ACID VOLATILE SULFIDES OXIDATION AND METALS (Mn, Zn) RELEASE UPON SEDIMENT RESUSPENSION: LABORATORY EXPERIMENT AND MODEL DEVELOPMENT

Sediment from the Anacostia River (Washington, DC, USA) was suspended in aerobic artificial river water for 14 d to investigate the dynamics of dissolved metals release and related parameters including pH, acid volatile sulfides (AVS), and dissolved/solid phase Fe2+. To better understand and predict the underlying processes, a mathematical model is developed considering oxidation of reduced species, dissolution of minerals, pH changes, and pH-dependent metals' sorption to sediment. Oxidation rate constants of elemental sulfur and zinc sulfide, and a dissolution rate constant of carbonate minerals, were adjusted to fit observations. The proposed model and parameters were then applied, without further calibration, to literature-reported experimental observations of resuspension in an acid sulfate soil collected in a coastal flood plain. The model provided a good description of the dynamics of AVS, Fe2+, S-(s)(0), pH, dissolved carbonates concentrations, and the release of Ca-(aq), Mg-(aq), and Zn-(aq) in both sediments. Accurate predictions of Mn-(aq) release required adjustment of sorption partitioning coefficient, presumably due to the presence of Mn scavenging by phases not accounted for in the model. The oxidation of AVS (and the resulting release of sulfide-bound metals) was consistent with a two-step process, a relatively rapid AVS oxidation to elemental sulfur (S-(s)(0)) and a slow oxidation of S-(s)(0) to SO4 (2-)((aq)), with an associated decrease in pH from neutral to acidic conditions. This acidification was the dominant factor for the release of metals into the aqueous phase. Environ. Toxicol. Chem. 2011:30:564-575. (C) 2011 SETAC