Formation of Polychlorinated Dibenzo-p-dioxins and Polychlorinated Dibenzofurans during the Photolysis of Pentachlorophenol-Containing Water

Purification of seepage water or wastewater by UV irradiation for the destruction of organic impurities is an upcoming method for water treatment. Seepage water of refuse dumps contains, besides other organic compounds, high concentrations of pentachlorophenol (PCP) and tetrachlorophenols (TCP). During the UV irradiation of PCP-containing water samples, the formation of polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF) is possible. The toxicity equivalence value (TEQ) of the PCDDs/PCDFs increased in an irradiated solution containing purified PCP about by a factor of 150. In samples of technical PCP and seepage water with high TEQ, we found a decrease of the TEQ value, for example, the TEQ of 1931.0 pg/L of PCDD in technical PCP is reduced to 99,0 pg/L. During the irradiation, heptachlorinated dibenzo-p-dioxins and heptachlorinated dibenzofurans were formed by the condensation of PCP and TCPs, which were decomposition products of PCP, and the photochemical decomposition of octachlorodibenzo-p-dioxin (OCDD). The ratios of the formed heptachlorinated congeners point to a special decomposition way of the OCDD and OCDF in irradiated water samples. OCDD preferently loses a chlorine atom in the peri-position (positions 1, 4, 6, and 9). OCDF preferently loses a chlorine atom only in the peri-position next to the C‒C bridge (positions 1 and 9).