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(67-05) Role of free metal ions and complexes in metal uptake by aquatic invertebrates and fish. Blust, R*,1, Lorenzo, J2, Mubiana, V1, Beiras, R2, Bervoets, L1, 1 Department of Biology, Antwerp, Belgium, Belgium2 Department of Ecology and Animal Biology, Vigo, Spain, Spain ABSTRACT- The uptake, accumulation and toxicity of metals to aquatic organisms strongly depends on the chemical speciation of the metals in the environment. Generally, metal uptake is poorly explained on a total metal concentration scale since this neglects the effects of metal complexation and other confounding factors on metal availability. To take into account the effect of metal complexation on metal availability, metal exposure is usually much better explained using a free metal ion activity scale. The use of this scale assumes that metal availability depends on the free metal ion in the solution. Numerous studies have indeed demonstrated that complexation decreases metal uptake and toxicity in a variety of aquatic organisms. Most of these experimental studies have used small organic and usually synthetic ligands to demonstrate the relationship between free metal ion activity and metal availability. Recent studies using natural organic matter have shown contrasting results. In some cases complexation decreased metal uptake while in other cases it increased metal uptake. Several explanations exist for these seemingly conflicting results. The metal-complexes formed are carried across the membrane by more or less specific transport systems. Some metal complexes may diffuse across the membrane by partitioning in the hydrocarbon carbon of the membrane. The metal complex may dissociate in the diffusion layer lining the membrane interface so that the free metal ion activity is actually higher than in the bulk solution. The metal complex may also act as a reservoir of free metal ions when the supply of free metal ions to the interface is slower than the removal from the interface by the internalisation step. In this study the role of these different processes in controlling metal uptake has been evaluated and a mechanistic framework is developed which describes the conditions under which the free ion activity model is no longer valid and metal complexes contribute significantly to metal uptake. Key words: metals, complexation, bioavailability, aquatic |
