in Iran.  These incredibly high levels of radiation mostly stem from the presence of high levels of Ra-226 brought to the surface through natural hot springs. Water is heated by geological activity under the Earth's surface and is then travels through rocks containing radioactive substances. Nine hot springs lie within the city and they all have varying levels of radiation, leaving the city itself with some areas having normal levels of background radiation and some areas with very high radiation levels. The residents of Ramsar use these hot springs as health spas, and those who live near the hot springs use materials from them to build their homes. The erosion of local bedrock with a high Thorium content also contributes to the high radiation levels. [1,2] This radiation is also present in the local food supply at levels about 12 times greater than the average levels of radiation in food. 
With such high levels of background radiation, the residents of Ramsar are the perfect subjects for studies relating to the chronic exposure to radiation on humans. In one study, those who live in areas of Ramsar with higher levels of background radiation were found to have around 56% of the average amount of genetic abnormalities than those who lived in areas with normal background radiation.  There were also no significant differences between the immune systems of those living in areas with high radiation and average radiation, except for slightly reduced levels of Immunoglobulin A and Immunoglobulin G in those living in areas with more radiation.  This could possibly signify that when exposed to radiation long-term that it could in fact be beneficial in eliciting an adaptive response. This also directly contradicts the linear no-threshold model for radiation exposure. Those who lived in higher radiation areas also were found to live the same life expectancy as those in lower radiation areas, while all residents of Ramsar had the same life expectancy as those in neighboring areas with less background radiation. [1,3]
Not only were there fewer instances of chromosomal abnormalities in these areas, but one study found that the risk of lung cancer was actually lower in the areas with higher radiation. Radon exposure is widely accepted as a risk factor for lung cancer, yet in the areas of Ramsar with average levels of Radon, there was a significantly greater presence of lung cancer than in the areas with the highest Radon concentrations.  Another study investigating cancer with respect to the differences in tumor biomarkers in those who live in higher background radiation areas (HBRAs) and normal background radiation areas (NBRA) of Ramsar found that the differences in most tumor biomarkers was not significant. Five out of the eight biomarkers, (PSA, CA15.3, CA125, CA19.9, and AFP) did not have significantly different concentrations between those from HBRAs and NBRAs. However, concentrations of the biomarkers Cyfra21, CEA, and Tag72 were higher in the HBRA group than in the NBRA group. 
While there are some seemingly negative changes at the cellular level in those who live in HBRAs, there overall do not appear to be any negative changes in the overall health in the individuals living in these areas. If anything, it appears that exposure to these levels of background radiation over time could be beneficial in eliciting an adaptive response.  It would be interesting to further investigate the genetics of the individuals involved over time to see if those who live in these areas have evolved to withstand such high levels of background radiation over generations or if chronic exposure to this radiation has acclimated them to it.
© Sydney Lance. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
 M. Ghiassi-Nejad et al., "Very High Background Radiation Areas of Ramsar, Iran: Preliminary Biological Studies," Health Phys., 82, 87 (2002).
 O. Selinus, R. B. Finkelman, and J. A. Centeno, eds., Medical Geology: A Regional Synthesis (Springer, 2010).
 S. M. J. Mortazavi and H. Mozdarani, "Non-Linear Phenomena in Biological Findings of the Residents of High Background Radiation Areas of Ramsar," Int. J. Radiat. Res. 11, 3 (2013).
 S. M. J. Mortazavi, M. Ghiassi-Nejad, and M. Rezaiean, "Cancer Risk Due to Exposure to High Levels of Natural Radon in the Inhabitants of Ramsar, Iran," Int. Congr. Ser. 1276, 436 (2005).
 S. Taeb et al. "Alterations of PSA, CA15.3, CA125, Cyfra21-1, CEA, CA19.9, AFP and Tag72 Tumor Markers in Human Blood Serum Due to Long Term Exposure to High Levels of Natural Background Radiation in Ramsar, Iran ," Int. J. Radiat. Res. 12, 123 (2014).