Public ingestion exposure to 226Ra in Ramsar, Iran.

Ramsar, in the north of Iran by the Caspian Sea, has been known for the highest natural radiation background on Earth due to the local geology and hydrogeology. The residents and visitors use the hot springs that distribute the natural radionuclides especially 226Ra and its decay products in the areas. Many studies have been undertaken to measure the absorbed dose rate in Ramsar's air, however, no survey has been done to assess public internal exposure from ingestion of natural radionuclides, such as, a broad survey for 226Ra was conducted in foodstuffs and drinking water. This study presents the results of public annual activity intake (Bq) and effective dose (µSv) from ingestion of 226Ra in foodstuffs and drinking water in Ramsar city. The total mean annual intake for adults was found to be 24.8 Bq. The annual average effective dose due to ingestion exposure to 226Ra was found to be 6.9 µSv for adults that were slightly more than the estimated global averages reported by UNSCEAR, 2000 (6.3 µSv). The contribution of drinking water and foodstuffs represent respectively about 30% and 70% of the total mean annual effective dose due to 226Ra. The highest effective dose from ingestion of 226Ra for adults was estimated to be 80.6 µSv y-1. Based on the results of this study, even with the largest 226Ra value in our survey, maximum annual effective dose due to consumption of foodstuffs and drinking water for children was 164.2 µ b Sv y-1.

ASSESSMENT OF TERRESTRIAL RADIATION BY DIRECT MEASUREMENT OF AMBIENT DOSE EQUIVALENT RATE OF BACKGROUND RADIATION.

Estimation of terrestrial external radiation is essential for assessment of public exposure to natural radiation. During national survey of natural radionuclide in soil in Iran, 979 soil samples were collected from different locations, in the same time ambient dose equivalent rate was measured by a scintillator detector. In this work, terrestrial radiation was estimated by direct measurement of ambient dose equivalent rate of background radiation. The response of dose measuring instrument to cosmic radiation at ground level was measured and other components were discussed and estimated. For verification, terrestrial radiation derived from this method was compared with those calculated from activity concentration of natural radionuclides in soil. The averages of ambient dose equivalent rate derived from activity concentration of by natural radionuclide in soil and from direct measurement are 55.07 and 62.57 nSv/h, respectively. The source of statistical and systematic uncertainties are introduced and discussed.

Prediction of dose to the relatives of patients treated with radioiodine-131 using neural networks.

In this study, the effective dose received by the family members and caregivers of 52 thyroid cancer patients, who had been treated with radioiodine I-131, was measured to investigate the ability of the neural network to predict the doses to the relatives. The effectiveness of this method to predict the relatives who will receive doses of more than 1 mSv was evaluated. The effective doses were measured by TLD. The inputs of the neural network include 13 different parameters that can potentially affect the dose, and the output was the dose to the family members. The neural networks in this study were feed-forward with a sigmoid activation function and one hidden layer. The mean and median of the measured doses were 0.45 and 0.28 mSv and its range was 0.1-3.64 mSv. The mean square error of the predicted doses by the neural network and the measured doses by TLD (mean squared error) for 99 individuals was 0.142. The optimum neural network was able to predict all the relatives who received doses of more than 1 mSv. The area under the receiver operating characteristic curve for the trained neural network was 0.957, showing its ability to distinguish these groups. Predicting the dose to a patient's relatives before release is a helpful strategy for future optimisation. Using neural networks is a promising method for predicting the dose to the family members and defining high-risk patients and relatives. Patient-specific criteria for release and patient-specific advice and consultation can be used to reduce the dose to each family member.

Radioactivity levels in the mostly local foodstuff consumed by residents of the high level natural radiation areas of Ramsar, Iran.

Among High Level Natural Radiation Areas (HLNRAs) all over the world, the northern coastal city of Ramsar has been considered enormously important. Many studies have measured environmental radioactivity in Ramsar, however, no survey has been undertaken to measure concentrations in the diets of residents. This study determined the 226Ra activity concentration in the daily diet of people of Ramsar. The samples were chosen from both normal and high level natural radiation areas and based on the daily consumption patterns of residents. About 150 different samples, which all are local and have the highest consumption, were collected during the four seasons. In these samples, after washing and drying and pretreatment, the radionuclide was determined by α-spectrometry. The mean radioactivity concentration of 226Ra ranged between 5 ± 1 mBq kg-1 wet weight (chino and meat) to 725 ± 480 mBq kg-1 for tea dry leaves. The 226Ra activity concentrations compared with the reference values of UNSCEAR appear to be higher in leafy vegetables, milk and meat product. Of the total daily dietary 226Ra exposure for adults in Ramsar, the largest percentage was from eggs. The residents consuming eggs from household chickens may receive an elevated dose in the diet.

Establishment of diagnostic reference levels for common multi-detector computed tomography examinations in Iran.

In order to establish diagnostic reference levels (DRLs) for multi-detector computed tomography (MDCT), four routine CT examinations were identified and a computer program was developed to collect data from 19 MDCT scanners in Iran. Mean values of Volume computed tomography dose index (CTDIvol) and dose-length product (DLP) in each site were calculated and the DRLs were defined as the 75th percentile of the distribution of the CTDIvol/DLP values for each examination. In terms of DLP, the DRLs of adult age group are 700, 290, 330, and 550 mGy cm for the Brain, Sinus, Chest, and Abdomen and Pelvis protocols, respectively. Although DRLs of this study are comparable to other international DRLs and in most cases are less than the international reference values, the great extent of dose distributions indicates that the CT imaging procedures in Iran should be optimized by applying diagnostic reference levels in order to decrease the radiation dose to patient undergoing CT examination.

Differential proteome analysis of a selected bacterial strain isolated from a high background radiation area in response to radium stress.

The present study describes the response of a bacterial strain, isolated from a hot spring in an area with the highest levels of natural radiation, under radium ((226)Ra) stress. The bacterium has been characterized as a novel and efficient radium biosorbent and identified as a variant of Serratia marcescens by biochemical tests and molecular recognition. In order to gain insights into key cellular events that allow this strain to survive and undergo (226)Ra adaptation and biosorption, the strain was tested under two experimental conditions of 1000 and 6000 Bq (226)Ra stress. A proteomic approach involving two-dimensional polyacrylamide gel electrophoresis and mass spectrometry was used to identify the differentially expressed proteins under (226)Ra stress. Functional assessment of identified proteins with significantly altered expression levels revealed several mechanisms thought to be involved in (226)Ra adaptation and conferring resistant phenotype to the isolate, including general stress adaptation, anti-oxidative stress, protein and nucleic acid synthesis, energy metabolism, efflux and transport proteins. It suggests that this strain through evolution is particularly well adapted to the high background radiation environment and could represent an alternative source to remove (226)Ra from such areas as well as industrial radionuclide polluted wastewaters.

Serratia sp. ZF03: an efficient radium biosorbent isolated from hot-spring waters in high background radiation areas.

The aim of this study is to isolate and characterize (226)Ra biosorbing indigenous bacterial strains from soils and hot-springs containing high concentrations of (226)Ra by using biochemical and molecular approaches. Fifteen bacteria were isolated and their phylogenetic affiliations were determined based on their 16S rRNA gene and the two most relevant hypervariable regions of this gene; V3 and V6 analysis. A pigmented Serratia sp. ZF03 strain isolated from the water with (226)Ra content of 50471 mBq l(-1), caused 70% removal of (226)Ra at a radioactivity level of 50 Bq ml(-1), after 5 min and 75-80% in equilibrium time of 1 h, depending on the particular biosorption system and experimental conditions studied. The biosorption equilibrium was described by Langmuir and Freundlich isotherm models. Kinetic studies indicated that the biosorption follows pseudo-second-order kinetics. Effect of different physico-chemical parameters on (226)Ra sorption, FTIR, SEM and TEM analysis were also investigated.