Chromium(III) -- chromium(VI) interconversions in seawater

The stable form of dissolved chromium in oxygenated seawater is Cr(VI). But Cr(III)-species are also present at an analytically significant level. It is shown that Cr(III) is oxidized only slowly by dissolved oxygen, and that manganese oxide is a strong catalyst for such oxidation. However, the low oceanic concentration of suspended MnO2 impedes the conclusion that the former process is quantitatively less important than the latter one. The distribution of dissolved chromium among Cr(VI)- and Cr(III)-species is probably kinetically controlled