Fig. 3. Redox potentials in soil columns (referenced to the standard H electrode). Symbols denote average redox potentials in the +0, +800, and +4000 mg L^-1 organic carbon (OC)–amended columns, and bars denote ranges encompassed by ±2 standard deviations. No +4000 mg L^-1 OC treatment was included in the control [no Cr(VI)] soils. The cases where lactate served as the OC treatment are indicated by an "L" next to the data. Also shown are ranges of redox potentials associated with Cr(VI)–Cr(III), Mn(IV)–Mn(II), Fe(III)–Fe(II), and S(VI)–S(-II) transformations.