en Radiation Biology Radiation Biology تحقيق بديع Original Research <div style="text-align: justify;">Background: One of the most significant radionuclides in natural drinking waters is ²²⁶Ra and its decay products. It is potential of health problems, including cancer risk. In this study, the effect of ²²⁶Ra concentration in 28 drinking water samples collected from the North Guilan province was investigated. Materials and Methods: The activity concentrations of ²²⁶Ra were measured by using of radon emanation method and Pylon AB-5 radon scintillation detector. The annual effective dose distribution by age groups, radiological risk and chemical toxicity risk were calculated in drinking water. &nbsp;Results: The activity concentration results range from a low limit of detection (LLD) 2.0&plusmn;0.1 mBq l^-1 to 38.2&plusmn;2.4 mBq l^-1. Also, the annual effective dose distribution by age groups estimated results were from 1.8&times;10^-6Sv y^-1for adults to 1.5&times;10^-5Sv y^-1for infants. &nbsp;The radiological risk assessment results were 1.06&times;10^-6 to 2.03&times;10^-5 for morbidity risk, 7.32&times;10^-7 to 1.40&times;10^-5 for mortality risk. The chemical toxicity risk results obtained from 1.08&times;10^-1 to 5.63&times;10^-3. Conclusion: The activity concentration level of ²²⁶Ra in all drinking water samples were less than the recommended level WHO for drinking water 1000 mBq l^-1. Meanwhile, annual effective dose level, cancer morbidity, mortality risk and life annual daily dose due to consumption of selected drink water samples were less than the standard limit.</div> Ra-226 radionuclide, drinking waters, radiological risk, chemical toxicity, cancer. 163 169 http://ijrr.com/browse.php?a_code=A-10-1-769&slc_lang=en&sid=1 A. Abbasi akbar.abbasi@emu.edu.tr 7900319475328460012745 7900319475328460012745 Yes University of Kyrenia, Girne, TRNC, via Mersin 10, Turkey F. Mirekhtiary 7900319475328460012746 7900319475328460012746 No Near East University, Nicosia, North Cyprus, Mersin 10, Turkey