Das Projekt "Gutachten 'Ableitung von Threshold Values für Schwermetalle in Böden'" wird vom Umweltbundesamt gefördert und von Fraunhofer-Institut für Molekularbiologie und Angewandte Oekologie durchgeführt. In the EU, various threshold values for heavy metals exist that refer to soil protection. However, these values are different in each member state. To improve the discussion on a harmonization of soil threshold values a compilation of the existing information is required. The project aimed at: 1. The compilation of derivation procedures applied in various EU member states and some other countries 2. A compilation of the respective threshold values 3. The assessment of the values with respect to the procedure of derivation and protection levels 4. A compilation of methods/procedures considering the mobile content of metals 5. The derivation of conclusions/recommendations of threshold values based on the principles of leaching and the availability of heavy metals. The compilation shows that in the countries included in the study different derivation procedures and protection levels are applied. The resulting threshold values may differ significantly. The current risk assessment is generally based on the total amount of contaminants in soil. It is, however, well-known that considering the total concentration is inadequate for assessing the environmental risk. Soil assessments based on available fractions are by far the more realistic and target-oriented procedures. To overcome this problem, some countries distinguish between different threshold values taking into account various pH-ranges, soil types and Corg-contents. The derivation of threshold values might be significantly approved by taking into account current knowledge on the more comprehensive parameter 'availability . At present international expert groups investigate the resorption of metals by humans and animals, the simulation of plant uptake, the availability for soil organisms and for micro-organisms with respect to degradation. Furthermore, leaching with regard to groundwater protection is regarded. A strategy for the derivation of soil values on the basis of available heavy metal concentrations is proposed