Analysis of radionuclide transfer factors from soil to plant in tropical and subtropical environments.

In this study, the factors that influence the variability of soil to plant radionuclide transfer factors (TF) in tropical and subtropical environments were statistically analyzed. More than 2,700 TF values were obtained from the literature, and from this four broad soil groups and 13 plant groups were investigated. Additionally, different plant compartments were distinguished. The wide variability and uncertainty observed in TF is considerably reduced when data are independently grouped into groups of plant/plant part/soil type combinations. In most plant groups Zn and Sr have the highest transfer values. TFs are lower for Cs and the lowest TFs were found for Ra, U and Pb.

The new IAEA-372 grass-certified reference material for (40)K and (137)Cs.

A new grass-certified reference material characterized for (137)Cs and (40)K has been issued by the International Atomic Energy Agency. Characterization of this material was conducted by a group of national metrological institutes and expert laboratories. The paper describes the process for assigning the certified reference value to the material.

Ingested soil as a source of 137Cs to ruminants.

Ingestion of soil has been identified as a potentially important source of radionuclides, particularly to grazing ruminants. Soil artificially contaminated with radiocaesium was administered orally each day for 33 days to Bergamasca sheep and the transfer to milk measured. Two soil types were used, with a clay content of 11% and 16%, respectively. Transfer coefficient (fm) values to sheep milk, calculated at the equilibrium (period from 7th to 21st day after soil administration), were 3.72 x 10(-4) days l-1 (S.D. = 7.2 x 10(-5) days l-1) and 6.11 x 10(-4) days l-1 (S.D. = 9.1 x 10(-5) days l-1), respectively for the two soils. These low values indicate that radiocaesium is not removed from the binding sites on the clay minerals in the gut of the sheep.

Transfer of Chernobyl fall-out caesium radioisotopes in the cow food chain.

From February to October 1987 samples of milk, grass and other components of the cow diet were regularly collected and analyzed for their radiocaesium contents in 26 sampling stations in a north-eastern region of Italy (Friuli-Venezia Giulia). In this paper we report the feed-to-milk transfer factors for radiocaesium obtained in 13 farms of this region of Italy.

Adhesion of water-borne particulates on freshwater biota.

The retention of suspended particles transported by river flow on surfaces of freshwater plants is a potentially important process in the contamination of aquatic biota. Field experiments have been performed to test the role of benthic algae (periphyton) in trapping inorganic suspended solids transported by the river water and to discriminate between the caesium content of periphyton caused by the adherence of inorganic solids and by the active uptake inside the organisms. The contribution of caesium of suspended solids adhering to biotic surfaces was estimated by determining the scandium content (scandium method). The scandium method was used because this element is geologically ubiquitous in soils and it is not taken up actively by plants and other organisms. The mass of suspended particles retained on the surfaces of microorganisms growing on submerged substrates were determined by comparing the scandium content of suspended material with that in algal communities. Neutron activation analysis was used as the analytical method for determination for both scandium, and caesium. The results indicate that the suspended particle fraction can contribute up to 80% of the caesium contamination of periphyton samples. Active caesium uptake and accumulation by aquatic biota represents the remaining 20% of the total caesium contamination.

Radioecological survey at selected sites hit by depleted uranium ammunitions during the 1999 Kosovo conflict.

A field study, organised, coordinated and conducted under the responsibility of the United Nations Environment Programme (UNEP), took place in Kosovo in November 2000 to evaluate the level of depleted uranium (DU) released into the environment by the use of DU ammunition during the 1999 conflict. Representatives of six different scientific organisations took part in the mission and a total of approximately 350 samples were collected. During this field mission, the Italian National Environmental Protection Agency (ANPA) collected water, soil, lichen and tree bark samples from different sites. The samples were analysed by alpha-spectroscopy and in some cases by inductively coupled plasma-source mass spectrometry (ICP-MS). The 234U/238U and 235U/238U activity concentration ratios were used to distinguish natural from anthropogenic uranium. This paper reports the results obtained on these samples. All water samples had very low concentrations of uranium (much below the average concentration of drinking water in Europe). The surface soil samples showed a very large variability in uranium activity concentration, namely from approximately 20 Bq kg(-1) (environmental natural uranium) to approximately 2.3 x 10(5) Bq kg(-1) (approximately 18000 mg kg(-1) of depleted uranium), with concentrations above environmental levels always due to DU. The uranium isotope measurements refer to soil samples collected at places where DU ammunition had been fired; this variability indicates that the impact of DU ammunitions is very site-specific, reflecting both the physical conditions at the time of the impact of the DU ammunition and any physical and chemical alteration which occurred since then. The results on tree barks and lichens indicated the presence of DU in all cases, showing their usefulness as sensitive qualitative bio-indicators for the presence of DU dusts or aerosols formed at the time the DU ammunition had hit a hard target. This result is particularly interesting considering that at some sites, which had been hit by DU ammunition, no DU ground contamination could be detected.

Plutonium, 241Am, 90Sr, and 137Cs concentrations in some Antarctic matrices.

A radioecological survey in Antarctica shows that the 239 + 240Pu, 238Pu, 241Am, 90Sr, and 137Cs activities were detectable in nearly all the samples. The activity level of 239 + 240Pu, 241Am, and 137Cs in antarctic sediments was about 5-20 times lower than in the northern Adriatic Sea sediments, but the 238Pu activities were relatively high. It was interesting to note that the 90Sr concentrations in all the sediments tended to be low, which could be the result of the easier exchangeable behavior of 90Sr in water. High concentrations were detected in mosses and lichens and their activity levels were comparable to those in central Italy. The radionuclide ratio analyses show that the major part of 239 + 240Pu, 241Am, 90Sr, and 137Cs was a result of nuclear weapon tests. The higher 241Am/239 + 240Pu ratio was observed and it could perhaps be the result of fallout of nuclear weapon tests prior to 1962. The 238Pu/239 + 240Pu ratio in the antarctic matrices was about seven times higher than in the Northern hemisphere and it could be inferred that the major part of 238Pu was originating from the SNAP-9A satellite accident.

Vertical transport of radiocesium in surface soils: model implementation and dose-rate computation.

A mathematical model on the Radionuclide Behaviour in Soil for the study of the migration of radionuclides in undisturbed soil profile has been developed. The model has been calibrated using 134Cs and 137Cs concentrations along soil samples gathered in a natural grassland and beech wood, respectively, located in the Friuli-Venezia Giulia region (northeastern part of Italy). In these sampling sites, the external exposure due to 134Cs and 137Cs distribution along the soil profile has been also assessed.

Radioecological software package: an interactive computational system to simulate the behaviour of radionuclides in semi-natural environments.

RSP (Radioecological Software Package) is an interactive support system that simulates the behaviour of radionuclides in semi-natural environments and the consequences on the population in terms of the external exposure. RSP consists of three modules: the first one, soil mobility, simulates the vertical transport of radionuclide in soil using the mathematical model RABES. The second module, soil -to-plant transfer, simulates the radionuclide soil-to-plant transfer factor reported in the literature. Soil properties, vegetation types and environmental conditions are taken into consideration in the simulation process. In the third module, dose assessment, the dose-rate factor in air at a height of 1 m above ground can be calculated for sources distributed in a slab of finite thickness dn sources which are exponentially distributed with depth. The calculations are performed using DAGES Model, a Monte Carlo algorithm developed to simulated the photon transport for the soil/air configuration. A free copy of RSP can be downloaded from the website: http://imasl-apat.unsl.edu.ar.

Suspended particle adhesion on aquatic plant surfaces: implications for 137Cs and 133Cs uptake rates and water-to-plant concentration ratios.

Suspended particle adhesion on aquatic biota can significantly increase the apparent concentration of radionuclides above their endogenous value, leading to an overestimation of the uptake rate and concentration ratios. This study is an attempt to assess quantitatively the importance of suspended particle adhesion on periphyton samples (biological material coating submerged surfaces). The concentrations of 137Cs and stable Cs (133Cs) in periphyton, suspended particles and filtered water were measured to determine the net water-to-periphyton concentration ratios for 137Cs and stable Cs. The net amount of 133Cs (or 137Cs) taken up by periphyton was calculated by subtracting from the total amount of 133Cs (or 137Cs) on the collected material (periphyton + inorganic particles), the 133Cs (or 137Cs) due to the inorganic particles adhering to periphyton. The mass of suspended particles adhering to the periphyton surface was calculated using scandium as an indicator of the mineral fraction of the suspended particles. The relationship between the concentration ratios for 137Cs and stable Cs and suspended particle adhesion on periphyton external surfaces is discussed.

Levels of depleted uranium in Kosovo soils.

The United Nations Environment Programme (UNEP) has performed a field survey at 11 sites located in Kosovo, where depleted uranium (DU) ammunitions were used by the North Atlantic Treaty Organization (NATO) during the last Balkans conflict (1999). Soil sampling was performed to assess the spread of DU ground contamination around and within the NATO target sites and the migration of DU along the soil profile. The 234U/238U and 235U/238U activity concentration ratios have been used as an indicator of natural against anthropogenic sources of uranium. The results show that levels of 238U activity concentrations in soils above 100 Bq x kg(-1) can be considered a 'tracer' of the presence of DU in soils. The results also indicate that detectable ground surface contamination by DU is limited to areas within a few metres from localised points of concentrated contamination caused by penetrator impacts. Vertical distribution of DU along the soil profile is measurable up to a depth of 10-20 cm. This latter aspect is of particular relevance for the potential risk of future contamination of groundwater.

The new IAEA reference material: IAEA-434 technologically enhanced naturally occurring radioactive materials (TENORM) in phosphogypsum.

A reliable determination of Technologically Enhanced Naturally Occurring Radioactive Materials in phosphogypsum is necessary to comply with radiation protection and environmental regulations. In this respect, a new phosphogypsum reference material was produced and certified to assist in the validation of analytical methods and the quality assurance of produced analytical results. This paper presents the sample preparation methodology, material homogeneity assessment, characterization campaign results and assignment of property values, and associated uncertainties. The reference values and associated uncertainties for Pb-210, Ra-226, Th-230, U-234 and U-238 were established based on consensus values calculated from analytical results reported by three National Metrology Institutes and five expert laboratories.

Influence of crop types and soil properties on radionuclide soil-to-plant transfer factors in tropical and subtropical environments.

This paper presents a descriptive statistical analysis of radionuclide soil-to-plant transfer factors (Fv) for tropical and subtropical environments. These values were collected from previous databases and standard publications with the objective of contributing to the IAEA Technical Report Series: Handbook of parameter values for the prediction of radionuclide transfer to humans in terrestrial and freshwater environments. More than 2200 Fv values of different radionuclides were gathered and arranged into specific databases, detailing relevant information regarding the environments where this parameter was calculated. This study explores the dependence of Fv values to crop types, and soil properties. The wide variability and uncertainty observed in calculated Fv values were considerably reduced when the data was independently grouped into clusters containing the same radionuclide/plant group/soil type combinations. For each cluster the principal statistical quantities were determined. Using these quantities, the Fv distributions of each data set was explored. Fv probability distribution is discussed to clarify the use of this empirical parameter in radioecological and radiological assessment models.

Validation of rapid methods for the determination of radiostrontium in milk.

A rapid method of (89)Sr and (90)Sr comprising ion chromatography for preconcentration and Sr extraction chromatography for separation of Sr from Ca, Ba and Y was validated with spiked milk samples. An (89)Sr/(90)Sr activity ratio of up to 12 showed the relative bias was within +/-20%. The separation time of Sr was 7h and the chemical recovery of Sr ranged from 80% to 95%. The detection limit for 500 mL milk and 90 min counting time was 0.1 Bq L(-1).

Matrix materials for proficiency testing: optimization of a procedure for spiking soil with gamma-emitting radionuclides.

The IAEA Reference Materials Group of the Chemistry Unit, Agency's Laboratories Seibersdorf, has developed and optimized a procedure for spiking some environmental matrices with gamma-emitting radionuclides. This paper describes the spiking procedure, homogeneity testing of the spiked material, and assignment of property values and their associated uncertainties for the radionuclides 54Mn, 65Zn, 60Co, 109Cd, 134Cs, 137Cs, 210Pb, and 241Am. This procedure has already been successfully used in an IAEA proficiency test on the determination of 137Cs and 210Pb in spiked soil and has been found to be appropriate for production of soil materials for proficiency testing and internal quality control samples. The main advantage of this procedure is a low uncertainty arising from heterogeneity, which was found to be less than 1.2% for all the analytes studied.

Environmental radioactivity in four national parks of the Abruzzo region (central Italy).

Since 1998, the Istituto Zooprofilattico Sperimentale dell'Abruzzo e Molise 'G. Caporale' in Teramo is conducting radioecological surveys in the Abruzzo region (Central Italy), to acquire knowledge on the geochemical and biological mobility of radionuclides derived from the Chernobyl accident. To this end, samples of grasses, fungi, mosses and soils were collected in four national parks (Sirente-Velino, Abruzzo Lazio and Molise, the Gran Sasso and the park of Monti della Laga and Maiella). The results show that the Chernobyl fallout is still detectable in the samples collected in the four parks but the (137)Cs concentrations are present in the semi-natural environments in quantities that do not create concerns from a radiological point of view.

Analysis of the contribution of forest pathways to the radiation exposure of different population groups in the Bryansk region of Russia.

The experience gained in the aftermath of serious radiation accidents shows that forests are an important source of external and internal exposure of the affected population. This paper presents the results of an assessment of the major radiological consequences for forests of Russia, most heavily contaminated after the Chernobyl nuclear power plant (ChNPP) accident. Illustrated in the Novozybkovsky district of the Russian Federation, the significance of different forest exposure pathways is estimated and the doses resulting from forest pathways are compared with the doses from agricultural products. It has been found that the contribution of mushrooms and berries to the internal doses of the population, relative to the doses from agricultural products, varied from 10-15% in 1987 to 40-45% in 1996. The results indicate large differences in internal exposure of members of the "critical groups" and "normal population", increasing with time after deposition. Data are presented that give information on the contribution of forests to the collective doses of inhabitants of the area under consideration. It has been shown that for 10 years after the accident (1987-1996), the contribution of forest products to the collective dose of the rural population living in contaminated forests of the Novozybkovsky district, amounts to about 20% (213 person Sv) of the total collective dose of internal and external exposures. However, a potential impact of these products including the dose from exported products is much higher and might reach 659 person Sv. It has been found that in the long-term after the ChNPP accident, serious attention should be given to forest countermeasures, and restoration strategies should be selected on the basis of a combined analysis of the effectiveness of forest and agricultural countermeasures.

210Pb and 210Po determination in environmental samples

Sequential separation of 210Pb and 21OPo in environmental samples allows the determination of these naturally occurring radionuclides with good chemical yields and low detection limits. After sample mineralization, part of the leaching solution is used for 210Po determination which does not require any further treatment and essentially quantitative recoveries are obtained, using a standard 209Po tracer. The remaining part of the leaching solution is used for 210Pb determination. Starting from 3 g sediment (30 l water), the lower limits of detection of the method are 1.4 Bq kg(-1) (0.14 mBq l(-1)) for 210Pb and 0.25 Bq kg(-1) (0.016 mBq l(-1)) for 21OPo. The procedure has been checked by analysing two certified reference materials, supplied by IAEA, and reliable results have been obtained.