Peter Bossew

The cumulative deposition of the 137Cs fallout in Austria resulting from the passage of the Chernobyl cloud has been investigated by applying correlation dimension and hyperbolic frequency distribution methods. For the analysis, a total of 1,881 deposition values were used, which were collected by the Federal Environmental Agency of Austria and the Federal Ministry of Health, representing all available measurements of 137Cs in soil made in Austria after the Chernobyl accident. From these data a hyperbolic exponent for the frequency distribution of 4.0 and a set of fractal correlation dimensions, which decrease from 1.426 +/- 0.022 (for the whole network) to 0.706 +/- 0.047 (for 137Cs values > or = 100 kBq m(-2)), were derived, thus confirming that the fallout pattern can be described as a multifractal.

Cryoconites are airborne sediments which accumulate on the surface of glaciers. In samples of cryoconites a temperate Austrian glacier high activity concentrations of anthropogenic radionuclides were found, which stem from global and Chernobyl fallouts. Radionuclides identified were (137)Cs, (134)Cs, (238)Pu, (239+240)Pu, (90)Sr, (241)Am, (60)Co, (154)Eu, (207)Bi, and (125)Sb. Given the approximately known isotopic ratios, Cs and Pu can be separated into the contributions of either source of origin. Published (137)Cs/(134)Cs and (239+240)Pu/(238)Pu ratios were used for the discrimination of the Dachstein-glacier cryoconites according to their origin from global or Chernobyl fallout. Two different groups of cryoconites were identified, an older population dominated by nuclear weapons fallout and a younger one with predominant Chernobyl fallout. With those data a simple model was formulated to demonstrate the transition and mixing of these two populations on the glacier surface.

Within the context of its institutional scientific support to the European Commission, in 2005 the Radioactivity Environmental Monitoring (REM) group at the Joint Research Centre of the European Commission, started to explore the possibility of mapping indoor radon in European houses as a first step towards preparing a European Atlas of Natural Radiations. The main objective of such an atlas is to contribute to familiarizing the public with its naturally radioactive environment. The process of preparing the atlas should also provide the scientific community with a database of information that can be used for further studies and for highlighting regions with elevated levels of natural radiation. This document presents the status of the European indoor radon (Rn) map, first statistical results, and outlines of forthcoming challenges.

Indoor radon (Rn) concentrations have been measured intensively in many countries to assess the burden of diseases associated with exposure to this radioactive gas. So-called radon-risk maps have consequently been produced to delineate areas with high levels. Geostatistical techniques are commonly used nowadays to map a range of environmental variables, in particular to generate probability maps of exceeding a given threshold. However, very few case studies in which indoor radon measurements have been investigated using geostatistical techniques have been published so far. By analyzing around 12,000 Rn measurements made in Austrian ground floors during a 10-year survey, we aim here to review and discuss the potential of geostatistics for mapping an environmental variable that shows very strong local variability. In particular, we show how kriging of the scale components can shed new light on various factors that affect the very high spatial variability of the variable.

... Raster data are much more flexible and useful for subsequent maintenance and modelling. We have seen that handling data which present high local variability is everything but straightforward. ...Dubois, G. (2005). An overview of Radon surveys in Europe. EUR 21892 EN, EC. ...

The semivariogram can provide a description of the spatial correlation of a variable that represents a continuous function of space co-ordinates. Therefore, it is not only useful to improve sampling strategies and validate the collected data, but it can also define the main parameters that are involved in most mapping algorithms. The spatial correlation may, however, change depending on the values of the variable, which is not without consequences on the quality of the maps of radioactive deposition. This work investigates the spatial correlation for different levels of 137Cs deposited in Austria. It is shown that low levels (< 5 kBq/m2) and high levels (> 40 kBq/m2) of radioactivity present less correlation in space than the mid-levels (5-40 kBq/m2). As a result, maps establishing the probabilities to be under or above a specific deposition threshold will have an uncertainty associated to the estimated values that is directly correlated to the different levels of radioactivity.

The alpine regions of Austria were among the most contaminated territories outside of the former USSR after the Chernobyl accident. In the investigated province of Salzburg the median (137)Cs surface deposition was 31.4 kBq m(-2) with maximum values exceeding 90 kBq m(-2) (May 1986). To quantify the transfer of (137)Cs and (90)Sr from vegetation to milk in these seminatural conditions nine seasonally grazed alps were identified and vegetation and milk sampled during summer 2002 and summer 2003. Mean+/-SD milk transfer coefficients (fm) for (137)Cs and (90)Sr were 0.0071+/-0.0009 d l(-1), and 0.0011+/-0.0004 d l(-1), respectively; which for (137)Cs is markedly higher than those fm values found in intensive agricultural systems. Transfer kinetics for (137)Cs into cow milk were approximated using a 2-compartment model with a short and a long-term component. Fitting the model to empirical data results in reliable estimates of the time constant of the short-term component, biological half-life 1.06+/-0.28 d, whereas the estimates of the long-term component are subject to high uncertainties.

Radionuclide content in soils from four locations in a tropical rainforest near Golfito in Southern Costa Rica was investigated. For comparison, two nearby locations in open grassland were also studied. From each site 5 soil cores down to a depth of 15 cm were taken. The median contamination with 137Cs was 584 Bq m-2 (reference date 1 January 1996) and the coefficient of variation (CV) was 50%. This contamination can be attributed to global fallout from atmospheric nuclear weapon tests between 1945 and 1980. The mean contamination is slightly lower than the value expected for the latitude (8 degrees 42': 700 Bq m-2), which may be explained by migration of radiocaesium to subsoil below 15 cm or by uptake into the living biomass. Out of the total variability of 50%, around 20% can be attributed to the sampling and measuring process uncertainties, thus leaving a 45% contribution of spatial variability. A significant difference between forest and meadow sites could be detected: the meadow sites showed lower radiocaesium soil inventories (median: 291 Bq m-2) than the forest sites (643 Bq m-2). This may be explained by the agricultural activities carried out on meadow sites which lead to an increased redistribution of caesium in the soil profile and therefore a larger fraction of the total 137Cs lying below 15 cm. Another reason for higher contamination levels under forest can be attributed to the high interception potential of dense tree canopies for dry deposition. Extrapolating the 137Cs concentration below the sampling horizon, i.e. accounting for the cut-off of the profiles by the sampling technique, results in an estimated mean of 710 Bq m-2 for the forest sites, which is very close to the expected figure. The mainly mineral part of the forest soil profiles was analysed for the 137Cs transport parameters, apparent convection velocity (v = 0.14 +/- 0.09 cm a-1) and apparent diffusion constant (D = 0.79 +/- 0.49 cm2 a-1). The maximum concentration can be found at 5.3 +/- 2.9 cm depth, the half-value depth being 7.4 +/- 1.3 cm. The mean 40K activity concentration was 175 Bq kg-1 dry matter (CV = 69%) and 226Ra and 228Ra concentrations of 9.90 Bq kg-1 (CV = 23%) and 7.93 Bq kg-1 (CV = 20%) have been found, respectively.

Traces of the radionuclide (207)Bi were identified in soil and cryoconite (glacier sediment) samples from Alpine regions of Austria. This nuclide has been produced in thermonuclear explosions mainly in the early 1960s and subsequently dispersed in the atmosphere. Activity concentrations up to 22 Bq/kg d.m. have been found. The ratio (207)Bi:(137)Cs(global fallout) equals (1.70+/-0.12)10(-3), which is in accordance with literature data. When low levels of (207)Bi are assessed by gamma spectrometry, corrections must be made for a gamma line produced in the lead shield by neutron activation due to cosmic neutrons.

In the mountainous “Hohe Tauern” region of Salzburg (Austria), milk samples have been collected in a long-term montitoring programme since 1988, at eight alpine sites used for extensive, seasonal stock farming. For this alpine environment with its acidic soils developed on silicate bedrock, high soil-to-plant transfer factors and long-lasting 137Cs contamination levels in milk—the main product of seasonal agriculture at elevated altitudes—are characteristic features. The decrease in 137Cs concentration in milk measured since 1988 turned out to be best described by one or two effective half-lives. For the period from 1993 to 2007, which can be modelled with one effective half-life for all sites, effective half-lives between 3.7 and 15.0 years (ecological half-lives: 4.3–29.9 years) were obtained. The effective half-life increases with mean altitude of the investigated graze pastures, probably due to reduced migration velocities of 137Cs and low 137Cs half-value depths of a few centimetres in the soil.