This request fits within the framework of a study dealing with the bioavailability and ecotoxicological effects of heavin metals for different biota. The following objectives are being put forward : 1) the identification and the determination of the relative importance of the modifying factors influencing metal toxicity. 2) the determination of adaptation-, tolerance limits of different biota for essential metals (Cu, Zn,..3) establishment of dose effect relationships (critical body concentrations) of different metals for different types of biota.