Does short-term exposure to elevated levels of natural gamma radiation in Ramsar cause oxidative stress?

BACKGROUND Ramsar, a city in northern Iran, has areas with some of the highest recorded levels of natural radiation among inhabited areas measured on the earth. AIMS To determine whether short-term exposure to extremely high levels of natural radiation induce oxidative stress. MATERIALS AND METHODS In this study, 53 Wistar rats were randomly divided into five groups of 10-12 animals. Animals in the 1(st) group were kept for 7 days in an outdoor area with normal background radiation while the 2(nd) , 3(rd) , 4(th) and 5(th) groups were kept in four different outdoor areas with naturally elevated levels of gamma radiation in Ramsar. A calibrated RDS-110 survey meter, mounted on a tripod approximately 1 m above the ground, was used to measure exposure rate at each location. On days 7 and 9 blood sampling was performed to assess the serum levels of catalase (CAT) and malondialdehyde (MDA). On day 8, all animals were exposed to a lethal dose of 8 Gy gamma radiations emitted by a Theratron Phoenix (Theratronics, Canada) Cobalt-60 (55 cGy/min) at Radiotherapy Department of Razi Hospital in Rasht, Iran. RESULTS Findings obtained in this study indicate that high levels of natural radiation cannot induce oxidative stress. CAT and MDA levels in almost all groups were not significantly different (P = 0.69 and P = 0.05, respectively). After exposure to the lethal dose, CAT and MDA levels in all groups were not significantly different (P = 0.054 and P = 0.163, respectively). CONCLUSIONS These findings indicate that short-term exposure to extremely high levels of natural radiation (up to 196 times higher than the normal background) does not induce oxidative stress.