Application of grading evaluation method of water radioactivity level in Chongqing section of Yangtze River.

The major rivers in a region are usually vital sources of drinking water for local populations, and the concentration of radionuclides in the water is intimately tied to people's health. The varying concentration limits set by the World Health Organization are appropriate as screening values for determining the pollution of water sources, but their capacities as regulatory or early warning limits are restricted. In daily management, the regulatory authority needs to manage water bodies by level based on the concentration of radionuclide to indicate the potential pollution risks. From 2017 to 2019, a statistical analysis and dosage evaluation were conducted on the water radioactivity level in the Chongqing section of the Yangtze River in this study. The Modified Nemerow Index method based on the dose conversion coefficients was applied for the grading evaluation of the water radioactivity level, allowing the grading effect discussed. The results showed that the concentration of radionuclides in the Chongqing section of the Yangtze River and its contribution to the annual effective dose of the human body were lower than the limits stated in the Guidelines for Drinking Water Quality (Fourth Edition). And the samples in the section were 52.94% in Grade Ⅰand 47.06% in Grade Ⅱ, meaning few potential radioactive pollution risks exist there. Compared with other methods. The Modified Nemerow Index method combines the Traditional Nemerow Index method with the dose conversion coefficient of nuclides making it more realistic for the early warning and control of radioactive pollution in water bodies, which is worth popularizing and implementing.

IMPACT OF THE THREE GORGES WATER CONSERVANCY PROJECT ON RADIOACTIVITY CONCENTRATION LEVELS IN SURROUNDING WATERS.

Large-scale water conservancy projects bear much economic and social significance. However, there is a lack of systematic research on how such projects affect radioactivity levels in regional water bodies. For the first time, the present paper uses data for nearly 10 y at different impoundment levels during construction of the dam to analyze changes in water radioactivity concentration levels in China's Three Gorges region, in order to provide a valuable reference for evaluating the impact of large-scale water conservancy projects on radioactivity concentration levels. Results show that gross α, gross ß, U, Th, 226Ra, 40K, 90Sr and 137Cs levels in the water bodies of the Three Gorges region fall within normal limits and annual effective dose for the adults, children and infants are below the WHO recommended reference level of 0.1 mSv per y. The period where the sample was collected and spatial distribution are the main reasons why some radionuclides are not normally distributed. Different water levels during different periods result in large variations in the levels of certain radionuclides, indicating that water levels can have a strong influence on radionuclide levels in reservoir regions. Hence, when evaluating the impact of large-scale water conservancy projects on radioactivity levels, analysis should be carried out on samples collected during different periods in order to make accurate assessments.