Controls on Mn, Fe, Co, Ni, Cu, and Zn Concentrations in Soils and Water: the Significant Role of Hydrous Mn and Fe Oxides

Abstract

It is proposed that the hydrous oxides of Mn and Fe, in general, furnish the principal control on the fixation of Co, Ni, Cu, and Zn (heavy metals) in soils and fresh water sediments; hydrous oxides of Mn and Fe are nearly ubiquitous in clays, soils, and sediments. The common occurrence of these oxides as coatings allows the oxides to exert chemical activity far out of proportion to their total concentrations. Sorption or desorption of these heavy metals occurs in response to the following factors: (1) aqueous concentration of the metal in question; (2) aqueous concentration of other heavy metals; (3) pH; and (4) amount and strength of organic chelates and inorganic complex ion formers present in solution. Other suggested controls on the concentration of the heavy metals in soils and fresh waters are: (1) organic matter; (2) clays; (3) carbonates; and (4) precipitation as the discrete oxide or hydroxide. The available information on these controls is reviewed and found to be inadequate to explain the fixation of Co, Ni, Cu, and Zn.