A lot of marine environmental problems emerge due to disposal of harmful substances (e.g. heavy metals, polycyclic aromatic hydrocarbons, halogenated hydrocarbons etc.). Regarding political purposes the disposals have to be validated for measurements of decontamination and protection of environment. The practical problems of validation regarding standard and marginal values are profound. Standard values are set up on different combinations for single substances or classes of substances. In most cases they are orientated on the toxicity of the substance or a "natural background level" of concentration. Usually an ecosystem or its compartments are not contaminated with only one, but with a combination of different substances. The valuation of such a cocktail is connected with difficulties as explained in the following example: