Objective The purposes is to estimate the average annual effective dose of the inhabitants and absorbed dose in some human tissues and organs arising from natural radiation sources in the High Background Radiation Area(HBRA) of Yangjiang and in the neighboring Control Area(CA). In order to provide more effective evidence for analyzing the dose effect relationships among the cohort members in the investigated areas, we divided the local inhabitant into different dose groups. Methods We measured the environmental gamma external radiation levels and individual accumulated doses of 5?293 people in the investigated areas. The concentrations for 222 Rn, 220 Rn and their decay products in air were also surveyed. We estimated the internal doses of natural radionuclides based on the results obtained from measurements in food, in drinking water, in human teeth, in several human tissues, in human placenta, and in activity concentration of exhaled 222 Rn and 220 Rn of the residents living in the investigated areas. Results The estimation of average annual effective doses in HBRA and CA based on the data of environmental measurements of radiation level respectively are 2.12±0.29 mSv a -1 and 0.69±0.09 mSv a -1 . The sources of higher background radiation in HBRA are mainly contributed from terrestrial gamma radiation. The estimation of average annual effective doses to the residents arising from inhalation of 222 Rn, 220 Rn and their decay products was 3.28 mSv a -1 in HBRA, while that in CA was 1.03 mSv a -1 . The values of the absorbed dose of the residents in their trachea bronchial tree and lung in HBRA arising from inhalation of 222 Rn, 220 Rn and their decay products are 5.40 mGy a -1 and 1.08 mGy a -1 respectively, which are about four times of the values of the absorbed dose in CA. The estimation of average annual effective doses to the inhabitants caused by 226 Ra and 228 Ra in HBRA and CA were 281.88 μ Sv a -1 and 84.54 μ Sv a -1 respectively. The annual absorbed doses to red bone marrow and bone lining cells of the inhabitants in HBRA were estimated to be 25.54 μ Gy a -1 and 140.46 μ Gy a -1 respectively for 226 Ra and 228 Ra respectively, while in CA were estimated 7.68 μ Gy a -1 and 42.25 μ Gy a -1 respectively. Conclusion The values of the effective dose of the inhabitants arising from natural radiation sources in HBRA and CA are 5.9 mSv a -1 and 2.0 mSv a -1 respectively. The value of the effective dose of the inhabitants arising from natural radiation sources in HBRA is about three times of the value in CA. There are 23718 individuals whose effective dose is 7 mSv a -1 . The values of the effective dose caused by internal radiation and external radiation in HBRA are 3.76 mSv a -1 and 2.12 mSv a -1 respectively. The amount of the effective dose of the residents arising from inhalation of 222 Rn, 220 Rn and their decay products consists of about 88 percent of the total amount of the internal radiation dose of the residents in HBRA. The estimate of average annual effective dose the residents arising from inhalation of 222 Rn and its decay products in HBRA was 1.53 mSv a -1 . The average annual effective dose of the residents arising from 220 Rn and its decay products in HBRA is 17.5 mSv a -1 ,which is 17.5 times of the worldwide average value 0.10 mSv a -1 . Thus, the 220 Rn and its decay products are one of the main sources to cause the internal radiation dose of the inhabitants living in HBRA.
Cytogenetic investigation of stable type aberrations (translocations) was performed with our improved methods in 6 children and 15 elderly persons in a high background radiation area (HBRA) in China, and in 8 children and 11 elderly persons in a control area. The total numbers of cells analyzed in elderly persons were 68,297 in HBRA and 35,378 in controls and in children were 45,535 in HBRA and 56,198 in controls. On average 5138 cells per subject were analyzed. The variation in the frequencies of translocations per 1000 cells was small in children while it was large in elderly persons. No significant difference was found in the frequencies between HBRA and control (P > 0.05, Mann-Whitney U test). On the other hand, correlation between age and translocation frequencies was significant at the 1% level (rs = 0.658 with 37DF, Spearman rank correlation test). The contribution of an elevated level of natural radiation in HBRA in China to the induction of stable type chromosome aberrations does not have a significant effect compared with the contribution of chemical mutagens and/or metabolic factors. The present study suggests that the probability of the risk of causing malignant and/or congenital diseases by the increased amount of radiation is imperceptible in HBRA where the level of natural radiation is 3 to 5 times higher than that in the control area.
As a part of the China-Japan cooperative research on natural radiation epidemiology, we have carried out a dose-assessment study to evaluate the external exposure to natural radiation in the high background radiation areas (HBRA) of Yangjiang in Guangdong province and in the control areas (CA) of Enping prefecture since 1991. Because of the difficulties in measuring the individual doses of all inhabitants directly by personal dosimeters, an indirect method was applied in which the exposed individual doses were estimated from the environmental radiation doses measured by survey meters and the occupancy factors of each hamlet. We analyzed the dose in the hamlets and the variation in the occupancy factors to obtain the parameters of dose estimation on the inhabitants in selected hamlets; Madi and several hamlets of different dose levels in HBRA and Hampizai hamlet in CA. With these parameters, we estimated individual dose rates and compared them with those obtained from direct measurement using dosimeters carried by selected individuals. The results obtained are as follows. 1) The environmental radiation doses are influenced by the natural radioactive nuclide concentrations in building materials, the age of the building and the arrangement of the houses in a hamlet. There existed a fairly large and heterogeneous distribution of indoor and outdoor environmental radiations. The indoor radiation doses were due to exposure from the natural radioactive nuclides in the building materials and were about two times as large as the outdoor radiation doses. The difference between indoor and outdoor doses was not observed in CA. 2) The occupancy factor was influenced by the age of individuals and by the season of the year. The occupancy factor was higher for infants and aged individuals than for other age groups. This lead to higher dose rates of exposure to those age groups. 3) A good correlation was observed between the dose assessed indirectly and that measured directly and the correlation factor was 0.97.
A historical cohort study was conducted in Misasa town, Tottori prefecture, Japan, where radon spas have been operating for a long time. Misasa town was divided into an elevated radon level area and a control area, with mean indoor radon levels of about 60 and 20 Bq/m3, respectively. In total, 3,083 subjects in the elevated radon level area and 1,248 in the control area, all aged 40 or older on January 1, 1976, were followed up until December 31, 1993, for a mean period of 14 years. The mortality rates from all causes exhibited no difference between the elevated radon level area and the control area for both sexes. No difference was observed in the incidence of all-site cancers (age, period-adjusted rate ratios by Poisson regression, RR = 1.06, 95% confidence interval (CI) 0.79-1.42 for males, RR = 0.90, 95% CI 0.65-1.24 for females), while stomach cancer incidence seemed to decrease for both sexes (RR = 0.70, 95% CI 0.44-1.11 for male, RR = 0.58, 95% CI 0.34-1.00 for female) and lung cancer incidence for males only seemed to increase (RR = 1.65, 95% CI 0.83-3.30 for male, RR = 1.07, 95% CI 0.28-4.14 for female) in the elevated radon level area. Caution is needed in the interpretation of these findings, however, since the individual exposure level was not measured and major confounding factors, such as smoking and diet, could not be controlled in this study.
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