Some areas of the world, called high background radiation areas (HBRAs), have anomalously high levels of background radiation. In such terrains, the geology and geochemistry of the rocks and minerals have the greatest influence in determining where the high natural radiation shows up. Ramsar, a city in northern Iran, has one of the highest natural-radiation levels in the world. In some locations at Ramsar, the radiation level is 55 to 200 times higher than the background level.
The most interesting feature in all these cases is that the people living in these HBRAs do not appear to suffer any adverse health effects as a result of their high exposures to radiation. On the contrary, in some cases the individuals living in these HBRAs appear to be even healthier and to live longer than those living in control areas that are not classified as HBRAs. These phenomena pose many intriguing questions for medical geologists. Chandra Dissanayake, a senior professor of geology at the University of Peradeniya, Sri Lanka, has pioneered geochemical research in Sri Lanka.