REDUCTIVE DEHALOGENATION OF HEXACHLORETHANE, CARBON-TETRACHLORIDE, AND BROMOFORM BY ANTHRAHYDROQUINONE DISULFONATE AND HUMIC-ACID

The reductive dehalogenation of hexachloroethane (C2Cl6), carbon tetrachloride (CCl4), and bromoform (CHBr3) was examined at 50-degrees-C in aqueous solutions containing either (1) 500 muM of 2,6-anthrahydroquinone disulfonate (AHQDS), (2) 250 muM Fe2+, or (3) 250 muM HS-. The pH ranged from 4.5 to 11.5 for AHQDS solutions and was 7.2 in the Fe2+ solutions and 7.8 in the HS- solutions. The observed disappearance of C2Cl6 in the presence of AHQDS was pseudo-first-order and fit k'(CCl4) = k0[A(OH)2] + k1[A(OH)O-] + k2[A(O)2(2-)] where A(OH)2, A(OH)O-, and A(O)2(2-) represent the concentrations of the three forms of the AHQDS in solution. The values of k0, k1, and k2 were approximately 0, 0.031, and 0.24 M-1 s-1, respectively. The addition of 25 mg of C/L of humic acid or organic matter extracted from Borden aquifer solids to aqueous solutions containing 250 muM HS- or Fe2+ increased the reduction rate by factors of up to 10. The logarithms of the rate constants for the disappearance of C2Cl6 and CCl4 in seven different experimental systems were significantly correlated; log k'(CCl4) = 0.64 log k'(C2Cl6) - 0.83 with r2 = 0.80. The observed trend in reaction rates of C2Cl6 > CCl4 > CHBr3 is consistent with a decreasing trend in one-electron reduction potentials.