Chemical, radiological and microbiological characterization of a drinking water source: a case study.

This study examined water samples from a local stream in Central Serbia, which was consumed as drinking water. The chemical parameters (chemical oxygen demand, COD; pH, total concentration of dissolved substances and electrical conductivity), the concentration of major, trace and radioactive elements in the water as well as the content of those from the environment, were examined. In addition, the microbiological quality of the water was inspected. The water samples were acidic (pH from 5·27-5·69) and COD ranged in upper permissible limits (up to 6·25 mg O2 l-1 [WR]). The concentrations of major, trace and radioactive elements, including radon, were below maximum contaminant levels. The water contained a higher number of total coliform bacteria (TCB) than it was allowed (˃10 colony-forming units (CFU) in 100 ml of water) as well as enterococci and Escherichia coli. The characterization of the isolated bacteria indicated that two isolates demonstrated proteolytic activity, while full antibiotic resistance was not detected. The isolates showed moderate to strong ability to produce biofilm, while the isolates of E. coli were nonpathogenic. The results indicated that examined water samples were not microbiologically and chemically safe, therefore, the usage of analysed water was not recommended as a water supply. Further research needs to include more frequent monitoring in order to propose measures for the improvement of the water quality and prevention of health risks for consumers.

Exposure of school children to polycyclic aromatic hydrocarbons, heavy metals and radionuclides in the urban soil of Kragujevac city, Central Serbia.

The concentrations of radionuclides, polycyclic aromatic hydrocarbons (PAHs) and heavy metals were measured in soil samples collected from school backyards and playgrounds in Kragujevac, one of the largest cities of Central Serbia. The activity concentrations of (226)Ra, (232)Th, (40)K and (137)Cs were determined using the HPGe semiconductor detector. The average values were 34.6, 44.7, 428.9 and 45.1 Bq kg(-1), respectively. The correlation between the activity concentrations of (226)Ra in the soil samples and the results of the previous measurement of (222)Rn concentrations in the indoor air was examined. The absorbed dose rates, the annual effective doses and excess lifetime cancer risk were also estimated. The activity concentrations of (226)Ra and (232)Th have shown normal distribution. The collected soil samples were analysed for PAHs by HPLC. All analysed soil samples contained PAHs, and their total amounts (for 15 measured compounds) were found to be between 0.038 and 3.136 mg kg(-1) of absolutely dry soil (a.d.s). In addition the concentrations of As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn were measured in the fourteen soil samples collected from the playgrounds of kindergartens.

Radioactivity levels and heavy metals in the urban soil of Central Serbia.

Radioactivity concentrations and heavy metal content were measured in soil samples collected from the area of Kragujevac, one of the largest cities in Serbia. The specific activities of (226)Ra, (232)Th, (40)K and (137)Cs in 30 samples were measured by gamma spectrometry using an HPGe semiconductor detector. The average values ± standard deviations were 33.5 ± 8.2, 50.3 ± 10.6, 425.8 ± 75.7 and 40.2 ± 26.3 Bq kg(-1), respectively. The activity concentrations of (226)Ra, (232)Th and (137)Cs have shown normal distribution. The annual effective doses, radium equivalent activities, external hazard indexes and excess lifetime cancer risk were also estimated. A RAD7 device was used for measuring radon exhalation rates from several samples with highest content of (226)Ra. The concentrations of As, Co, Cr, Cu, Mn, Ni, Pb and Zn were measured, as well as their EDTA extractable concentrations. Wide ranges of values were obtained, especially for Cr, Mn, Ni, Pb and Zn. The absence of normal distribution indicates anthropogenic origin of Cr, Ni, Pb and Zn. Correlations between radionuclide activities, heavy metal contents and physicochemical properties of analysed soil were determined by Spearman correlation coefficient. Strong positive correlation between (226)Ra and (232)Th was found.

The accuracy of radon and thoron progeny concentrations measured through air filtration.

The accuracy and the optimization of determining radon and thoron progeny concentrations in air using air filtration followed by alpha activity measurements were investigated in details. The effects of radon and thoron concentrations, filtering duration and the choice of measuring intervals on relative standard deviations were analyzed. Obtaining satisfactory results by this method should be expected only in the case of high radon and thoron progeny concentrations in air. The optimization process also showed up to be dependent on the progeny concentration. Determinant of the system matrix and its effect on the sensitivity of the results were investigated.

Analysis of radon and thoron progeny measurements based on air filtration.

Measuring of radon and thoron progeny concentrations in air, based on air filtration, was analysed in order to assess the reliability of the method. Changes of radon and thoron progeny activities on the filter during and after air sampling were investigated. Simulation experiments were performed involving realistic measuring parameters. The sensitivity of results (radon and thoron concentrations in air) to the variations of alpha counting in three and five intervals was studied. The concentration of (218)Po showed up to be the most sensitive to these changes, as was expected because of its short half-life. The well-known method for measuring of progeny concentrations based on air filtration is rather unreliable and obtaining unrealistic or incorrect results appears to be quite possible. A simple method for quick estimation of radon potential alpha energy concentration (PAEC), based on measurements of alpha activity in a saturation regime, was proposed. Thoron PAEC can be determined from the saturation activity on the filter, through beta or alpha measurements.

Computer program for the sensitivity calculation of a CR-39 detector in a diffusion chamber for radon measurements.

Computer software for calculation of the sensitivity of a CR-39 detector closed in a diffusion chamber to radon is described in this work. The software consists of two programs, both written in the standard Fortran 90 programming language. The physical background and a numerical example are given. Presented software is intended for numerous researches in radon measurement community. Previously published computer programs TRACK_TEST.F90 and TRACK_VISION.F90 [D. Nikezic and K. N. Yu, Comput. Phys. Commun. 174, 160 (2006); D. Nikezic and K. N. Yu, Comput. Phys. Commun. 178, 591 (2008)] are used here as subroutines to calculate the track parameters and to determine whether the track is visible or not, based on the incident angle, impact energy, etching conditions, gray level, and visibility criterion. The results obtained by the software, using five different V functions, were compared with the experimental data found in the literature. Application of two functions in this software reproduced experimental data very well, while other three gave lower sensitivity than experiment.

Detection efficiency of a disk shaped detector with a critical detection angle for particles with a finite range emitted by a point-like source.

Detection efficiency of a circular detector for particles with a finite range, emitted from a point-like source was investigated, taking a critical detection angle into account. Particles emitted from the source lose some of their energy in the surrounding medium, before entering the detector material. Incident-energy dependence of the critical detection angle was taken into account. The part of the detector exposed to the particles impacting at angles greater than the critical angle (with respect to the detector surface), was determined. Several different cases were investigated, depending on the radius of the detector and the position of the detector with respect to the source. Detection probability expressions were derived for each of the cases. Results obtained using these expressions were compared with Monte Carlo calculations.

Hit probability of a disk shaped detector with particles with a finite range emitted by a point-like source.

An analytical analysis of the geometrical efficiency of a circular detector for particles with a finite range, emitted from a point-like source, is given. Several different cases were determined, depending on the particle range, radius of the detector and the position of the source with respect to the detector. These cases were analyzed separately and different expressions for calculating the hit probability were obtained for each of them. Results were compared with Monte Carlo calculations and good agreement was found. The problem considered here might be relevant for alpha-particle detection under specific conditions.

Determinants of bistability in induction of the Escherichia coli lac operon.

The authors have developed a mathematical model of regulation of expression of the Escherichia coli lac operon, and have investigated bistability in its steady-state induction behaviour in the absence of external glucose. Numerical analysis of equations describing regulation by artificial inducers revealed two natural bistability parameters that can be used to control the range of inducer concentrations over which the model exhibits bistability. By tuning these bistability parameters, the authors found a family of biophysically reasonable systems that are consistent with an experimentally determined bistable region for induction by thio-methylgalactoside (TMG) (in Ozbudak et al. Nature, 2004, 427; p. 737). To model regulation by lactose, the authors developed similar equations in which allolactose, a metabolic intermediate in lactose metabolism and a natural inducer of lac, is the inducer. For biophysically reasonable parameter values, these equations yield no bistability in response to induction by lactose - only systems with an unphysically small permease-dependent export effect can exhibit small amounts of bistability for limited ranges of parameter values. These results cast doubt on the relevance of bistability in the lac operon within the natural context of E. coli, and help shed light on the controversy among existing theoretical studies that address this issue. The results also motivate a deeper experimental characterisation of permease-independent transport of lac inducers, and suggest an experimental approach to address the relevance of bistability in the lac operon within the natural context of E. coli. The sensitivity of lac bistability to the type of inducer emphasises the importance of metabolism in determining the functions of genetic regulatory networks.