DEGRADATION OF POLYCHLORINATED DIBENZO-P-DIOXIN AND DIBENZOFURAN CONTAMINANTS IN 2,4,5-T BY PHOTOASSISTED IRON-CATALYZED HYDROGEN-PEROXIDE

The objective of this study was to determine the fate of polychlorinated dibenzo-p-dioxin (PCDD) and dibenzofuran (PCDF) contaminants in the herbicide 2,4,5-trichlorophenoxyacetic acid after treatment by photoassisted Fe3+-catalyzed hydrogen peroxide oxidation, which is being investigated for waste treatment. Toluene-extraction of aqueous reagent grade 2,4,5-T gave 30 quantifiable PCDD/F isomer peaks, some of which represented more than one congener. They included 13 tetra- through heptachloro PCDDs totalling 18.4 ng/g, and 17 tetra- through octachloro PCDFs totalling 12.9 ng/g. Treatment with Fe3+/H2O2/hv (mole ratio 2,4,5-T: Fe3+: H2O2 = 1: 10: 200; visible fluorescent light, 300 nm cutoff) in aerated solution at pH 2.8 resulted in 89-100% removal of all PCDD/F peaks except that for OCDF, which was 66% removed. The 2,4,5-T was shown previously to be completely mineralised to HCl and CO2. Direct photolysis of the PCDD/Fs was negligible. The 2,3,7,8-tetra-CDD referenced ''toxic equivalent'' used in risk assessment was reduced by 99.9% (U.S. Environmental Protection Agency `method) or 99.6% (international method). Reaction mixtures supplemented with 2,3,7,8-(UL-C-14)-tetra-CDD and 2,3,4,7,8-(dichlorophenyl-C-14)-penta-CDF evolved up to 45 and 64%, respectively, theoretical yield of (CO2)-C-14. Most of the remaining C-14 was converted to hydrophilic forms not extractable by toluene. Dark (Fe3+/H2O2) treatment was somewhat less effective overall.