PW13 Metals in the Environment: Regulatory and Risk Concerns
Exhibit Hall
8:00 AM - Wednesday
(PW233) Strengths and limitations of biotic ligand models to predict metal toxicity.
Blust, R1, 1 Department of Biology, University of Antwerp, Antwerp, Antwerp, Belgium
ABSTRACT- The toxicity of metals to aquatic and terrestrial organisms depends on a variety of processes of which the physical and chemical speciation of the metals in the environment and the physiological organisation of the organisms are the most important. Metal uptake, accumulation and toxicity vary orders of magnitude, both among species and among environments. These differences in metal sensitivity are related to differences in the bioavailability, accumulation kinetics and cellular processing of the metals. To derive safe and meaningful environmental quality criteria for metals it is important to understand how these processes influence metal toxicity at the individual and higher levels of organisation. Within this framework the effects of environmental exposure conditions on metal availability has received considerable attention and one of the outcomes has been the development of so called Biotic Ligand Models for metal toxicity. These models express metal toxicity in terms of the binding of the metal to a biological ligand on the exchange surfaces or inside the organism assuming equilibrium conditions. The model takes into account metal availability by accounting for differences in chemical speciation and competition among major and minor cations for binding sites. So far most of these models have only considered relatively simple acute toxicity exposure scenarios, but also models for chronic toxicity are being developed. Results available so far show that there are important differences between the acute and chronic models in terms of the parameters driving the models. One of the reasons is that the equilibrium assumptions underlying the models largely neglect the dynamic nature of metal exposure and toxicity relationships. Another limitation is the lack of physiological realism of most biotic ligand models developed so far, i.e. what do the biotic ligand binding constant really mean. To address these issues the current work assesses the concepts underlying the biotic ligand model in terms of current understanding of the processes driving metal availability, accumulation and toxicity. It is explored to what extend these mechanistic concepts are incorporated in the biotic ligand models and to what extend the assumptions underlying the models are a correct translation of what is really going on.
Key words: bioavailability, metals, toxicity, blm