PARENT SESSION

1E - Speciation of chemicals
Poster Hall
8:30 AM - Tuesday, 29 April 2003

(TUP/37) Modelling the equilibrium speciation of metals in solution with propagation of uncertainties.

Blust, Ronny¹, Van Ginneken, Luc¹, ¹ Department of Biology, University of Antwerp, Antwerp, Antwerp, Belgium

ABSTRACT- The distribution and bioavailability of metals in aquatic and terrestrial environments strongly depends on the chemical speciation of the metals. In general the behaviour and effects of metals are usually better explained by models that account for the effects of chemical speciation processes, compared to models that express effects on a total metal concentration scale. For this purpose a variety of models have been developed that can be used to calculate the chemical speciation of metals in complexing environments when the composition of the solution is known. The results of such calculations strongly depend on the completeness and correctness of the reactions and equilibrium constants describing the chemistry of the solution. A critical analysis of the equilibrium constants reported in scientific literature shows a large degree of variation and uncertainty in the constants being reported. For some reactions the equilibrium constants have been obtained rather accurately, but in many cases the values are rather uncertain. Nonetheless, most chemical speciation models do not account for the effects of the uncertainty associated to the equilibrium constants on the results generated by the model. To deal with this a speciation model has been developed that takes these uncertainties into account and generates model output that includes upper and lower concentration limits for the different species included. The model has been used to calculate the chemical speciation of a series of trace metals in freshwater and seawater environments and to show to what extend the uncertainties associated to the equilibrium reaction constants can influence the output. The results are used to set quality criteria for equilibrium reaction constants and provide guidelines for the selection of the best values from available data sets.

Key words: Speciation, Metals, Modelling, Uncertainty