Some theoretical aspects of stability and solubility of inorganic arsenic in the freshwater environment

The concentrations of some major and minor ionic constituents of different freshwater systems are listed, and “typical” concentration estimates are given for freshwater in general. Fourteen different metals are examined for a possible controlling influence on total dissolved arsenic in freshwater. Four metals (Ba, Cr, Fe, Cu) emerge as possible candidates, and are examined more closely. The total dissolved arsenic concentration allowed by each of these metal arsenates is shown as a function of pH when the metal ion activity itself is controlled by a relatively insoluble compound. Barium ion at a concentration typical for freshwater emerges as the most convincing candidate capable of holding total dissolved arsenic to rather low concentrations, while chromium and iron emerge as possibilities. A new E h-pH diagram for arsenic showing the relative stability domain for barium arsenate is presented in which the arsenic sulfide domains have been included and somewhat simplified and clarified.