Chromium: Sources, Speciation, Toxicity, and Chemistry

Abstract

In the environment, chromium is found almost exclusively in the trivalent, 3+, and hexavalent, 6+, oxidation states. Chromium3+ is stable in the presence of water and air; however, chromium6+ as chromate is kinetically stable, but thermodynamically unstable. Chromium has a range of effects in living organisms. In plants, as will be the focus of the following chapters of this work, chromium is a toxin as either Cr3+ or Cr6+. In animals, the status has been highly debated since the element as the trivalent ion was first proposed as an essential element about seventy years ago; however, the element is no longer considered to be essential but may have beneficial pharmacological effects. The modes of Cr3+ transport in animals has recently been elucidated and may provide insight on how the metal ion can be transported in plants. Chromate is toxic and carcinogenic. A focus of the chapter will be on techniques to characterize chromium in mammals in terms of structure and potential function to suggest how the methods cold be extended to plants.