Ministries have each their own models to assess risks of chemicals. This report gives an overview of models used in environmental policy to asses risks on ecosystems. Nowadays, many locations deal with contamination that exceeds the risk limits. It therefore becomes crucial for environmental policy to determine real ecological risks of diffuse and chronic stress caused by single contaminants and by mixtures thereof. Effects of diffuse, chronic stressors are difficult to identify in the field. These issues triggered the development of the Stimulation Program Systems-Oriented Ecotoxicological Research (SSEO). Within the SSEO program, data are collected from diffuse and chronic contaminated fields. These data will be used in the next research phase to validate the eco(toxico)logical models used for policy formulation. The validation of models gives insight on the fact if policy measures should be (partially) intensified or relaxed for reaching the environmental policy targets.