High Background Areas Research Articles

Microanalyses of uranium in Indian soil samples using solid state nuclear track detection technique

Uranium content of soil samples collected from different states of India, namely Uttar Prades, Rajasthan and Kerala has been estimated. The areas cover the normal background area, high background area and dumpyards of fertilizer factory and thermal power plant. Plastic sheets were used as a detector for the registration of fission tracks resulting from the (n, f) reaction on235U present in the sample due to the thermal neutrons from a nuclear reactor. The uranium concentration has been found to vary from 0.24 to 9.20 μg/g in various soil samples. Higher levels of uranium were found in the vicinity of a coal fired power plant. The present results may be useful for the radiation hygiene.

Determination of uranium in plants from high background area by instrumental neutron activation analysis

One of the most important problems related to the high background area is that of environmental contamination. Therefore a number of local plants from Kasar in Koprubasi as referred to high background area, West Anatolia, were investigated for their uranium contents as well as for other elements by using instrumental neutron activation analysis (INAA). All of the plants except wheat samples contained levels above 0.6 ppm U which is the average background concentration of uranium in the ashed samples of living plant material. Beside the uranium, the concentrations of the other trace elements such as Ce, Ba, Cr, La, Sc, Rb, Fe, Zn, Zr, Eu, Co, Cs, Br, As, Na, K, in the plant ashes were also determined.

Distribution of some natural and artificial radionuclides in Mangalore environment of South India

The activities of 40K, 226Ra, 228Ra, 210Po, 210Pb, 137Cs and 90Sr were determined in a number of natural samples in the environment of Mangalore, South India where large-scale industrial activities are envisaged. Well-established nuclear techniques were employed to measure the activities and wherever necessary radiochemical methods were also followed. The measurement of transfer coefficients indicated that the uptake of 226Ra, 228Ra and 210Pb in paddy is higher than that in vegetables. The measured activity ratios of 210Po: 210Pb and 228Ra: 226Ra in soil samples suggest the existence of equilibrium between the corresponding radionuclides in normal background areas and disequilibrium in high background areas. The intake of radionuclides by the population and the internal dose were estimated. The annual internal effective dose for the population is found to be 341 μSv year −1 which mainly arises from 40K and 210Pb.

Occurrence and infectivity of arbuscular mycorrhizal fungi in some norwegian soils influenced by heavy metals and soil properties

Mycorrhizae are ubiquitous symbiosis which can mediate uptake of some plant nutrients. In polluted soils they could be of great importance in heavy metal availability and toxicity to plants. Mycorrhizae have also been reported to protect plants against toxic metals. We investigated the occurrence and infectivity of arbuscular mycorrhizal (AM) spores as affected by heavy metal levels and other soil properties in Norwegian soils collected from heavy metal polluted, high natural background and non-polluted areas. Spore numbers, mycorrhizal infectivity and spore germination of indigenous mycorrhizal fungi and of a reference strain (Glomus mosseae) in soils showed lower values in two soils with high metal concentrations and in one soil with a low pH. Mycorrhizal infectivity was negatively correlated with extractable metals. Spore number and mycorrhizal infectivity in a soil with naturally high heavy metal content were not different to in non-polluted soils, and indigenous AM fungi appeared more tolerant to metals than those in non-polluted soils. Mycorrhizal infectivity, expressed as MSI50 values, was significantly correlated (r′=0.89, P< 0.05) with the percentage of germinating G. mosseae spores in the soils. However, the number of spores per volume of soil was not significantly correlated with infectivity or spore germination of the reference strain. The spore germination method is discussed as a bioassay of heavy metal toxicity in soil.

Distribution and Enrichment of Radionuclides in the Newly Discovered High Background Area in Ullal on the Southwest Coast of India

In order to understand the distribution of radionuclides in the newly discovered high background area in Ullal near Mangalore, soil and sand samples collected from different depths were analyzed for the concentration of primordial radionuclides by gamma spectrometry. The activity of 232Th and 238U in soil and sand was observed to be maximum in the 0-10 cm layer. The activity of primordial radionuclides was determined for the different size fractions of soil and sand to study the enrichment pattern. The highest activity was found in the 250-125 mu fraction in both soil and sand. The concentration of primordial radionuclides in riverine and marine sediments in the vicinity of the high background area was measured to understand the transportation of radionuclides in riverine and marine environments and to throw light on the formation of the new patches of monazite deposit. The results of these systematic investigations are discussed in this paper.

Thoron Exposure of Man: A Negligible Issue?

Abstract The existing database on thoron (Tn) in the environment, the experimental validation of dosimetric models and potential health effects are scarce. Available information on Tn and its decay products (Tn-d) indoors and outdoors is associated with partly significant uncertainties due to methodological shortcomings. Dosimetric modelling reveals that ThB (212Pb) data are to be considered as the most important input parameter. Under typical indoor exposure conditions the dose due to Tn-d is about one order of magnitude less than from radon decay products (Rn-d). However, special circumstances have been identified where the Tn-dose contribution can exceed the corresponding Rn-d values. Several health effects have been associated with elevated exposure among workers in thoron-related industries and residents in high thoron background areas.

External gamma radiation dose rates in coastal Karnataka

External gamma-ray dose rates in air have been measured using a sensitive plastic scintillometer in the environment of coastal Karnataka, on the south west coast of India, where intensive industrial activities including a nuclear power plant, a super thermal power station and a petrochemical complex are envisaged. The gamma dose rates in air range from 26 to 174 nGy h-1 with a geometric mean of 74 nGy h-1 and geometric standard deviation of 1.4. The activity of primordial radionuclides in soil samples of the region were measured using an HPGe gamma ray spectrometer and the resulting doses in air were calculated. The mean absorbed dose rate due to primordial radionuclides was 41.4 nGy h-1 with a geometric standard deviation of 1.4. A correlation was found between doses measured using scintillometer and doses estimated from the measured activity of primordial radionuclides when the cosmic ray component is taken into account. The concentration of primordial radionuclides in soil and sand show considerable variation in their vertical depth distribution in the high background area of the region.

Radiation exposure at the high background area at Manavalakurichi — The changing trends

Large-scale surface mining and refilling of the mined areas with monazite-free tailings have reduced the external radiation fields by an order of magnitude, at some locations at the natural high background areas situated in the coastal regions of peninsular India. Significant reduction by a factor of 3 has been observed in the airborne activity due to lower emanation of thoron (220Rn) at the refilled areas. The thathched huts in the area are giving way to brick and concrete structures, thus radically altering the indoor exposures. The exposure due to gamma radiation from the external surroundings was reduced by a factor of 4 due to the shielding by the construction materials. 220 Rn levels as high as 420 Bq m −3 have been observed in some of the mud houses. Significant levels of 232 Th and 228 Ra were found in the urine samples collected from the adult residing in a village, situated in the high background area.

A New Natural Background Radiation Area on the Southwest Coast of India

The systematic study of background radiation and the distribution of radionuclides in the environment of coastal Karnataka, South India, has been initiated with an objective of establishing reliable baseline data on the background radiation level of the region for future assessment of the impact of nuclear and thermal power stations that are being set up in the region. The ambient gamma radiation survey in the environment of Mangalore, a major industrial city of coastal Karnataka, revealed significantly high gamma dose in air in certain locations of the Mangalore beach area. Thermoluminescent dosimetric studies indicated conspicuously high gamma dose in air in these places. Gamma spectrometric analyses of the soil and sand samples of this high background area have been carried out. The measured gamma dose in air in high background area is in the range 44-2102 nGy h-1. The average activity of 232Th, 238U, and 40K in soil samples is 2,971 Bq kg-1, 546 Bq kg-1, and 268 Bq kg-1, respectively. In sand samples, the respective activities are 1,842 Bq kg-1, 374 Bq kg-1, and 158 Bq kg-1. Results of these systematic investigations which establish the existence of new patches of monazite in the Mangalore beach area, on the southwest coast of India, are presented in this paper.

Simultaneous determination of232Th and238U in biological samples. Application to the estimation of their daily intake through diet

A simple method employing neutron activation and radiochemical separation was developed for simultaneous determination of the concentrations of232Th(Th) and238U(U) in biological materials. Using this method, it is possible to detect 0.05 and 0.2 ng of Th and U, respectively, in the samples. This method was applied to determine the daily dietary intake of these two nuclides by the population living in the high background areas of India (Monazite area), where the soil contains very high levels of these two nuclides. The comparison of the daily intakes by the population living in high and normal background areas showed significantly higher intake of these two nuclides by the high background population.

Thyroid Nodularity and Chromosome Aberrations Among Women in Areas of High Background Radiation in China

Thyroid nodularity following continuous low-dose radiation exposure in China was determined in 1,001 women aged 50-65 years who resided in areas of high background radiation (330 mR/yr) their entire lives, and in 1,005 comparison subjects exposed to normal levels of radiation (114 mR/yr). Cumulative doses to the thyroid were estimated to be of the order of 14 cGy and 5 cGy, respectively. Personal interviews and physical examinations were conducted, and measurements were made of serum thyroid hormone levels, urinary iodine concentrations, and chromosome aberrations in circulating lymphocytes. For all nodular disease, the prevalences in the high background and control areas were 9.5% and 9.3%, respectively. For single nodules, the prevalences were 7.4% in the high background area and 6.6% in the control area (prevalence ratio = 1.13; 95% confidence interval = 0.82-1.55). There were no differences found in serum levels of thyroid hormones. Women in the high background region, however, had significantly lower concentrations of urinary iodine and significantly higher frequencies of stable and unstable chromosome aberrations. Increased intake of allium vegetables such as garlic and onions was associated with a decreased risk of nodular disease, which seems consistent with experimental studies suggesting that allium compounds can inhibit tumor growth and proliferation. The prevalence of mild diffuse goiter was higher in the high background radiation region, perhaps related to a low dietary intake of iodine. These data suggest that continuous exposure to low-level radiation throughout life is unlikely to appreciably increase the risk of thyroid cancer. However, such exposure may cause chromosomal damage.

Indoor Levels of Radon Daughters in Some High Background Areas in India

In view of the recent recognition the world over the importance of assessing the levels of radon concentration present in the indoor environments of human dwellings, we have started a programme to measure the indoor radon and daughter concentrations in Indian houses. As a part of the project, we have made measurements of indoor Rn in houses located in the so-called high background areas. The present measurements have given a geometric mean of 9.4 mWL of potential alpha energy exposure level from Rn daughters, which corresponds to an annual effective dose equivalent of 3.1 mSv.

Contribution to the Study of Portuguese Population Exposure to Gamma Radiation

Abstract The initiation and development of a programme of surveying gamma radiation in Portugal is reported. Outdoor measurements of gamma radiation levels were carried out all over the country, contributing first estimates towards the establishment of a radiological map. Three specific regions were studied in more detail. One of them is well known as a high background area where uranium mines are in operation and the other two are related to sites selected for the installation of nuclear power plants. Indoor measurements in dwellings were made in two specific areas, Distrito de Viseu and Distrito de Braganca, respectively, of high and medium radiation levels. These values are insufficient to give a complete picture of the population exposure but they give an overview of the average dose rates in the country and an estimate of the average population doses for two particular regions.

Determination of plutonium and americium in environmental samples and assessment of thorium in bone samples from normal and high background areas

The procedures developed and standardised for estimation of ultra trace quantities of Pu and Am in environmental samples involve matrix dependent sample preparation, preconcentration of the nuclides by coprecipitation on iron hydroxide and or bismuth phosphate, ion exchange, electrodeposition and counting by alpha spectrometry. Isotopic analysis of Th in chicken bone using oxalate precipitation, ion exchange, electrodeposition and alpha spectrometry has indicated higher build up of228Th in chicken bone from monazite areas possibly from metabolized228Ra.

Lung cancer incidence in a Chinese high background area — Epidemiological results and theoretical interpretation

Lung cancer incidence in a Chinese high background area — Epidemiological results and theoretical interpretation

Lung cancer risk at low doses of alpha particles.

A survey of inhabitant exposures arising from the inhalation of 222Rn and 220Rn progeny, and lung cancer mortality has been carried out in two adjacent areas in Guangdong Province, People's Republic of China, designated as the "high background" and the "control" area. Annual exposure rates are 0.38 working level months (WLM) per year in the high background, and 0.16 WLM/yr in the control area. In 14 yr of continuous study, from 1970 to 1983, age-adjusted mortality rates were found to be 2.7 per 10(5) living persons of all ages in the high background area, and 2.9 per 10(5) living persons in the control area. From this data, we conclude that we are unable to determine excess lung cancers over the normal fluctuations below a cumulative exposure of 15 WLM. This conclusion is supported by lung cancer mortality data from Austrian and Finnish high-background areas. A theoretical analysis of epidemiological data on human lung cancer incidence from inhaled 222Rn and 220Rn progeny, which takes into account cell killing as competitive with malignant transformation, leads to the evaluation of a risk factor which is either a linear-exponential or a quadratic-exponential function of the alpha-particle dose. Animal lung cancer data and theoretical considerations can be supplied to support either hypothesis. Thus we conclude that at our current stage of knowledge both the linear-exponential and the quadratic-exponential extrapolation to low doses seem to be equally acceptable for Rn-induced lung cancer risk, possibly suggesting a linear-quadratic transformation function with an exponential cell-killing term, or the influence of risk-modifying factors such as repair or proliferation stimuli.

Measurement of radon and thoron present in the environment using nuclear track etch detector technique

Abstract The use of solid state nuclear tract detectors (SSNTD) is one of the most convenient techniques to assess the average radiation levels of alpha activities in the environment. This technique has been used to assess the radon and thoron concentrations in some high background areas of South India and underground non-uranium mines in Bihar State. Exposed SSNTD films are chemically etched in an alkali solution and the alpha tracks are evaluated under an optical microscope. The detailed procedure for this study and the calibration of the etched films for conversion of alpha track density to radon and thoron concentrations in pCi l-1 are given in this paper. It was found that 1.9 tracks cm-2 day-1 and 6.2 tracks cm-2 day-1 were produced by exposing the LR-115 foils to 1 pCi l-1 of thoron and radon respectively.

Lung cancer incidence in a Chinese high background area — Epidemiological results and theoretical interpretation

A survey of inhabitant exposures arising from the inhalation of radon and thoron daughters, and lung cancer mortality has been carried out in two adjacent areas in Guangdong province, China, designated as the “high background” and the “control” area. Annual exposure rates are 0.38 WLM/yr in the high background, and 0.16 WLM/yr in the control area, while age-adjusted mortality rates are 2.7 per 10 5 living people of all ages in the high background, and 2.9 per 10 5 in the control area. From this data we conclude that we are unable to determine the excess lung cancer rate over normal fluctuations below a cumulative exposure of about 15 WLM. This conclusion is supported by lung cancer mortality data from an Austrian high background area.

Radiation exposures and risks due to airtightening of homes in an alpine area with high radon emanation

Radon and its short-lived decay products in the indoor environment are the most important single source of exposure to ionizing radiation in Switzerland. Modifications in the construction of dwellings implemented to reduce energy consumption may change indoor pollutant levels and cause substantial long term hazards to the general public (1). The following estimate of additional exposure of humans to the ionizing radiation from radon and its short-lived progeny in the indoor air of energy efficient dwellings, i.e. homes showing low air exchange rates, is based on radon measurements in Swiss alpine regions with high terrestrial radiation. Differences in the indoor radon levels between new or retrofitted dwellings are derived from a matched pair study of single family homes in Switzerland (2). Risk factors for lung cancer induction from radon exposure have to rely mostly on occupational exposures in mines. However, the integral dose over the human life span from radon and its progeny in the indoor air in high background areas may approach or even exceed the values of miner populations showing significant increases in the incidence of malignant lung diseases. Although confounding factors such as poor control of smoking habits and additional chemihal toxicants in mine air do not permit a direct comparison of environmental and occupational exposure risks, both radiobiological considerations and the results from human epidemiology point to a linear dose effect relationship. This is in clear contrast to the case of formaldehyde, where no human data exist and where nasal carcinomas in rats follow a non-linear dose-effect relationship.

Environmental radioactivity and thermoluminescence: A review

A close link exists between environmental radioactivity and thermoluminescence (TL) and this connection can be gainfully employed in (i) environmental radiation surveillance, (ii) radioactive prospecting and (iii) dating. The science of thermoluminescence dosimetry (TLD) is very well established for use in routine radiation monitoring. With the increased public awareness of health effects due to radioactivity releases from nuclear operations. TLDs have become indispensible ‘watchdogs’ in environmental surveillance; in high natural background areas such as the monazite regions, TLDs have yielded invaluable dosimetric data. Over large areas where the cosmic background can be assumed constant, the TLD-recorded radiation profiles can reflected the terrestrial gamma radioactivity distribution pattern and even seasonal variations in the radiation levels above ground may be delineated. A variety of natural materials like minerals, rocks, soils, sands, sediments, fossils, etc., as well as ancient artefacts like potteries and ceramic wares, yield TL even without any irradiation in the laboratory: the natural radioactivity in these materials, together with the radiation incident on them from the environment, causes a TL build-up during antiquity. It is possible to measure this natural TL and relate it to the natural radioactivity of the sample and hence to its age. In contrast, observations of a kind of anticorrelation between TL and a sample's radioactivity have also been made in recent times and the effect is mostly ascribable to alpha-radioactivity-induced damage effects. Typical results from recent investigations of the various aspects mentioned above are presented in this review, with particular emphasis on applications in India.