Background radiation exposure varies hugely, from an annual average of 2.2 millisieverts in the UK to above 30 millisieverts in the Indian state of Kerala (pictured) and the city of Chennai, and as high as 40 millisieverts in parts of Brazil and Sudan, according to the World Nuclear Association.
It all depends on local geology. India, for example, has large amounts of radioactive thorium in its soil. The province of Ramsar in Iran has hot springs full of dissolved radium-226, making it the most naturally radioactive place in the world, with doses up to 250 millisieverts a year, five times the permitted dose for American radiation workers.
The dosage limits do not include background radiation. Even though background radiation varies by location.
It is not clear if a nuclear industry worker who vacations in the Brazil or Sudan would have the extra background radiation that they experience there counting against their dosage limit.
World Nuclear Association on radiation and health
US Dosage Limits
50 millisieverts is the maximum yearly dose for nuclear industry workers.
5 millisieverts is the maximum yearly dose for regular civilians in the USA.
UK Dosage Limits
The UK limits on effective dose (dose to the whole body) introduced by the IRR99 to replace the limits set previously by the IRR85 are:
* for employees aged 18 years or over, 20 millisieverts in a calendar year (except that in special cases employers may apply a dose limit of 100 millisieverts in 5 years with no more than 50 millisieverts in a single year, subject to strict conditions);
* for trainees, 6 millisieverts in a calendar year; and
* for any other person, including members of the public and employees under 18 who cannot be classed as trainees, 1 millisievert in a calendar year.
Background radiation is discussed in a previous Nextbigfuture article
Ramsar, Iran Radioactivity
Wikipedia on Ramsar
Some areas around Ramsar have the highest level of natural radioactivity in the world, due to the presence of radioactive hot springs. In the high-background radiation districts of Ramsar, the average dose of radiation received by a person for one year is about 10 mSv, and can reach levels in excess of 260 mSv.
The highest levels of background radiation recorded in the world to date is from areas around Ramsar, particularly at Talesh-Mahalleh which is a very high background radiation area (VHBRA) having an effective dose equivalent several times in excess of ICRP-recommended radiation dose limits for radiation workers and up to 200 times greater than normal background levels. Most of the radiation in the area is due to dissolved radium-226 in water of hot springs along with smaller amounts of uranium and thorium due to travertine deposits. There are more than nine hot springs in the area with different concentrations of radioisotopes, and these are used as spas by locals and tourists. This high level of radiation does not seem to have caused ill effects on the residents of the area and even possibly has made them slightly more radioresistant, which is puzzling and has been called "radiation paradox".
Moreover some studies showed fewer chromosome aberrations in Ramsar's inhabits when Lymphocytes are exposed to high gamma radiations. This indicate that inhabitants of Ramsar are more radioresistant compared to residents in other areas. Prof Mortazavi supposes that genetic modifications have occurred in the time span of a lot of generations to induce the radioresistance.
It has also been claimed that residents have healthier and longer lives. On the basis of this and other evidences including the fact that life had originated in a much more irradiated environment, some scientists have questioned the validity of linear no-threshold model, on which all radiation regulations currently depend. Others point out that some level of radiation might actually be good for health and have a positive effect on population based on radiation hormesis model, by jump starting DNA repair mechanisms inside the cell. Due to consumption of radioactive water around Ramsar, the agricultural products as well as other living matter and humans are also slightly radioactive.
However, the small size of the population (only 1800 inhabitants in the high-background areas) makes it difficult to draw definitive conclusions regarding their cancer epidemiology data. Furthermore, there are questions regarding possible non-cancer effects of the radiation background. An Iranian study has shown that people in the area have a significantly higher expression of CD69 gene and also a higher incidence of stable and unstable chromosomal aberrations. Chromosomal aberrations have been found in other studies and a possible elevation of female infertility has been reported
Kerala's coastal belt of Karunagappally is known for high background radiation from thorium-containing monazite sand. In coastal panchayats, median outdoor radiation levels are more than 4 mGy/yr and, in certain locations on the coast, it is as high as 70 mGy/yr. (1 mSv is the dose produced by exposure to 1 milligray (mG) of radiation). So 4 milliSievert to 70 milliSievert.
Kerala's population more than doubled between 1951 and 1991 by adding 15.6 million people to reach 29.1 million residents in 1991, the population stood at less than 32 million by 2001. Kerala's coastal regions are the most densely settled, leaving the eastern hills and mountains comparatively sparsely populated.
Over 140,000 inhabitants in Kerala, on the southwest coast of India, receive an annual average dose of 15-25 mGy (15-25 milliSv)(Kesavan 1997). The average life span of the inhabitants of Kerala is 72 years while for all India it is only 54 years (Goraczko 2000 and its citations). A comprehensive study on the residents of HLNRAs of Kerala showed no evidence that cancer incidence is consistently higher because of the levels of external gamma radiation exposure in the area (Nair et al. 1999).
About 2.5 million people live in Yangjiang. They get about 6.4 mSv in background radiation area (HBRA) in Yangjiang, China.
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