Abstract: tThis work assesses the influence of the operating conditions H2O2dose (20 or 100% of the stoichiometricamount), temperature (20 or 70?C), and the presence of chloride in the oxidation medium in the for-mation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) during Fenton treatment ofaqueous samples of 2-chlorophenol, 2-CP, one of the strongest precursor of PCDD/Fs. After 4 h of oxida-tion in the experiments carried out with 20% H2O2chlorinated phenoxyphenols and biphenyls, whichare intermediates in PCDD/Fs formation, as well as PCDD/Fs were observed, resulting in concentrations11 times higher than in the untreated sample. Additionally, when NaCl was also present in the reactionmedium, PCDD/Fs were formed at higher extent, with a total concentration 74.4 times higher than inthe untreated 2-CP solution. Results depicted a preferential formation of PCDFs over PCDDs, with domi-nance of lower chlorinated PCDD/Fs (tetra and penta-PCDD/Fs). Besides, the formation of the most toxicPCDD/Fs congeners (2,3,7,8-PCDD/Fs) was not favored under the operating conditions used in this work.

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