A unique high natural background radiation area - Dose assessment and perspectives.

The biological effects of low dose-rate radiation exposures on humans remains unknown. In fact, the Japanese nation still struggles with this issue after the Fukushima Dai-ichi Nuclear Power Plant accident. Recently, we have found a unique area in Indonesia where naturally high radiation levels are present, resulting in chronic low dose-rate radiation exposures. We aimed to estimate the comprehensive dose due to internal and external exposures at the particularly high natural radiation area, and to discuss the enhancement mechanism of radon. A car-borne survey was conducted to estimate the external doses from terrestrial radiation. Indoor radon measurements were made in 47 dwellings over three to five months, covering the two typical seasons, to estimate the internal doses. Atmospheric radon gases were simultaneously collected at several heights to evaluate the vertical distribution. The absorbed dose rates in air in the study area vary widely between 50 nGy h-1 and 1109 nGy h-1. Indoor radon concentrations ranged from 124 Bq m-3 to 1015 Bq m-3. That is, the indoor radon concentrations measured exceed the reference levels of 100 Bq m-3 recommended by the World Health Organization. Furthermore, the outdoor radon concentrations measured were comparable to the high indoor radon concentrations. The annual effective dose due to external and internal exposures in the study area was estimated to be 27 mSv using the median values. It was found that many residents are receiving radiation exposure from natural radionuclides over the dose limit for occupational exposure to radiation workers. This enhanced outdoor radon concentration might be as a result of the stable atmospheric conditions generated at an exceptionally low altitude. Our findings suggest that this area provides a unique opportunity to conduct an epidemiological study related to health effects due to chronic low dose-rate radiation exposure.

Ocular lens opacity in residents of areas with high natural radiation background in Yangjiang City, China / 中国职业医学

OBJECTIVE: To investigate the effects of long-term and low dose ionizing radiation on ocular lens opacities of residents living in areas with high natural radiation background(HNRB) in Yangjiang City, China. METHODS: A total of 483 Han residents from Yangjiang City(HNRB area) and 517 from Enping City(control area) were selected as study subjects using a cluster random sampling method. Questionnaire survey and lens examination were carried out. The risk factors of lens opacity and its severity were analyzed by logistic regression analysis. RESULTS: The prevalence rates of lens opacity, cortical opacity and posterior subcapsular opacity in HNRB area were higher than those in control area(60.7% vs 51.6%, 53.4% vs 46.8%, 21.9% vs 9.3%, all P<0.05). There was no significant difference in karyotype turbidity between HNRB area and control area(52.4% vs 47.6%, P>0.05). After adjusting for confounding factors including age, gender, cardiovascular/metabolic diseases, smoking, alcohol drinking and tea drinking, the unconditional logistic regression analysis results showed that the risk of ocular opacity, cortical opacity and posterior subcapsular opacity in residents of HNRB area was higher than that in control area(all P<0.05). Multivariate disordered logistic regression analysis results showed that residents in the HNRB area had a higher risk of grade two karyotype turbidity than grade one karyotype turbidity(P<0.01). Ordered logistic regression analysis results showed that residents in HNRB area had an increased risk of developing severe cortical turbidity(P<0.01). CONCLUSION: Long-term and low dose ionizing radiation exposure may increase the risk of ocular lens opacity, especially cortical and posterior subcapsular cataract, and affect the severity of the disease.

Thyroid nodule prevalence among women in areas of high natural background radiation, Karunagappally, Kerala, India.

PURPOSE: Radiation exposure has been reported to cause thyroid nodules. The study area was Karunagapally, which has several areas with high natural radiation levels derived from thorium and its decay products. Since thyroid abnormalities are more common in women, the focus was only on women. METHODS: The examinations included interview, ultrasonography of the thyroid and serum assays of free thyroxine (FT4), thyrotropin (TSH), and anti-thyroglobulin levels. Cumulative dose during the childhood and lifetime cumulative dose (lagged by 5 years) were estimated. RESULTS: We examined 524 female residents aged 17-73 years and found 75 cases of solitary solid thyroid nodules. The prevalence of thyroid nodules were 14.1 % (n = 42) in high dose panchayats and 14.5% (n = 33) in low-dose panchayats. In the logistic regression analysis adjusted for age, the prevalence of solitary thyroid nodule was not linearly related to childhood cumulative dose (P for trend = 0.159) and lifetime cumulative dose (P for trend = 0.333). The prevalence of thyroiditis and hypothyroidism was not related to natural radiation exposure. Serum levels of FT4 or TSH were not related to natural radiation exposure. CONCLUSIONS: The results obtained from the present study do not support the increase of solitary thyroid nodule, thyroiditis or hypothyroidism in relation to high-natural-background-radiation exposure.

Distribution of uranium, thorium and some stable trace and toxic elements in human hair and nails in Niska Banja Town, a high natural background radiation area of Serbia (Balkan Region, South-East Europe).

Human hair and nails can be considered as bio-indicators of the public exposure to certain natural radionuclides and other toxic metals over a long period of months or even years. The level of elements in hair and nails usually reflect their levels in other tissues of body. Niska Banja, a spa town located in southern Serbia, with locally high natural background radiation was selected for the study. To assess public exposure to the trace elements, hair and nail samples were collected and analyzed. The concentrations of uranium, thorium and some trace and toxic elements (Mn, Ni, Cu, Sr, Cd, and Cs) were determined using inductively coupled plasma mass spectrometry (ICP-MS). U and Th concentrations in hair varied from 0.0002 to 0.0771 µg/g and from 0.0002 to 0.0276 µg/g, respectively. The concentrations in nails varied from 0.0025 to 0.0447 µg/g and from 0.0023 to 0.0564 µg/g for U and Th, respectively. We found significant correlations between some elements in hair and nails. Also indications of spatial clustering of high values could be found. However, this phenomenon as well as the large variations in concentrations of heavy metals in hair and nail could not be explained. As hypotheses, we propose possible exposure pathways which may explain the findings, but the current data does not allow testing them.