Chemical Equilibrium Data Bases and Tools for Calculating Zinc Sulfide Geochemistry in Freshwater Sediments and its Toxicity

Abstract

Abstract This paper evaluates chemical modelling tools, thermodynamic equilibrium data, and field data appropriate for estimating the concentration of zinc and other relevant metals in freshwater sediments. To identify the expected primary zinc species, a literature search was completed which summarized the available knowledge. Within the available literature, the largest variability was found in the metal sulfide system. A critical review of the data, together with application of a consistent procedure for incorporating primary sulfide constants in a thermodynamic data base, was used to reduce the variation in the reported values for the solubility and complexation constants. The primary soluble forms of zinc, iron and lead for two field sites impacted by zinc discharges (Hamilton Harbour impacted by steel mill and treated urban wastewater discharges and a base metal mine impacted site) were ZnOHHS0, Fe2+ and Pb(HS)3, respectively. Implications of this work for the evaluation of aquatic toxicity in aquatic sediments are also presented. The chemical equilibrium model used in this study—solid phase speciation measurements—and a sediment phase mass balance model can form the basis for determining the toxicity status of a system due to zinc contamination.