Dose measurement, its distribution and individual external dose assessments of inhabitants in the high background radiation areas in China

Radioactivity and elemental oxidation composition in soil from Yangjiang, a high background natural radiation area, China

Soil is an important source and medium of radionuclides, and the content of radioactivity in soil is crucial for radiological impact evaluation. In this study, twenty soil samples in the high background natural radiation area of Yangjiang, China were collected and analyzed for 226Ra, 232Th, 40K and 137Cs concentrations in order to evaluate the radiological health risk in the area. Results showed that the average activity concentrations of 226Ra, 232Th and 40K are 66 Bq/kg, 109 Bq/kg and 211 Bq/kg, respectively. The calculated radiological parameters of radium equivalent activity (Raeq), absorbed dose rate (D), annual effective dose equivalent (AEDE), internal and external hazard indices (Hin and Hex) show a large variation at different sampling sites. Additionally, the elemental oxidation composition and 40K/K mass ratio in the soil were analyzed to further augment the background information of the high background radiation area in Yangjiang.

Assessment of radiation hazard indices due to naturally occurring long-life radionuclides in the coastal area of Barra de Valizas, Uruguay

The Uruguayan east coast has several mineral resources, which include black sand ores in the Barra de Valizas-Aguas Dulces area. Cancer in Uruguay shows non-homogeneous geographical distribution, with the highest standardized mortality ratio (SMR) in the northeast and east region, which includes the aforementioned area and the town of Barra de Valizas. The activity concentration of natural radionuclides (226Ra, 232Th and 40 K) in Barra de Valizas´soil was determined by gamma spectrometry in order to evaluate the radiological hazard for inhabitants and tourists. The outdoor annual effective dose (AEDE), excess lifetime cancer risk (ELCR), and annual gonadal dose equivalent (AGDE) were evaluated for inhabitants with a life expectancy of 77.7 years, a 0.2 and 0.5 occupancy factor, and using the conversion coefficients recommended by United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). The annual effective dose was also evaluated for both summer and fortnight tourists. The radiological hazard indices for Barra de Valizas inhabitants are higher than the worldwide mean and recommended values. This may contribute to Rocha's higher SRM value, although a direct correlation cannot be assured with the epidemiological information currently available. Social, medical and anthropological studies will be carried out in future to provide data and verify this correlation.

Lens opacity prevalence among the residents in high natural background radiation area in Yangjiang, China

The aim of the study was to evaluate the risk and threshold doses of lens opacity among residents exposed to low-dose radiation. Residents aged ≥45 years were recruited from a high natural background radiation (HNBR) area in Yangjiang City and a control area selected from nearby Enping City. Lens opacities (LOPs) were classified according to the Lens Opacities Classification System (LOCS) III system. Face-to-face interviews were conducted to collect information on lifestyles, migration and medical history. Life-time cumulative doses were estimated using gender, age, occupancy factors and environmental radiation doses received indoors and outdoors. Logistic regression analyses were conducted to estimate the dose response and determine thresholds. In the HNBR area, among 479 study participants, 101 (21.1%), 245(51.1%) and 23 cases (4.8%), respectively, of cortical, nuclear and posterior subcapsular (PSC) LOPs were found. In the control area, those types of LOPs were identified among 58 cases (12.6%), 206 cases (51.2%) and 6 cases (1.3%) of 462 examinees, respectively. Cumulative eye lens dose was estimated to be 189.5 ± 36.5 mGy in the HNBR area. Logistic analyses gave odds ratios at 100 mGy of 1.26 [95% confidence interval (CI) 1.00-1.60], 0.81 (95% CI 0.64-1.01) and 1.73 (95% CI 1.05-2.85) for cortical, nuclear and PSC LOPs, respectively. For cortical LOPs, a logistic analysis with a threshold dose gave a threshold estimate of 140 mGy (90% CI 110-160 mGy). The results indicated that population exposed to life-time, low-dose-rate environmental radiation was at an elevated risk of cortical and PSC LOPs. A statistically significant threshold dose was obtained for cortical LOPs and no threshold dose for PSC LOPs.

Strengths and Weaknesses of Dosimetry Used in Studies of Low-Dose Radiation Exposure and Cancer

BACKGROUND

A monograph systematically evaluating recent evidence on the dose-response relationship between low-dose ionizing radiation exposure and cancer risk required a critical appraisal of dosimetry methods in 26 potentially informative studies.

METHODS

The relevant literature included studies published in 2006-2017. Studies comprised case-control and cohort designs examining populations predominantly exposed to sparsely ionizing radiation, mostly from external sources, resulting in average doses of no more than 100 mGy. At least two dosimetrists reviewed each study and appraised the strengths and weaknesses of the dosimetry systems used, including assessment of sources and effects of dose estimation error. An overarching concern was whether dose error might cause the spurious appearance of a dose-response where none was present.

RESULTS

The review included 8 environmental, 4 medical, and 14 occupational studies that varied in properties relative to evaluation criteria. Treatment of dose estimation error also varied among studies, although few conducted a comprehensive evaluation. Six studies appeared to have known or suspected biases in dose estimates. The potential for these biases to cause a spurious dose-response association was constrained to three case-control studies that relied extensively on information gathered in interviews conducted after case ascertainment.

CONCLUSIONS

The potential for spurious dose-response associations from dose information appeared limited to case-control studies vulnerable to recall errors that may be differential by case status. Otherwise, risk estimates appeared reasonably free of a substantial bias from dose estimation error. Future studies would benefit from a comprehensive evaluation of dose estimation errors, including methods accounting for their potential effects on dose-response associations.

Gamma dose rate distribution in the Unegt subbasin, a uranium deposit area in Dornogobi Province, southeastern Mongolia

Unegt subbasin in Dornogobi Province, southeastern Mongolia, contains the Dulaan Uul uranium deposit, for which development for commercial mining has been conducted as of 2015. Zuunbayan is a commune located close to the Dulaan Uul uranium deposit, and residents of Zuunbayan and their livestock can easily approach the uranium deposit area, including an aboveground dump site, which was created as a result of the mining development. The present study measured and analyzed the gamma dose rate (absorbed dose rate in air) distribution in Unegt subbasin using data collected from a car-borne measurement survey. The gamma dose rate increased from the northern (45-65 nGy/h) to the central (50-69 nGy/h, including Zuunbayan) and the southern (54-195 nGy/h, including Dulaan Uul) parts of the study area. The gamma dose rates (up to 195 nGy/h) around the dump site in Dulaan Uul were significantly higher than the background level (< 80 nGy/h) at several points. Additional in-situ measurements showed that the gamma dose rates reached up to 450 nGy/h at these locations, which was primarily attributed to the gamma radiation emitted by ²³⁸U series elements. Spatial distribution of gamma dose rates around the dump site revealed that the gamma radiation did not originate from the dump, but from the ground, at the measurement points. Analysis of collected soil samples showed that ²³⁸U and ²²⁶Ra were concentrated in deeper soil. These results indicate that the gamma dose rates higher than the background level were not associated with the aboveground mine dump; rather, they were very probably caused by presence of uranium deposits close to the ground surface.

Typical doses and dose rates in studies pertinent to radiation risk inference at low doses and low dose rates

In order to quantify radiation risks at exposure scenarios relevant for radiation protection, often extrapolation of data obtained at high doses and high dose rates down to low doses and low dose rates is needed. Task Group TG91 on 'Radiation Risk Inference at Low-dose and Low-dose Rate Exposure for Radiological Protection Purposes' of the International Commission on Radiological Protection is currently reviewing the relevant cellular, animal and human studies that could be used for that purpose. This paper provides an overview of dose rates and doses typically used or present in those studies, and compares them with doses and dose rates typical of those received by the A-bomb survivors in Japan.

Radiation survey on Fukushima Medical University premises about four years after the Fukushima nuclear disaster

This study was conducted on the Fukushima Medical University (FMU) premises (in Fukushima City, Fukushima Prefecture) about four years after the Fukushima Daiichi Nuclear Power Plant accident.　Its objectives were (1) to create a map of the ambient gamma dose rate (air-kerma rate) distribution, (2) to evaluate the air-kerma rate originating from natural radionuclides, and (3) to investigate the effects of snow cover on changes in the air-kerma rate.　This man-borne survey revealed that the air-kerma rate varies widely, ranging from 0.038 μGy h(－1) to 0.520 μGy h(－1), and is higher on grass than on the other investigated surface types, such as soil, asphalt, and bricks.　In this area, the mean air-kerma rate from natural radiation was evaluated to be 0.03 ± 0.01 μGy h(－1), which is close to 0.04 μGy h(－1), which was measured in central Fukushima City by a local authority.Furthermore, snowfall was found to reduce the air-kerma rate by 5%-30%.　This reduction was attributed to attenuation of the primary radiation while passing through the snow cover, and the measured contribution of scattered radiation to the air-kerma rate reduction was small.　The reduction rate was found to depend on the initial snow depth but to maintain a similar value for a couple of days, after the snow had partially melted and its depth had decreased.　Finally, analysis of the daily dose due to external exposure received on the FMU premises revealed that no further health effects due to chronic radiation exposure at this site are to be expected.

Cancer and non-cancer mortality among Inhabitants in the high background radiation area of Yangjiang, China (1979-1998)

The present study aimed to evaluate the effects of high background radiation (HBR) on mortality. A cohort of 31,604 men and women aged 30-74 y living in the study area in Guangdong Province, China, was followed during the period 1979-1998. The information on deaths and migrations of cohort members was collected by visiting study areas every 3-4 y. Cumulative external radiation dose, lagged by 2 y for leukemia and 10 y for cancer excluding leukemia, was estimated for each individual based on hamlet-specific indoor and outdoor doses, and gender- and age-specific house occupancy factors. The follow-up study accumulated 736,942 person-years at risk and ascertained 6,005 deaths, including 956 cancer deaths and 4,525 non-cancer disease deaths. Mean cumulative radiation doses from natural radiation in the HBR and control area residents were 84.8 mGy and 21.6 mGy, respectively. Mortality due to leukemia (15 deaths) or cancer excluding leukemia (941 deaths) was not related to cumulative radiation dose. The excess relative risk (ERR) Gy of cancer excluding leukemia was estimated to be -1.01 (95% CI: -2.53, 0.95). In site-specific analysis, liver-cancer mortality was inversely related to the cumulative dose (p=0.002). Note, however, that liver cancer is well known for its difficulty in accurate diagnosis. The ERR Gy of cancer excluding leukemia and liver cancer was 0.19 (95% CI: -1.87, 3.04). Non-cancer disease mortality was not related to cumulative radiation dose either. The cumulative HBR dose was not related to the mortality due to cancer or all non-cancer diseases among residents in Yangjiang HBR areas.

An introductory overview of the epidemiological study on the population at the high background radiation areas in Yangjiang, China

The epidemiological study on the residents of the high background radiation areas in Yangjiang, China was started by Chinese scientists in 1972 and continued until 1986. In 1991, Japanese scientists recognized the importance of the work and a joint feasibility study was conducted with revised protocols. The feasibility study matured to a cooperative project involving both Chinese and Japanese scientists in 1992, which currently is still in progress. The project was divided into three phases; the first being from 1992 to 1995, the second from 1995-1998 and the third from 1998 to 2001. The results of the first phase were reported previously in 1996. The present paper is a historical overview of the studies before the cooperation and the first two phases. Remarks are made on the detailed data on dosimetry, cytogenetic studies and cancer epidemiology of a series of the papers in this supplemental issue. Some problems such as paradoxical observations between cytogenetic results and cancer mortality, and the importance of the high background study in risk assessment are discussed.