In this project, we will study the effect of soil properties on the availability and toxicity of nickel in soils. Sixteen soils, representative for the major soil types in Europe, were selected and sampled. These soils are contaminated in the lab with nickel and the toxicity for soil microbial processes (nitrification and substrate induced respiration) will be derived. The results will be used to develop an empirical relationship of toxicity as a function of soil bioavailability parameters. The effect of aging reactions on the bioavailability and toxicity of nickel will also be studied during 18 months after contamination. Finally results for all these lab-contaminated soil samples will be compared with results for nickel contaminated field samples.