Alecos Demetriades

The IUGS/IAGC Global Geochemical Baseline Programme aims to establish a global geochemical reference baseline for >60 determints in a range of media for environmental and other applications. The European contribution to the programme has been carried out by government institutions from 26 countries under the auspices of the Forum of European Geological Surveys (FOREGS). The main objectives of this European survey were: 1) to applay standardised methods of sampling, chemicval analysis and data managment to prepare a geochemical baseline across Europe ; and 2) to use this reference network to level national baseline datasets. Samples of stream water, stream sediment and three types of soil (organic top layer, minerogenic top and sub soil) have been collected at 900 stations, each representing a catchment area of 100 km2, corresponding to a sampling density of about one sample per 4700 km2. In addition, the uppermost 25 cm of floodplain sediment was sampled from 790 sites each representing a catchment area of 1000 km2. All soil and sediment samples were prepared at the same laboratory, and all samples of particular sample types were analysed by the same method at the same laboratory. More than 50 elements, both total and aqua regia extractable concentrations, and other parameters (such pH and grain size) were determined on the <2 mm grain size fraction of soil and floodplain sediment samples and on the <0.15 mm grain size fraction of stream sediment samples, and total concentrations of organic soil samples were measured after using a strong acid digestion. Nine laboratories of European geological surveys carried out the analytical work. Altogether, 360 geochemical maps showing the distribution of elements across Europe have been prepared. All the results and field observations are organised in a common database and the maps are published as a Geochemical Atlas of Europe. All the sampling sites were photographed and this photo archive is also available. Samples have been archived in the Slovak Republic for possible future use. Initial results show that the distribution patterns of both water and solid samples are related to such factors as large-scale tectonic provinces, geochemical variations of large lithological units, extension of the Weichselian glaciation, and contamination reflecting industrialized areas and regions of intensive agriculture.

Multi-media and multi-element geochemical survey carried over almost the whole of Europe indicate that baseline concentrations of chemical elements in samples of soil, humus, stream water and sediments (stream and floodplain) vary spatially by up to several orders of magnitude, because of geological, climatic and other factors, including inputs from different human actvities. The EuroGeoSurveys-FOREGS geochemical baseline project provides European decision-makers with data about the chemical comopsition of the near-surface environment at the end of the twentieth century. It is the „ baseline“ against which the next generation will quantify changes, whether natural or human-made. Although the sampling density used in the current project is low, approximately one sample site per five thousend square kolimetars (1 site/5000 km2), geochemists have been using quite effectively such low-sample density survey to cover large areas for the last forty years. This geochemical baseline survey provides us with invaluable information about the natural and human-induced concentrations of chemical elements in materials of the near-surface environment, where we live on, grow our crops, raise our livestock, and from which we extract our drinking water, and other raw materials, including mineral wealth. Our quality of life depends on the chemical composition of water (river or groundwater) and soil, whether residual (developed directly on bedrock) or alluvial (transported by river water and deposited during flood episodes on floodplains). The geochemical distribution maps show distinct geographical differences in the levels of potentially harmful elements from natural geogenic sources, includig lithology and mineralisation, and from natural processes such as climate, which influence the original levels. This geochemical variatin illustrates the difficulty in defining a single guidline value for „ water“ , „ soil“ and „ sediment“ to be applied all over Europe. Finally, the geochemical maps could be used to identify potential geohazard and geohealth risks for more detailed investigations.