• Flyer


• Workshop report of the organizers
   

Kurzbeschreibung und Folien der Hauptvorträge des Workshops/abstracts and presentations of the workshop

Ms. Wiebke Drost (UBA) presented the concepts of the tiered approach taking metal bioavailability into account. It was stated that bioavailability is an important issue, because it would be an improvement for the hazard assessment to know how much of the toxicant is taken up from the different environmental phases. However, it is not clear cut which of the abiotic and biotic parameters determine the bioavailability. The guidance for metal risk assessment under REACH suggests a tiered approach which was briefly introduced. This concept considers the free ionic form of the metals to be the most bioavailable form. Depending on whether a risk has been identified or not, availability of physico-chemical data and availability of a speciation model or Biotic Ligand Model for the metal regarded an adequate tier-level has to be selected . The free metal ion concentration is considered the as the most relevant form for uptake. However apart from geochemical conditions which control free metal concentration, bioavailability is additionally a result of contaminant/particle interaction and can be superimposed by organisms' activity. Hence, the question arises whether this tiered approach indeed reduces the uncertainty or do new uncertainties emerge?

• Taking metal bioavailability into account - The concepts of the tiered approach

Mr. Wolfgang Ahlf (TUHH) presented the need of knowing, in relation to metal bioavailability, the main uptake routes of different organisms in aquatic systems. Generally, it is considered that for most trace metals the free metal ions have the highest bioavailability . Thus, the presence of the hydrophilic complexing agent EDTA in water reduces the equilibrium concentration of metal ions with a corresponding decrease in the metal uptake. In the presentation data from experiments were shown which confirm this assumption. However, aquatic systems are dynamic and there is continuous interaction between solid phases (sediment, suspended matter) and liquid phases (freshwater, pore water). Transfers of metals between solid phases are regular processes, due to non-equilibrium situations.
 
The biotic ligand model (BLM) approach has been proposed for use in European Union (EU) risk assessments. The BLM provides a means to predict ecotoxicological effect of metals in the environment, but at present assumes that the most significant uptake is from the dissolved phase. Asking for the relevant exposure pathways for inorganic metals to organisms, the compartments water and sediment have been evaluated and in addition the importance of contaminated food. There is evidence in literature, that uptake occurs via the dissolved phase, metal complexes, dietary and particle-bound metals. It is apparent that dietary accumulation of metals is at least as important as metal uptake from the aqueous phase and in many cases dominates metal accumulation.

• Metal Bioavailability - critical aspects

• Consideration of bioavailability in regulation, requirements and consequences

Kurzstatements der Teilnehmer/short-statements of participants