As with Mo(VI), Ni(II), Pb(II), and Zn(II), Cr(III) and V(III) are stable in the presence of GRSO4 (i.e., not reduced) . Although no information is available on the interaction of Co(II) or Mn(II) with GR, reduction of either of these to lower valence states by GR is thermodynamically unfavorable. Therefore the moderate enhancement of CT reduction in the Cr(III)-, Mn(II)-, Mo(VI)-, Pb(II)-, and V(III)-amended systems does not involve reduction of these metals to zero-valent species.