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A few areas of the world show high levels of natural radiation, and one of these areas is located in Iran. Ramsar is a northern coastal town situated in the Caspian littoral (in Mazandaran province, Iran) on the slopes of the Alborz mountain range, and surrounded by forests. It is situated at 49° 40′ eastern longitude and 36° 53′ northern latitude. The area is rich with mineral springs. Investigations into the amount of radium-226 in water started more than 30 years ago.1 It has been reported that inhabitants of Ramsar receive an annual radiation absorbed dose from background radiation that is up to 260 mSv, substantially higher than the 20 mSv that is permitted for radiation workers.2
Annual births subdivided by gender, were obtained from Statistical Center of Mazandaran province. Because of the relatively small number of annual births in the urban area of Ramsar (currently about 670 per annum), analysis was carried out on the 11 year total for male and female live births, for the period 20 March 1989 to 19 March 2001, equal to Iranian calendar 1368 to 1379 Hejirae Shamsi (HS). The data was not available for the 1378 HS (equal to 20 March 1999 to 19 March 2000).
To test the null hypothesis that the probability of a male live birth in Ramsar is equal to that in the control populations, a χ2 test was conducted. A value of p < 0.05 was considered significant. The sex ratio is expressed as the proportion of total live births that were males.
The sex ratios at birth in the urban area of Tonekabon, the nearest city to Ramsar (about 20 km distance) and the urban areas of Mazandaran province (excluding Ramsar) were used as controls. The overall sex ratios in Ramsar, Tonekabon, and the urban areas of Mazandaran province were 0.511 (total live births = 7591), 0.517 (total live births = 14 266), and 0.509 (total live births = 253 918), respectively. There was no significant difference between Ramsar and either Tonekabon (χ2 = 0.95, df = 1, p = 0.33) or urban areas of Mazandaran province (χ2 = 0.13, df = 1, p = 0.71).
It has been reported that the sex ratio in the offspring of male radiologists is significantly lower than that in control populations.3 However, this is not consistent with the present result. This discrepancy could be attributed to the exposure of both parents to ionising radiation. Alternatively, because the inhabitants of Ramsar have lived for many generations in an area of high background radiation, some kind of adaptation might have occurred.
This study was supported by Shiraz University