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 trea tment. Seepage water of refuse dumps contains, besides other organic c ompounds, high concentrations of pentachlorophenol (PCP) and tetrachlo rophenols (TCP). During the UV irradiation of PCP-containing water sam ples, the formation of polychlorinated dibenzo-p-dioxins (PCDD) and po lychlorinated dibenzofurans (PCDF) is possible. The toxicity equivalen ce value (TEQ) of the PCDDs/PCDFs increased in an irradiated solution containing purified PCP about by a factor of 150. In samples of techni cal PCP and seepage water with high TEQ, we found a decrease of the TE Q 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 dibe nzo-p-dioxins and heptachlorinated dibenzofurans were formed by the co ndensation of PCP and TCPs, which were decomposition products of PCP, and the photochemical decomposition of octachlorodibenzo-p-dioxin (OCD D). The ratios of the formed heptachlorinated congeners point to a spe cial decomposition way of the OCDD and OCDF in irradiated water sample s. OCDD preferently loses a chlorine atom in the peri-position (positi ons 1, 4, 6, and 9). OCDF preferently loses a chlorine atom only in th e peri-position next to the C-C bridge (positions 1 and 9).