Boris Dehandschutter

The Red Mud Accident in Ajka (Hungary): Plant Toxicity and Trace Metal Bioavailability in Red Mud Contaminated Soil

The red mud accident of October 4, 2010, in Ajka (Hungary) contaminated a vast area with caustic, saline red mud (pH 12) that contains several toxic trace metals above soil limits. Red mud was characterized and its toxicity for plants was measured to evaluate the soil contamination risks. Red mud radioactivity (e.g., (238)U) is about 10-fold above soil background and previous assessments revealed that radiation risk is limited to indoor radon. The plant toxicity and trace metal availability was tested with mixtures of this red mud and a local noncontaminated soil up to a 16% dry weight fraction. Increasing red mud applications increased soil pH to maximally 8.3 and soil solution EC to 12 dS m(-1). Shoot yield of barley seedlings was affected by 25% at 5% red mud in soil and above. Red mud increased shoot Cu, Cr, Fe, and Ni concentrations; however, none of these exceed toxic limits reported elsewhere. Moreover, NaOH amended reference treatments showed similar yield reductions and similar changes in shoot composition. Foliar diagnostics suggest that Na (>1% in affected plants) is the prime cause of growth effects in red mud and in corresponding NaOH amended soils. Shoot Cd and Pb concentrations decreased by increasing applications or were unaffected. Leaching amended soils (3 pore volumes) did not completely remove the Na injury, likely because soil structure was deteriorated. The foliar composition and the NaOH reference experiment allow concluding that the Na salinity, not the trace metal contamination, is the main concern for this red mud in soil.

Multi-method chronometry of the Teletskoye graben and its basement, Siberian Altai Mountains: new insights on its thermo-tectonic evolution

Abstract The Altai Mountains form an intracontinental, transpressive deformation belt in the NW Central Asian orogenic system. Using a multi-method chronometric approach, the thermo-tectonic history of the basement underlying the Teletskoye graben area is constrained in more detail. The results provide new insights into the Siberian Altai basement evolution from the Early Palaeozoic to the present. Zircon SHRIMP (sensitive high-resolution ion microprobe) U–Pb ages (Late Ordovician–Early Silurian, 460–420 Ma) indicate an earlier crystallization age for the basement granitoids than previously thought (Late Devonian–Early Carboniferous, 370–350 Ma), while new multi-mineral 40Ar/39Ar age spectra suggest continuous basement cooling throughout the Devonian–Carboniferous. Reactivation of long-lived Palaeozoic structures controls the Teletskoye graben formation since the Plio-Pleistocene as a distant effect of India–Eurasian convergence. Deformation is propagated through Central Asia and Siberia along an inherited structural network closely associated with its basement fabric. A similar reactivation affected the Altai during the Mesozoic. Modelled apatite fission-track data suggest Late Jurassic–Cretaceous (150–80 Ma) cooling, interpreted to be related to denudation and the tectonic reactivation that we link to the coeval Mongol–Okhotsk orogeny. From the Late Cretaceous until the Pliocene, the thermal history models indicate a period of stability. Roughly around 5 Ma ago renewed cooling is observed that possibly represents the denudation and growth of the present-day Altai, and provides the context for the Teletskoye graben formation. A modelled Late Cenozoic cooling can be a result of, or overemphasized by, a modelling artefact. Some caution should be taken not to overinterpret this cooling phase.

Recent strike-slip deformation of the northern Tien Shan

Abstract The paper presents a geodynamic interpretation of the deep structure and active tectonics of the northern Tien Shan, with particular emphasis on strike-slip motions, which produced a pull-apart in the centre of the Issyk-Kul basin. The study is based on a detailed interpretation of satellite imagery, fault plane solutions of earthquakes, seismic, and geodetic data. Seismic and magnetotelluric studies show tectonic layering of the Tien Shan lithosphere, with several nearly horizontal viscoelastic layers and the lower layer underthrust northward in the northern Tien Shan. This active process may be responsible for the intricate present-day tectonic framework of the northern Tien Shan. The recent tectonics of the northern Tien Shan inherits the earlier structure: The lens-shaped Issyk-Kul microcontinent comprising Precambrian-Palaeozoic metamorphic and magmatic rocks is surrounded by thick shear zones which have been involved in the activity over most of the Cenozoic. In the Quaternary the strain propagated as far as the central part of the Issyk-Kul basin.

Estimating the terrestrial gamma dose rate by decomposition of the ambient dose equivalent rate

An extensive network of dose rate monitoring stations continuously measures ambient dose rate across Europe, as part of the EURDEP system. Its purpose is early warning in radiological emergencies and documenting its temporal and spatial evolution. In normal conditions, when there is no contribution to the dose rate signal coming from fresh anthropogenic contamination, the data represent the radiation background, i.e. the combined natural radiation and existing anthropogenic contamination (by global and Chernobyl fallout). These data are being stored, but have so far not been evaluated in depth, or used for any purpose. In the framework of the EU project European Atlas of Natural Radiation the idea has emerged to exploit these data for generating a map of natural terrestrial gamma radiation. This component contributes to the total radiation exposure and knowing its geographical distribution can help establishing local radiation budgets. A further use could be found in terrestrial dose rate as a proxy of the geogenic radon potential, as both quantities are related by partly the same source, namely uranium content of the ground. In this paper, we describe in detail the composition of the ambient dose equivalent rate as measured by the EURDEP monitors with respect to its physical nature and to its sources in the environment. We propose and compare methods to recover the terrestrial component from the gross signal. This requires detailed knowledge of detector response. We consider the probes used in the Austrian, Belgian and German dose rate networks, which are the respective national networks supplying data to EURDEP. It will be shown that although considerable progress has been made in understanding the dose rate signals, there is still space for improvement in terms of modelling and model parameters. An indispensable condition for success of the endeavour to establish a Europe-wide map of terrestrial dose rate background is progress in harmonising the European dose rate monitoring network.

Volumetric matrix strain related to intraformational faulting in argillaceous sediments

Soft-sediment deformation involves complex interactions between discrete fracturing and diffuse bulk strain, described in terms of volume change and shear strain in a critical state mechanics framework. This study reports on a mesoscale normal fault zone, intraformational in Oligocene argillaceous sediments from the Boom Formation (Belgium), containing several metre-scale normal fault strands. They form either discrete fault planes or decimetre-wide shear zones with internal fabric. The faults have been subjected to microtectonic and petrophysical analysis. Small but significant changes occur in the porous network of the argillaceous matrix approaching a fault or shear zone, indicating compactional strain in both footwall and hanging wall. Internal compaction associated with faulting is put forward as a ductile–brittle feedback mechanism in the kinematics of intraformational fracture systems. Small differential stress induced by compaction and minor regional tectonic forces (differential uplift and tilt) and subsequent gravitational forces (downslope shear stress) induce small shear bands in nearly critically stressed weak mud. Shear banding is accompanied by layer-parallel shortening and bulk volume loss. This provides an additional extension of endogenous origin, accommodated by further deformation. This ductile–brittle feedback mechanism eventually leads to commonly observed intraformational collapse structures called polygonal fault systems.

Homogenity of geological units with respect to the radon risk in the Walloon region of Belgium

In the process of mapping indoor radon risk, an important step is to define geological units well-correlated with indoor radon. The present paper examines this question for the Walloon region of Belgium, using a database of more than 18,000 indoor radon measurements. With a few exceptions like the Carboniferous (to be divided into Tournaisian, Visean and Namurian-Westphalian) and the Tertiary (in which all Series may be treated together), the Series/Epoch stratigraphic level is found to be the most appropriate geological unit to classify the radon risk. A further division according to the geological massif or region is necessary to define units with a reasonable uniformity of the radon risk. In particular, Paleozoic series from Cambrian to Devonian show strong differences between different massifs. Local hot-spots are also observed in the Brabant massif. Finally, 35 geological units are defined according to their radon risk, 6 of which still present a clear weak homogeneity. In the case of 4 of these units (Jurassic, Middle Devonian of Condroz and of Fagne-Famenne, Ordovician of the Stavelot massif) homogeneity is moderate, but the data are strongly inhomogeneous for Visean in Condroz and in the Brabant massif. The 35 geological units are used in an ANOVA analysis, to evaluate the part of indoor radon variability which can be attributed to geology. The result (15.4-17.7%) agrees with the values observed in the UK.

Mapping uranium concentration in soil: Belgian experience towards a European map

A map of uranium concentration in soil has been planned for the European Atlas of Natural Radiation. This Atlas is being developed by the Radioactivity Environmental Monitoring (REM) group of the Joint Research Centre (JRC) of the European Commission. The great interest in uranium compared to other terrestrial radionuclides stems from the fact that radon (222Rn) is in the decay chain of uranium (238U) and that public exposure to natural ionizing radiation is largely due to indoor radon. With several different databases available, including data (albeit not calibrated) from an airborne survey, Belgium is a favourable case for exploring the methodology of uranium mapping. A harmonized database of uranium in soil was built by merging radiological (not airborne) and geochemical data. Using this harmonized database it was possible to calibrate the data from the airborne survey. Several methods were used to perform spatial interpolation and to smooth the data: moving average without constraint, by soil class and by geological unit. When using the harmonized database, it is first necessary to evaluate the uranium concentration in areas without data or with an insufficient number of data points. Overall, there is a reasonable agreement between the maps on a 1xa0kmxa0×xa01xa0km grid obtained with the two datasets (airborne U and harmonized soil U) with all the methods. The agreement is better when the maps are reduced to a 10xa0kmxa0×xa010xa0km grid; the latter could be used for the European map of uranium concentration in soil.

Statistical analysis of indoor radon data for the Walloon region (Belgium)

Two databases of indoor radon measurements in the Walloon region in Belgium can be used to establish a radon risk map of this region, taking into account the geological information. The data were collected, respectively, by long-term track-etch measurements and by short-term charcoal measurements. Here we present a preliminary study showing that the two databases can be merged. We begin our study by testing two types of distributions: the log-normal distribution and the log-Gumbel distribution, with the purpose of selecting the best to fit our databases. The paper then describes a methodology that allows us to combine them. The composite database will be used to establish a radon risk map for the Walloon region based on geology.

High radon areas in the Walloon region of Belgium

Indoor radon data from Southern Belgium are organised in 35 geological units (GUs), most of which are homogeneous with respect to the radon risk. The percentage of cases above the reference level (400 Bq m(-3); 300 Bq m(-3) in the future) is calculated for these GUs from the observations and from the log-normal distribution fitted to the data. Affected areas are defined as areas with more than 1 % of houses above the reference level. In the north of the region, the old Palaeozoic basement is generally covered by Silesian, Cretaceous and Tertiary rocks, which are unaffected. The affected areas here are hot spots associated with specific Palaeozoic outcrops. In the south, there is generally no cover above Palaeozoic formations, which are often radon affected. The affected areas of Ardenne and Condroz dominate this part, but unaffected areas occur like Famenne and Gaume. About 48 % of the Walloon region is expected to be radon affected.

Mapping potassium and thorium concentrations in Belgian soils

The European Atlas of Natural Radiation developed by the Joint Research Centre (JRC) of the European Commission includes maps of potassium K and thorium Th. With several different databases available, including data (albeit not calibrated) from an airborne survey, Belgium is a favourable case for exploring the methodology of mapping for these natural radionuclides. Harmonized databases of potassium and thorium in soil were built by radiological (not airborne) and geochemical data. Using this harmonized database it was possible to calibrate the data from the airborne survey. Several methods were used to perform spatial interpolation and to smooth the data: moving average (MA) without constraint, or constrained by soil class and by geological unit. Overall, there was a reasonable agreement between the maps on a 1u202f×u202f1u202fkm2 grid obtained with the two datasets (airborne data and harmonized soil data) with all the methods. The agreement was better when the maps are reduced to a 10u202fkmu202f×u202f10u202fkm grid used for the European Atlas of Natural Radiation. The best agreement was observed with the MA constrained by geological unit.