Evidence for groundwater contamination by heavy metals through soil passage under acidifying conditions

The research reported here is aimed at improving the knowledge of the mobility of the heavy metals cadmium and zinc in vulnerable soil types. We use the term vulnerable with reference to vulnerability of groundwater for contamination by soil leaching. At diffuse soil immissions of heavy metals, accumulation is often supposed to occur mainly in the topsoil. Binding of heavy metals in this soil compartment is relatively strong, because of de presence of soil organic matter, clay-minerals and sesquioxides. If soil contains little organic matter and no clay minerals a reduced accumulation in the topsoil and an increased leaching of heavy metals to the groundwater is expected. Also the pH of the soil is of influence on this leaching. Cadmium contamination of the environment has drawn attention since the sixties. The most important occasion was an environmental calamity in Japan where rice paddy was irrigated by cadmium contaminated river water. The pollution was originated from an upstream situated mine. Also in the Netherlands concern exists about pollution of the environment by cadmium. Especially in the Dutch-Belgian Kempen elevated cadmium contents are found in soils and plants, as a result of industrial pollution. This study particulary addresses the questions whether or when the diffuse metal immissions breakthrough in the groundwater of the Kempen