The potential health hazards of chronic exposure to low-dose natural radioactivity in Terengganu, Malaysia

摘要

Measurement of terrestrial gamma radiation dose (TGRD) rate and activity concentrations of naturally occurring radionuclides in environmental media such as soil and air play an important role in the setting national average permissible doses to members of public. Malaysia is planning to add nuclear energy to its national electricity grid; hence the knowledge of the levels of exposure to natural background radioactivity is important for policies and law making with regards to radiological protection of both human and the environment. The aim of this work was to measure the variation of background radiation with respect to geological formations of Terengganu (Malaysia) and assess the potential health hazards that are associated with the chronic exposure to natural radiation in the area. Ludlum 19 micro survey meters with NaI[Tl] detectors and HPGe gamma ray spectrometer were used for in situ TGRD and laboratory analysis, respectively. The measured TGRD rates ranged from 35 to 340 nGy h(-1) with mean value of 150 nGy h(-1) and the annual effective dose to population was 0.92 mSv year(-1). The mean (range) activity concentrations of Ra-226, Th-232, and K-40 in the soil samples were 79 +/- 3 (20 +/- 1-151 +/- 5) Bq kg(-1); 84 +/- 3 (8 +/- 1-182 +/- 6) Bq kg(-1); and 545 +/- 55 (47 +/- 5-1056 +/- 107) Bq kg(-1), respectively. Upon comparing these values with the world averages for specific activities of Ra-226, Th-232 and K-40 (i.e. 33, 36 and (474)Bq kg(-1) for Ra-226, Th-232 and K-40 respectively), It is revealed that the mean activity concentrations of Ra-226 and Th-232 in the soil of Terengganu are higher than the world averages by a factor of two. The mean activity concentration of 40 K in the soil of Terengganu is similar to 15 % higher than the world average. Acid intrusive geological formation (due to the granite composition from igneous rocks), which is the most dominant in the state was found to contained higher mean TGRD values as well as Ra-226 and Th-232 concentration this was consistent with some previous studies.