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In this work, removal of heavy metals (Cr, Mn, Co, Ni, Cu, Zn, As, Cd, and Pb) from fly ash has been studied using acid leaching and wet oxidation methods. In parallel, microwave-assisted acid digestion was applied for determination of pseudo-total concentrations of heavy metals to estimate the leaching efficiency. Multivariate statistics (Pearson correlation, principal component analysis, and hierarchical cluster analysis) have shown two dominant groups of elements, depending on their characteristics and affinity towards the ash solid phase. Thus, Cr, Zn, Mn, Co, and Ni belong to the group I, while Pb, As, Cd, and Cu belong to the group II. It was demonstrated that the wet oxidation method was more suitable than acid leaching since the reduction in metal concentration was 30 to 75 % compared to 12 to 25 % obtained by acid digestion. The influence of fly ash treatment on the residue characteristics was investigated by X-ray diffractometry and scanning electron microscopy. The analyses revealed surface and structure changes of fly ash after the wet oxidation treatment. Overall, wet oxidation could be an appropriate treatment for heavy metal removal from fly ash, providing a material that could be further used, thus reducing the risk of pollution caused by the disposal of coal combustion fly ash.

Seventeen water-soluble substances (of sodium, ammonium, potassium, magnesium, calcium, formate, methanesulfonate, glyoxylate, chloride, nitrite, nitrate, glutarate, succinate, malate, malonate, sulfate and oxalate) in 94 samples of particle matter in the ambient air, collected over ten months, in a suburb of Belgrade (Serbia), were determined by ion chromatography. To apportion the sources of the air pollution, the log-transformed data were processed by applying multivariate techniques. Principal component and factor analysis identified three main factors controlling the data variability: stationary combustion processes with the highest loadings of oxalate, malonate and malate; landfill emission and secondary inorganic aerosol characterized by high levels of ammonium, nitrate and sulfate; a contribution of mineral dust composed of magnesium, calcium and chloride. The hierarchical cluster analysis pointed out a differentiation of the samples into five groups belonging to different variables inputs. For the classification of ambient air samples using nine selected ions, the recognition ability of linear discriminant analysis, k-nearest neighbors, and soft independent modeling of class analogy were 87.0, 94.6, and 97.8 %, respectively. Time-series analysis showed that the traffic emission is more pronounced in winter in contrast to the mineral dust influence, while the effect of waste combustion exhibits no trend.

A novel magnetic polymer/bentonite composite was prepared by suspension copolymerization of glycidyl methacrylate and ethylene glycol dimethacrylate in the presence of magnetic bentonite (MB-PGME) and functionalized with ethylene diamine and hexamethylene diamine (MB-PGME-ED and MB-PGME-HD). The obtained samples were characterized in terms of structure as well as thermal, magnetic and morphological properties. The sorption of rhenium (Re) and tungsten (W) from aqueous solution onto MB-PGME-ED and MB-PGME-HD was investigated considering their contact time and different initial ion concentration, giving possibility for usage of these composites as commercial sorbents. The sorption system follows the pseudo-second order and intraparticle diffusion kinetic models. The results indicated a better fit with the Freundlich isotherm model.

This study is aimed to evaluate the possibility of lemon peel, as an agro-industrial waste, to remove Fe2+, Zn2+ and Mn2+ from single aqueous solutions and mining wastewater. For this purpose, the influence of various parameters: sorption time, initial pH solution, initial metal ion concentration and a dose of sorbent on the sorption process were studied in batch experiments. The experimental equilibrium data have been analysed utilizing linearized forms of Langmuir, Freundlich, Temkin and Dubinin–Radushkevich isotherms. The Langmuir isotherm provided the best theoretical correlation of the experimental equilibrium data for Fe2+, Zn2+ and Mn2+, with the maximum sorption capacities of 4.40, 5.03 and 4.52 mg g-1, respectively. The percentage of targeted ions removal from single aqueous solutions was 92.9 % (Zn2+), 84.5 % (Fe2+) and 78.2 % (Mn2+). Regarding the sorption capability of lemon peel in mining wastewater, the maximum removal of Fe2+, Zn2+ and Mn2+ from mining wastewater was 49.62, 33.97 and 9.11 %, respectively. In addition, the potential reusability of the lemon peel as sorbent was investigated through desorption study in 0.1M of CH3COO4, HCl and HNO3 solution. The highest rate of desorption was achieved in 0.1 M HCl solution, reached a value of 55.19 % for Mn2+ and 37.24 % for Zn2+, while for Fe2+ the highest value of 25.82 % was achieved in 0.1M HNO3 solution.

Polymer-based, highly porous nanocomposites with functionalized ligands attached to the core structure are extremely efficient in the detection, removal and recovery of metals through the process of sorption. Quantumchemical models could be helpful for sorption process analyses. The sorption of Cu(II) ions by amino-functionalized chelating macroporous copolymers poly(GMA-co-EGDMA)-amine and sorption selectivity of the subject copolymers, ethylenediamine (en), diethylenetriamine (dien) and triethylenetetramine (trien), were successfully modelled by quantum chemical calculations. Considering the crystal structures from CSD and experimental conditions during the formation of metal complexes, the most frequent mononuclear complexes are those with the tetradentate teta ligand, while binuclear complexes are formed when the metal ion is in large excess. Although the en-copolymer was the most effective functionalized one, higher maximum sorption capacities (Qmax) were observed for the dien- and trien-copolymers, due to their abilities to form binuclear complexes. The enthalpy term has the greatest contribution to the total Gibbs energy change of reaction for the formation of mononuclear Cu(II) complexes (ΔGaq), while the solvation energy of the reaction has the greatest contribution in the formation of binuclear complexes. The results of the study indicate that small amines with the ability to form binuclear complex are the best choice for functionalization of the considered copolymer. [Projects of the Serbian Ministry of Education, Science and Technological Development, Grant no. OI 172043, Grant no. 172023 and Grant no. III 43009]

The two retention models, the linear solvent strength model (LSS) and the quadratic relationship, in addition to artificial neural network (ANN) approach, were compared in their ability to predict the retention behaviour of common cations (Li, Na, NH4, K, Mg, and Ca) in isocratic ion chromatography using the methanesulfonic acid (MSA) eluent. Over wide variations in the MSA concentration, the quadratic model shows a quite good prediction power. LSS can be used only for monovalent cations and in the proximity of the experimental design point. ANN fails to predict the retention for the data not included in the training set. To find the optimal conditions in the experimental design, the normalized resolution product as a chromatographic objective function was employed. The optimum MSA concentration in the eluent on a Dionex CS12 column was found to be 18 mM, with the total analysis time of less than 10 min. [Projekat Ministarstva nauke Republike Srbije, br. III43009]

A series of poly(2-hydroxyethyl acrylate-co-itaconic acid), P(HEA/IA), hydrogels with different HEA/IA ratio, were synthesized using free radical crosslinking/copolymerization and investigated as sorbents for Pb2+ ions from aqueous solutions. Hydrogels were characterized using DMA, FTIR, DSC, SEM and AFM. The adsorption was found to be highly dependent on hydrogel composition, solution pH, sorbent weight, ionic strength and contact time. Five isotherm models, Langmuir, Freundlich, Redlich-Peterson, Temkin and Dubinin-Radushkevich, were applied to the sorption data. The best fit was obtained with Redlich-Peterson isotherm. The separation factor, RL, value indicated favorable sorption for Pb2+ ions. The maximum sorption capacities were 392.2 and 409.8 mg/g for P(HEA/2IA) and P(HEA/10IA), respectively. Kinetic data showed best fit with pseudo-second-order model. Thermodynamic studies revealed that the reaction was exothermic and proceeds with a decrease in entropy. Moreover, P(HEA/IA) hydrogel showed the most pronounced sorption toward Pb2+ ions from environment containing Cu2+, Zn2+, Cd2+, Ni2+ and Co2+ ions. Sorption/desorption experiments, showed that the P(HEA/IA) hydrogels could be reused without significant loss of the initial properties even after three adsorption-desorption cycles. [Projekat Ministarstva nauke Republike Srbije, br. 172015 i br. 172062]

Interpretive retention modeling was utilized to optimize the isocratic ion chromatographic (IC) separation of the nine anions (formate, fluoride, chloride, nitrite, bromide, nitrate, phosphate, sulfate, oxalate). The carbonate-bicarbonate eluent was used and separation was done on a Dionex AS14 ion-exchange column. The influence of combined effects of two mobile phase factors, the total eluent concentration (2 - 6 mM) and the carbonate/bicaronate ratio from 1:9 to 9:1 (which corespondent to pH range 9.35 - 11.27), on the IC separation was studied. The multiple species analyte/eluent model that takes into account ion-exchange equilibria of the eluent and sample anions was used. In order to estimate the parameters in the model, a non-linear fitting of the retention data, obtained at two-factor three-level experimental design, was applied. To find the optimal conditions in the experimental design, the normalized resolution product as a chromatographic objective function was employed. This criterion includes both the individual peak resolution and the total analysis time. A good agreement between experimental and simulated chromatograms was obtained. [Projekat Ministarstva nauke Republike Srbije, br. III43009]

A novel method combining a traditional immersion precipitation process for making membranes with photopolymerization and crosslinking of functional monomers included in the casting solution was used to prepare asymmetric polyethersulfone membranes with submicron particles incorporating glycidyl methacrylate copolymer. In order to introduce sulfonic groups epoxide rings of glycidyl methacrylate were opened using two methods. The first method was functionalization with sodium sulfite, and the second method was functionalization with sulfuric acid and then grafting with 2-acrylamido-2-methylpropane sulfonic acid. Obtained membranes were characterized using infrared spectroscopy, conductometric titration and water permeability measurements. Scanning electron microscopy and atomic force microscopy were used to investigate the surface morphology and topology of membrane. Dynamic adsorption of Rhodamine B as a model dye was used to demonstrate suitability of these novel membranes for membrane adsorption since the adsorption capacity for dye cations was much better for both functionalized membrane with sodium sulfite and grafted membrane with 2-acrylamido-2-methylpropane sulfonic acid compared to the nonfunctionalized membrane. [Projekat Ministarstva nauke Republike Srbije, br. TR32008 and III 43009]

Synthesis of an unconventional resin based on 4-vinylpyridine (4-VP) and its Cu(II) sorption behavior were studied. Three samples of macroporous crosslinked poly(4-vinylpyridine-co-ethylene glycol dimethacrylate) [P4VPE] with different porosity parameters were prepared by suspension copolymerization by varying the n-heptane amount in the inert component. The samples were characterized by mercury porosimetry, elemental analysis and x-ray photoelectron spectroscopy (XPS). The sorption of P4VPE for Cu(II) ions, determined under non-competitive conditions, was relatively rapid, i.e. the maximum capacity was reached within 30 min. The maximum experimental sorption capacity for the sample with the highest values of pore diameter and specific pore volume (Sample 3, Qeq = 89 mg g-1) was 17.5 times higher than for the sample with the lowest values of pore diameter and specific pore volume (Sample 1, Qeq = 5.1 mg g-1). Since the values for pyridine content in all P4VPE samples were almost the same, it was concluded that the porosity parameters have predominant influence on Cu(II) sorption rates on P4VPE. The sorption behavior and the rate-controlling mechanisms were analyzed using six kinetic models (pseudo-first order, pseudo-second order, Elovich, intraparticle diffusion, Bangham and Boyd models). XPS study clarified the nature of the formed P4VPE-Cu(II) species. [Projekat Ministarstva nauke Republike Srbije, br. TR 37021 i br. III 43009]

Resorcinol-formaldehyde carbon cryogel has been prepared, characterized and used for the removal of commonly used herbicide clopyralid from the aqueous solutions under varying experimental conditions. Carbon has shown a relatively high specific surface area, significant mesoporosity and an amorphous structure. A set of the following isotherm models has been used to interpret the equilibrium data: Langmuir, Freundlich, Temkin, Dubinin-Radushkevich, Jovanović, Hurkins-Jura, and Helsey model. Several models have fitted well although the calculated values for qmax poorly correlate with the data obtained experimentally. The kinetic models of the pseudo-first and pseudo-second-order, the models of Elovich, Bangham and the intraparticle diffusion model have been used for fitting the kinetic data. The rate of the process is fast in the beginning while adsorption equilibrium is attained not until 24 hours. Adsorption was found to be pH dependent and favored in acidic solutions.

Among radionuclides in the soil deposited after Chernobyl accident, 137Cs poses considerable environmental and radiological problems because of its relatively long half-life (30.17 y), its abundance in the fallout, high mobility and similarity to potassium as the major plant nutrient. In this study the samples of undisturbed surface soil (n=250) were taken from 70 regions in Belgrade, during 2006-2010. The specific activities of 137Cs were measured by gamma-ray spectrometry. Based on obtained results external effective dose rates were calculated according to the internationally accepted activity to dose rate conversion equations. The specific activities of 137Cs were geographically mapped. The presence of 137Cs has been detected in all soil samples, with high variability of its specific activity, ranging from 3 Bq kg-1 to 87 Bq kg-1. The mean specific activity of 137Cs was 23 Bq kg-1 and the corresponding absorbed dose was 1.5 nSv h-1. The observed range reflects the inhomogeneity of the deposition process following the Chernobyl accident. It could also be attributed to topographic differences and spatial differences in physicochemical and biological soil properties, soil type and vegetation cover. The results of the present study could be valuable database for future estimations of the impact of radioactive pollution.

The main causes of efficiency loss in thermal power plants are boiler tube failures that diminish unit reliability and availability, and raise the cost of the electric energy. For that reason, regular examination of boiler tubes is indispensable measure for prevention future malfunctions of power units. Microscopic examination of economizer inner wall microstructure, analysis of chemical composition of deposit using x-ray diffraction (XRD) and scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) has been performed in a subcritical power plant. Stress corrosion cracking, pitting corrosion, destroyed protective magnetite layer, presence of magnetite and hematite in deposit and corrosive impurities within the cracks were indicated the effect of inadequate quality of feedwater that can not entirely ensure reliable operation of the boiler. It may be stated that maintenance of present boiler does not provide its reliable operation. Extensive chemical control of water/steam cycle was recommended. [Projekat Ministartsva nauke Republike Srbije, br. III 43009 i br. III 45012]

Arsenic exists in the form of various chemical species differing by their physicochemical behavior, in toxicity, bioavailability and biotransformation. The determination of arsenic species is an important issue for environmental, clinical and food chemistry. However, differentiation of these species is a quite complex analytical task. Numerous speciation procedures have been studied that include electrochemical, chromatographic, spectrometric and hyphenated techniques. This review comprehends the relevant research in the field of arsenic speciation analysis with novel applications and significant advances. Stability of arsenic species and each of the analytical steps (sample collection, storage, preservation, extraction) of the arsenic speciation methods was particularly evaluated. Analytical validation and performance of these methods are also reviewed.

The photocatalytic degradation of synthetic textile dye CI Basic Yellow 28 (BY28) in water, using recently synthesized P160 TiO2 based catalyst, under Osram ultra-vitalux® lamp (300 W) light, was studied. The effect of the operational parameters such as initial concentration of catalyst, initial dye concentration and pH was studied. Salt effect was also investigated (NaCl, Na2CO3, Na2SO4, NaNO3). It was found that the optimal concentration of catalyst is 2.0 g L-1. A pseudo first-order kinetic model was illustrated using the Langmuir-Hinshelwood mechanism, and the adsorption equilibrium constant and the rate constant of the surface reaction were calculated (KBY = 6.126 L mg-1 and kC = 0.272 mg L-1 min-1, respectively). The photodegradation rate was higher in weak acidic than in high acidic and alkaline conditions. The presence of CO32- ions increases the photodegradation rate while Cl-, SO42- and NO3-ions decreases the reaction rate. The rate of photodegradation of BY28 was measured using UV-Vis spectroscopy. [Projekat Ministarstva nauke Republike Srbije, br. III 45019 and br. 172013.]

Adsorption of a cationic phenothyazine dye methylene blueonto activated carbon prepared from pine cones was investigated with the variation in parameters of contact time, dye concentration and pH. The kinetic data were found to follow the pseudo-second-order kinetic modelclosely. The equilibrium data were best represented by the Langmuir isotherm with maximum adsorption capacity of 233.1 mg g-1. Adsorption was favored by using a higher solution pH. Textural analysis by nitrogen adsorption was used to determine specific surface area and pore structure of the obtained carbon. Boehm titrations revealed that carboxylic groups are present in the highest degree on the carbon surface. The results indicate that the presented method for activation of pine cones could yield activated carbon with significant porosity, developed surface reactivity and considerable adsorption affinity toward cationic dye methylene blue.

Commercial macroporous poly(4-vinylpyridine-co-divinylbenzene) [P4VPD], known as REILLEX-425 was characterized by mercury porosimetry, nitrogen physisorption, Fourier transformed infrared (FTIR) spectroscopy and elemental analysis. Sorption rates of P4VPD for Cu(II), Co(II) and Cr(VI) ions were determined in static non-competitive experiments, at room temperature (298 K). Rapid sorption was observed, especially for Co(II), with half time, t1/2, of 1.5 min and high experimental maximal capacity, Qmax, of 3.08 mmol g-1. Four kinetic models (pseudo-first and pseudo-second order model, intraparticle diffusion and Boyd model) were used for analyzing metal sorption by P4VPD. Metal ions sorption is well represented by the pseudo-second-order model, with definite influence of pore and film diffusion on sorption rates. [Projekat Ministarstva nauke Republike Srbije, br. III43009]

An inverse gas chromatographic (IGC) study of the sorption properties of macroporous crosslinked poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate), PGME, and PGME modified with ethylene diamine, PGME-en, was presented. At infinite dilution, the thermodynamic parameters of adsorption, the dispersive components of the surface free energies, the acid/base constants and the interaction parameters for the initial and modified copolymer samples were investigated. The adsorption isotherms determined by IGC under conditions of finite surface coverage were used to estimate the surface area, the isosteric heat of adsorption and the adsorption energy distribution on the surface of the initial and modified copolymer samples. .

The possibility of polymer characterization by inverse gas chromatography (IGC) was illustrated with the study of sorption properties of macroporous crosslinked poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate), PGME, synthesized by suspension copolymerization, and copolymer modified with ethylene diamine, PGME-en. The data collected from IGC experiments at infinite dilution are used for the calculation of the thermodynamic parameters of adsorption, dispersive components of the surface free energies, and the acid/base constants. .

Macroporous crosslinked poly(GMA-co-EGDMA) was synthesized by the suspension copolymerisation and functionalized by the ring-opening reaction of the pendant epoxy groups with ethylene diamine. The porosity parameters (specific pore volume, specific surface area, and pore diameter, which corresponds to half of the pore volume) for the initial and amino-functionalized copolymer samples were calculated from the cumulative pore volume distribution curves obtained by mercury porosimetry. The selectivity, sorption capacity and sorption rate of amino-functionalized poly(GMA-co-EGDMA)-en were determined under static conditions. The sorption of Cu(ll) and Ag(l) ions on poly(GMA-co-EGDMA)-en was very rapid (ti/2 value about 1 min). Slower sorption was observed for Au(lll) ions with a ti/2 value of 6.5 minutes. The different rates of Au(lll), Cu(ll) and Ag(l) sorption could be applied for gold, copper and silver ion separation from mixed solutions. The sorption of Ni(ll) and Cu(ll) ions from galvanic solution under competitive conditions was also fast, with ti/2 values of 0.5 and 2 min, respectively. However, Zn(ll) sorption was considerably slower (a ti/2 of 10 min). Similar results were obtained for galvanic solution under dynamic conditions, i.e., the metal sorption capacities of poly(GMA-co-EGDMA)-en decreased in the order: Ni(ll) > Cu(ll) >> Zn(ll). The reusability of amino-functionalized poly(GMA-co-EGDMA) for Cu(ll) sorption was tested in four sorption/desorption cycles. Regeneration experiments were performed with 0.1 and 1 M H2SO4 showed a Cu(ll) capacity loss of 50 % in the first sorption/desorption cycle. The sorption capacity increased when additional neutralization with 0.1 and 1 M NaOH was performed after each sorption/desorption cycle.

A suppressed ion chromatography (IC) technique, using a carbonate/hydrogen carbonate or a hydroxide eluent, has been evaluated as a monitoring tool for the detection of major anions (F-, Cl-, NO3-, PO43- and SO42-) in ultra pure water and condensed steam from thermal power plants. An electrical conductivity detector with an anion-exchange column (IonPac AS14), an auto self-regenerating suppressor (ASRS), and an isocratic high-pressure pump system were used for the detection of low concentrations of inorganic anions. It was shown that the suppressed IC technique provides a suitable means for preventing possible damage to generating equipment in power plants. The detection limits of the method for the anions of interest were < 0.3 μg/L.

A feed-forward artificial neural network (ANN) model was used to link molecular structures (boiling points, connectivity indices and molecular weights) and retention indices of polycyclic aromatic hydrocarbons (PAHs) in linear temperature- programmed gas chromatography. A randomly taken subset of PAH retention data reported by Lee et al. [Anal. Chem. 51 (1979) 768], containing retention index data for 30 PAHs, was used to make the ANN model. The prediction ability of the trained ANN was tested on unseen data for 18 PAHs from the same article, as well as on the retention data for 7 PAHs experimentally obtained in this work. In addition, two different data sets with known retention indices taken from the literature were analyzed by the same ANN model. It has been shown that the relative accuracy as the degree of agreement between the measured and the predicted retention indices in all testing sets, for most of the studied PAHs, were within the experimental error margins (+-3 %).

Macroporous crosslinked poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate), p(GME), was synthesized by suspension copolymerization and modified by reaction of the pendant epoxy groups with ethylenediamine. The sorption rate and capacity of themodified copolymer, p(GME)-en for Rh(III) Au(III) and Pt(IV) ions were determined in batch experiments under non-competitive conditions. The uptake of Rh(III) was faster than those ofAu(III) and Pt(IV). The sorption capacity for Pt(IV)was determined in the pHrange 0.9–6.0. The maximum Pt(IV) uptake capacity onto p(GME)-en at pH 5.5 was 1.30 mmol/g.

The interactions of n-hexane, benzene, chloroform, and tetrahydrofuran with dried (amorphous) chromia (I) and chromia heated at 1073 K (crystalline) (II), both obtained from a colloidal dispersion, and a commercially available chromia (III) were studied by inverse gas chromatography (IGC) under finite surface coverage conditions. The isotherms, in the temperature range 383 – 423 K, were used to estimate the surface area, the adsorption energy distribution, the isosteric heat of adsorption, and the spreading pressure on the surfaces of the solids. The uniformly reduced adsorption ability of the heated chromia was attributed to the dehydroxylation of the surface at the higher temperatures. Both solids showed an increased affinity toward chloroform molecules, as a result of strong acid-base interaction.

A multifactor optimization strategy was utilized to predict the isocratic HPLC separation of nine phenols. The retention behavior was studied as a function of changing eluent (methanol – acetic acid) composition. The predicted and measured retentions are in rather good agreement. To locate the optimum in the factor space, the normalized resolution product criterion was applied. In virtually every case, the resolution is limited by the separation of the 2-chlorophenol and 2,4-dinitrophenol pair.

The parameters for the development of a chromatographic (HPLC) method and its validation are discused in the paper. Chromatographic analysis involves a multi-step procedure consisting of sample collection, pretreatment instrumental measurements and data processing. Emphasize was placed on the instrumental part of the analysis presuming that the contributions of the other variables were minor. The roles of precision, accuracy, detection limit, quantification limit, specificity, selectivity, range, linearity and robustness, as well as system suitability in the analytical application of chromatography were described. Recommendations for the validation of these parameters according to ICH and FDA guidelines are given. The criteria of validation described above can be almost completely applied to other instrumental chromatographic techniques such as GC, GC-MS, HPTLC, etc.

Background: Terrestrial radiation emitted from naturally occurring radionuclides, such as 40K and radionuclides from the 238U and 232Th series and their decay products represent the main external source of irradiation to the human body. The purpose of this study was to provide a preliminary assessment of the doses from terrestrial exposure of population in Serbia and to estimate a potential radiation hazard for population inhabiting investigated areas. Methods: The gamma dose rates, external hazard indexes, and annual effective doses due to terrestrial naturally occurring radionuclides (238U, 232Th and 40K) were calculated based on their activities in soil samples in Serbia as determined by gamma-ray spectrometry. Results: The total absorbed gamma dose rate due to these radionuclides varied from 16.9 to 125 nGy h-1, with a mean of 62.8 nGy h-1. Assuming a 20% occupancy factor, the corresponding annual effective dose varied from 2.07 to 15.4×10-5 Sv with the mean value of 7.7×10-5 Sv, i.e. annual effective dose was in range of the world wide average values. Conclusion: According to the values of external hazard index obtained in this study (mean Hex = 0.35), the radiation hazard was insignificant for the population living in investigated areas.