Lecturer(probationary), Faculty of Medicine, University of Kelaniya
Effect of exposure to high background radiation on micronuclei frequency in lymphocytes in humans
Lanka Mineral Sands Ltd (LMS), has been mining mineral sands at Pulmoddai, Sri Lanka for almost six decades. It has been a major contributor for the Sri Lankan economy by export of the products. The mineral sands that are mined include monazite which contains thorium (Th). Th emits alpha particles on decay and gamma rays are emitted by the daughter products. Alpha particles and gamma rays are both hazardous to animals and humans. Exposure to alpha particles cause skin cancers and inhalation of duct particles that emit alpha particles cause lung cancers. Ingestion of monazite dust cause pancreatic cancers. Gamma rays are very penetrative and can damage an array of tissues in the body causing cancers on long term exposure even at very low doses. Employees of LMS and residents in the vicinity of the LMS have been exposed to these monazite sand mounds with out any measures of protection. Dosimetry is measurement of the radiation doses received and both physical dosimetry and biological dosimetry are used to asses the exposure levels. Biological dosimetry has been established as a sensitive method to estimate exposure to ionizing radiation by using different techniques and the cytokinesis blocked micronuclear (MN) assay is popular for large scale exposure studies as it is an easier, faster and reliable method. Peripheral blood lymphocyte MN frequency is the most popular of the MN assays. The objective of the study was to determine the frequency of MN among the persons residing in the vicinity of LMS and to determine the background radiation levels in the area. A cross sectional study was conducted from November 2012 to September 2016 among persons 35-45 years of age. Eligible persons were invited to participate after administering a screening questionnaire. A detailed questionnaire was used to gather sociodemographic data and other details. 10 ml of venous blood was drawn under aseptic conditions using disposable equipment by trained personnel after obtaining informed written consent. Culturing of lymphocytes, preparation of slides and scoring was done according to the International Atomic Energy Authority (IAEA) guidelines at the Faculty of Medicine, University of Kelaniya, Sri Lanka. Background radiation measurements were assessed using a portable dose meter and soil samples for gamma spectrometry were collected from residences of participants. Gamma spectrometry of the soil samples were done at the Atomic energy board of Sri Lanka.
Abstract: In India, High Background Radiation Areas (HBRAs) due to enhanced levels of naturally occurring radionuclides in soil (thorium and, to a lesser extent, uranium), are located along some parts of the coastal tracts viz. the coastal belt of Kerala, Tamilnadu and Odisha. It is conjectured that these deposits will result in higher emissions of radon isotopes ((222)Rn and (220)Rn) and their daughter products as compared to Normal Background Radiation Areas (NBRAs). While the annual external dose rates contributed by gamma radiations in these areas are about 5-10 times higher, the extent of increase in the inhalation dose rates attributable to (222)Rn and (220)Rn and their decay products is not well quantified. Towards this, systematic indoor surveys were conducted wherein simultaneous measurements of time integrated (222)Rn and (220)Rn gas and their decay product concentrations was carried out in around 800 houses in the HBRAs of Kerala and Odisha to estimate the inhalation doses. All gas measurements were carried out using pin-hole cup dosimeters while the progeny measurements were with samplers and systems based on the Direct radon/thoron Progeny sensors (DRPS/DTPS). To corroborate these passive measurements of decay products concentrations, active sampling was also carried out in a few houses. The results of the surveys provide a strong evidence to conclude that the inhalation doses due to (222)Rn and (220)Rn gas and their decay products in these HBRAs are in the same range as observed in the NBRAs in India.
Pub.: 13 Jun '15, Pinned: 06 Jul '17
Abstract: This study was conducted to investigate the influence of geological and soil formation on natural gamma (γ) radiation exposure. The aim of this study also to obtain a baseline data of γ radiation exposure and radioactivity associated with soil in the granitic territory at Western Region of Peninsular Malaysia. From 3727 in situ measurements of γ radiation dose rates, the mean value of dose rate obtained in this study is 204 nGy h−1 with the range of between 17 and 1039 nGy h−1. The mean value obtained in this study is three times higher than the world average value of 57 nGy h−1. Based on in situ measurements, the range of annual effective dose received by the population living in the study area is 0.02–1.28 mSv y−1. The study found that the levels of γ radiation exposures are strongly influenced by the geological and soil types. From the gamma spectrometry analysis, the mean radioactivity levels of 226Ra, 232Th and 40K in soil in western region Peninsular Malaysia are slightly higher and comparable with the places of “High Natural Background Radiation Areas” (HNBRAs) in the world as reported by UNSCEAR (2000). The mean value of 226Ra was 120 Bq kg−1 and ranged from 7 to 554 Bq kg−1, whilst for 232Th was 276 Bq kg−1 with a range of 23–1806 Bq kg−1. These values indicate 3 and 9 times, respectively, higher than the world average values. However, the radium equivalent activity (Raeq) obtained in this study (277 Bq kg−1) is lower than permissible values of 370 Bq kg−1. The radiological indices of radiation hazards in this study show that the index values are higher than the permissible limit values of 1. The mean value for gamma activity index (Iγ,) external hazard index (Hex), internal hazard index (Hin) was 1.89, 1.46 and 1.78, respectively. As well as γ radiation levels, radioactivity levels of 226Ra, 232Th and 40K also were strongly influenced by the geological and soil types.
Pub.: 11 Mar '16, Pinned: 06 Jul '17
Abstract: This work focuses on the radiometric characteristics of beach sand along the Hadhramout coast, Gulf of Aden, Yemen. Beach sands samples were collected from 27 locations. The activity concentrations of the terrestrial radionuclides 226Ra, 232Th, and 40K were determined. The results obtained provide pioneering data on the radioactivity levels in the coastal areas of Hadhramout. The radioactivity concentration of 232Th was found to be a major contributor to the enhanced level of radiation in some beaches. The radiological data were processed using one-way analysis of variance to find out the differences between the elevated and non-elevated 232Th groups of locations and multivariate statistical analysis, i.e., principal component analysis, discriminant analysis, and clustering analysis, to find similarities and correlation between the various samples and to discriminate between the two groups of locations. From the radiation hazard point of view, the outdoor annual effective dose for the region varied from 5.1 to 155.5 mSv with a mean value of 34.9 ± 31.9 mSv. The highest radiation level was found in Al-Jraf beach, where the highest absorbed dose rate of 126.8 nGyh−1 was recorded and the radiation hazard index exceeded twice the recommended limit of unity.
Pub.: 24 Jun '15, Pinned: 06 Jul '17
Abstract: There are many places on the earth, where natural background radiation exposures are elevated significantly above about 2.5 mSv/year. The studies of health effects on populations living in such places are crucially important for understanding the impact of low doses of ionizing radiation. This article critically reviews some recent representative literature that addresses the likelihood of radiation-induced cancer and early childhood death in regions with high natural background radiation. The comparative and Bayesian analysis of the published data shows that the linear no-threshold hypothesis does not likely explain the results of these recent studies, whereas they favor the model of threshold or hormesis. Neither cancers nor early childhood deaths positively correlate with dose rates in regions with elevated natural background radiation.
Pub.: 18 Dec '15, Pinned: 06 Jul '17
Abstract: A comprehensive study was carried out to determine the radioactivity concentration of soil samples from different sites of a high background radiation area in the eastern coast of India, Odisha state. The dose rate measuredin situvaried from 0.25 to 1.2 µSv h(-1) The gamma spectrometry measurements indicated Th series elements as the main contributors to the enhanced level of radiation and allowed the authors to find the mean level of the activity concentration (±SD) for(226)Ra,(228)Th and(40)K as 130±97, 1110±890 and 360±140 Bq kg(-1), respectively. Human exposure from radionuclides occurring outdoor was estimated based on the effective dose rate, which ranged from 0.14±0.02 to 2.15±0.26 mSv and was higher than the UNSCEAR annual worldwide average value 0.07 mSv. Additionally, X-ray fluorescence analysis provided information about the content of major elements in samples and indicated the significant amount of Ti (7.4±4.9 %) in soils.
Pub.: 31 Mar '16, Pinned: 06 Jul '17
Abstract: To study the effect of low-dose (rate) radiation on human health, we analyzed chromosomes of peripheral lymphocytes of residents in a high background radiation area (HBRA) and compared the results with those obtained from residents in a control area (CA) in Guangdong Province, China. Unstable types of chromosome aberrations (dicentrics and rings) were studied in 22 members of eight families in HBRA and 17 members of five families in CA. Each family consists of three generations. On average 2,600 cells per subject were analyzed. 27 adults and six children in HBRA and 25 adults and eight children in CA were studied with respect to translocations. On average 4,741 cells per subject were examined. We found an increase of the frequency of dicentrics and rings in HBRA, where the natural radiation level is three to five times higher than in the control area. But the increase of translocations in HBRA was within the range of individual variation in the controls.
Pub.: 27 May '04, Pinned: 06 Jul '17
Abstract: Radon ((222)Rn), thoron ((220)Rn) and their decay products may reach high levels in areas of high natural background radiation, with increased risk associated with mining areas. Historically, the focus has mostly been placed upon radon and progeny (RnP), but recently there have been reports of significant contributions to dose from thoron progeny (TnP). However, few direct measurements of TnP exist under outdoor conditions. Therefore, we assessed the outdoor activity concentrations of radon, thoron and TnP in an area of igneous bedrock with extreme levels of radionuclides in the thorium decay series. The area is characterized by decommissioned mines and waste rock deposits, which provide a large surface area for radon and thoron emanation and high porosity enhancing exhalation. Extreme levels of thorium and thoron have previously been reported from this area and to improve dose rate estimates we also measured TnP using filter sampling and time-integrating alpha track detectors. We found high to extreme levels of thoron and TnP and the associated dose rates relevant for inhalation were up to 8 μSvh(-1) at 100 cm height. Taking gamma irradiation and RnP into account, significant combined doses may result from occupancies in this area. This applies to recreational use of the area and especially previous and planned road-works, which in the worst case could involve doses as large as 23.4 mSv y(-1). However, radon and thoron levels were much more intense on a hot September day than during time-integrated measurements made the subsequent colder and wetter month, especially along the ground. This may be explained by cold air observed flowing out from inside the mines through a drainage pipe adjacent to the measurement stations. During warm periods, activity concentrations may therefore be due to both local exhalation from the ground and air ventilating from the mines. However, a substantially lower level of TnP was measured on the September day using filter sampling, as compared to what was measured with time-integrative alpha track detectors. A possible explanation could be reduced filter efficiency related to the attached progeny of some aerosol sizes, but a more likely cause is an upwards bias on TnP detectors associated with assumed deposition velocity, which may be different in outdoor conditions with wind or a larger fraction of unattached progeny. There is thus a need for better instrumentation when dealing with outdoor TnP.
Pub.: 24 May '16, Pinned: 06 Jul '17
Abstract: The studies of health effects in human populations living in places with high levels of natural background radiation are of crucial importance for understanding the impact of low doses of ionising radiation. The paper reviews some exemplary literature that addresses the likelihood of the radiation-;induced cancer in aforementioned regions. It is shown that using Bayesian analysis one can arrive at an essentially different conclusion concerning dose-;effect dependence from the one which could be guessed from first glance. The general conclusion is that cancers do not correlate with elevated radiation in regions with high natural background radiation.
Pub.: 29 Jan '16, Pinned: 06 Jul '17
Abstract: Abstract In order to identify radon-prone areas and evaluate radon risk level, a soil gas radon survey combined with gamma-ray spectrometry measurements was carried out in Shenzhen City, south China. Meanwhile, the statistical analysis was applied to evaluate the distribution of measured results. This paper presents the methodology of the radon risk assessment. A radon risk map was accomplished based on a combination of soil gas radon concentration (RC), soil air permeability (Perm.) and uranium (238U) concentration. The results showed that the distribution of soil gas RC and radon-prone areas were closely related to geologic distribution of uranium (238U) and local lithology.AbstractIn order to identify radon-prone areas and evaluate radon risk level, a soil gas radon survey combined with gamma-ray spectrometry measurements was carried out in Shenzhen City, south China. Meanwhile, the statistical analysis was applied to evaluate the distribution of measured results. This paper presents the methodology of the radon risk assessment. A radon risk map was accomplished based on a combination of soil gas radon concentration (RC), soil air permeability (Perm.) and uranium (238U) concentration. The results showed that the distribution of soil gas RC and radon-prone areas were closely related to geologic distribution of uranium (238U) and local lithology.238238
Pub.: 01 Sep '16, Pinned: 06 Jul '17
Abstract: Abstract Gamma spectral analysis for the presence of primordial radionuclides was done on the sediment samples collected from Tamiraparani River, Tamil Nadu, India, which originates in the Western Ghats and flows towards the eastern side of the high background radiation region of Southern Malabar Coast (Kerala). The average activity concentration values for the primordial radionuclides were observed to be higher than the world median ranges reported by UNSCEAR (Report to general assembly with scientific annexes, vol 1, Annex B. United Nations, New York, http://www.unscear.org/docs/publications/2008/UNSCEAR_2008_Annex-B-CORR.pdf, 2008). The radiological parameters calculated for river sediments were found to be comparatively higher than the recommended values. The computed correlation matrix exhibited a positive correlation between various geochemical parameters and the activity concentration values of the primordial radionuclides. The heavy mineral analysis also showed a noticeable correlation with the activity of the actinides. The solid-state electrical conductivity studies on the heavy mineral samples were investigated to study their correlation with the activity of the primordial radionuclides.AbstractGamma spectral analysis for the presence of primordial radionuclides was done on the sediment samples collected from Tamiraparani River, Tamil Nadu, India, which originates in the Western Ghats and flows towards the eastern side of the high background radiation region of Southern Malabar Coast (Kerala). The average activity concentration values for the primordial radionuclides were observed to be higher than the world median ranges reported by UNSCEAR (Report to general assembly with scientific annexes, vol 1, Annex B. United Nations, New York, http://www.unscear.org/docs/publications/2008/UNSCEAR_2008_Annex-B-CORR.pdf, 2008). The radiological parameters calculated for river sediments were found to be comparatively higher than the recommended values. The computed correlation matrix exhibited a positive correlation between various geochemical parameters and the activity concentration values of the primordial radionuclides. The heavy mineral analysis also showed a noticeable correlation with the activity of the actinides. The solid-state electrical conductivity studies on the heavy mineral samples were investigated to study their correlation with the activity of the primordial radionuclides.http://www.unscear.org/docs/publications/2008/UNSCEAR_2008_Annex-B-CORR.pdf2008
Pub.: 10 Jan '17, Pinned: 06 Jul '17
Abstract: In order to evaluate internal exposure to radon and thoron, concentrations for radon, thoron, and thoron progeny were measured for 259 dwellings located in high background radiation areas (HBRAs, outdoor external dose: 3-5 mGy y(-1)) and low background radiation areas (control areas, outdoor external dose: 1 mGy y(-1)) in Karunagappally Taluk, Kerala, India. The measurements were conducted using passive-type radon-thoron detectors and thoron progeny detectors over two six-month measurement periods from June 2010 to June 2011. The results showed no major differences in radon and thoron progeny concentrations between the HBRAs and the control areas. The geometric mean of the annual effective dose due to radon and thoron was calculated as 0.10 and 0.44 mSv, respectively. The doses were small, but not negligible compared with the external dose in the two areas.
Pub.: 22 Dec '16, Pinned: 06 Jul '17
Abstract: Thoron exhalation from earth’s surface is the most important source of environmental thoron. The High Background Radiation Areas (HBRAs) of Kerala and Odisha in India have beaches with sands enriched with monazite, an ore of thorium, making it unique for study of thoron exhalation. In the present study, in situ measurement of thoron exhalation was carried out to map the thoron exhalation rate over complete coastline of the known HBRAs. New experimental setups for measurement of thoron surface exhalation and thoron mass emanation were developed and validated. The exhalation measurements were carried out on beaches of Chavara–Neendakara (CN) area of Kerala and Chatrapur (CH) region of Odisha. The beaches of the Kerala region showed an average thoron exhalation rate of 5.95 ± 2.98 Bq m−2s−1, which for the beaches of Chatrapur area of Odisha was 2.77 ± 0.96 Bq m−2s−1. The external gamma exposure rate was also measured at these locations, and it was observed to be well correlated with in situ thoron exhalation rate. Sand samples were collected from ten of the measurement locations and analyzed in the laboratory for a further understanding of thoron exhalation process in the beach sand. Measurement of specific thoron mass emanation rate, specific 224Ra content and thoron emanation coefficient was taken for the samples. A good correlation was found between in situ thoron exhalation rate and specific thoron mass emanation rate. The effective thoron diffusion length was determined by using the measured parameters in the UNSCEAR radon exhalation model and was found to be nearly constant with a value of 2.2 ± 0.36 cm. This study shows that in spite of very high thorium content (500–1000 times) as compared to normal fine soils, the thoron exhalation from the HBRA beach sands was only 4–12 times higher due to very low emanation coefficient, about 1000 times smaller than that for normal soils.
Pub.: 25 Nov '16, Pinned: 06 Jul '17
Abstract: Twenty soil and 25 sediment samples were collected from the banks and bottom of the River Nile in the surroundings of biggest cities located close to it. Natural radioactivity concentrations of (226)Ra, (232)Th and (40)K have been evaluated for all samples by means of γ spectrometric analysis. The radioactivity levels of soil and sediment samples fall within the internationally recommended values. Nevertheless, high natural background radiation zones are detected in the Kafr El-Zayat region due to the presence of a fertilizer factory, and in the Rosetta region due to the presence of black sand deposits. The absorbed dose rate, the γ index and excess life time cancer risk are calculated. High values for some of the radiation health parameters are detected in the Kafr El-Zayat and Rosetta regions representing a serious problem to public health because the soil and sediment are used as constructing material for buildings. Furthermore, the isotope analysis of uranium for representative collected sediment samples via α spectrometry showed average specific activities of 18.7 ± 3.6, 0.087 ± 0.0038 and 18.6 ± 3.8 Bq kg(-1) for (234)U, (235)U and (238)U, respectively. In general, these values confirm the balance in the isotopic abundance of U isotopes.
Pub.: 14 Mar '17, Pinned: 06 Jul '17
Abstract: Genome stability is essential for normal foetal growth and development. To date, genome stability in human lymphocytes has not been studied in relation to late pregnancy diseases, such as pre-eclampsia (PE) and intrauterine growth restriction (IUGR), which can be life-threatening to mother and baby and together affect >10% of pregnancies. We performed a prospective cohort study investigating the association of maternal chromosomal damage in mid-pregnancy (20 weeks gestation) with pregnancy outcomes. Chromosome damage was measured using the cytokinesis-block micronucleus cytome (CBMNcyt) assay in peripheral blood lymphocytes. The odds ratio for PE and/or IUGR in a mixed cohort of low- and high-risk pregnancies (N = 136) and a cohort of only high-risk pregnancies (N = 91) was 15.97 (P = 0.001) and 17.85 (P = 0.007), respectively, if the frequency of lymphocytes with micronuclei (MN) at 20 weeks gestation was greater than the mean + 2 SDs of the cohort. These results suggest that the presence of lymphocyte MN is significantly increased in women who develop PE and/or IUGR before the clinical signs or symptoms appear relative to women with normal pregnancy outcomes. The CBMNcyt assay may provide a new approach for the early detection of women at risk of developing these late pregnancy diseases and for biomonitoring the efficacy of interventions to reduce DNA damage, which may in turn ameliorate pregnancy outcome.
Pub.: 29 Jun '10, Pinned: 01 Jul '17
Abstract: Over a century ago, Theodor Boveri paved the way to mechanistic studies linking chromosomal abnormalities to cancer pathogenesis. Since then, theoretical and empirical evidence has been accumulated, supporting a causal role of these events in the aetiology of human cancer. A powerful tool for measurement of chromosomal abnormalities is the cytokinesis-block micronucleus cytome (CBMNcyt) assay. The validation of the micronucleus (MN) as marker of phenotypic susceptibility to cancer has received decisive support from mutagens sensitivity studies, particularly from a recent case-control study on lung cancer, which showed increased frequency of tobacco carcinogen-induced MN, nuclear buds and especially nucleoplasmic bridges in cancer patients (odds ratios of 2.3, 10.0 and 45.5, respectively). Recently, a large international cohort study showed a significant association between MN frequency in healthy subjects and cancer risk. The study assembled data on 6718 individuals from 10 countries (62,980 person-years). Cancers incidence was significantly higher in groups with medium (RR=1.84; 95% confidence interval: 1.28-2.66) and high MN frequency (RR=1.53; 95% CI: 1.04-2.25). This study provided preliminary evidence that MN frequency in peripheral blood lymphocytes is predictive of cancer risk, suggesting that increased MN formation is associated with early events in carcinogenesis. These results, in combination with mechanistic evidence, prospected the use of MN frequency in cancer screening programmes. However, issues such as interindividual variability and preventive strategies in high-risk groups need to be further addressed to consolidate these achievements.
Pub.: 18 Dec '10, Pinned: 01 Jul '17
Abstract: Biological dosimetry, based on the analysis of micronuclei (MN) in the cytokinesis-block micronucleus (CBMN) assay can be used as an alternative method for scoring dicentric chromosomes in the field of radiation protection. Biological dosimetry or Biodosimetry, is mainly performed, in addition to physical dosimetry, with the aim of individual dose assessment. Many studies have shown that the number of radiation-induced MN is strongly correlated with dose and quality of radiation. The CBMN assay has become, in the last years, a thoroughly validated and standardised technique to evaluate in vivo radiation exposure of occupational, medical and accidentally exposed individuals. Compared to the gold standard, the dicentric assay, the CBMN assay has the important advantage of allowing economical, easy and quick analysis. The main disadvantage of the CBMN assay is related to the variable micronucleus (MN) background frequency, by which only in vivo exposures in excess of 0.2-0.3 Gy X-rays can be detected. In the last years, several improvements have been achieved, with the ultimate goals (i) of further increasing the sensitivity of the CBMN assay for low-dose detection by combining the assay with a fluorescence in situ hybridisation centromere staining technique, (ii) of increasing the specificity of the test for radiation by scoring nucleoplasmic bridges in binucleated cells and (iii) of making the assay optimally suitable for rapid automated analysis of a large number of samples, viz. in case of a large-scale radiation accident. The development of a combined automated MN-centromere scoring procedure remains a challenge for the future, as it will allow systematic biomonitoring of radiation workers exposed to low-dose radiation.
Pub.: 18 Dec '10, Pinned: 01 Jul '17