Photodegradation of polychlorinated dibenzo-p-dioxins and dibenzofurans in aqueous solutions and in organic solvents

Quantitative structure–property relationships (QSPRs) on direct photolysis of PCDDs

“…The study of Kim and O'Keefe (2000) supported the explanation. They found that at 300 nm 2,7-D 2 CDD and 1,2,7,8-T 4 CDD had higher ®rst-order photodegradation rate constants in 60% acetonitrile/water than in pure water, and the solvent e ect was reversed for 2,7-D 2 CDF and 1,2,7,8-T 4 CDF.…”

“…According to their explanation, PCDFs have only one oxygen atom, they are more polarized than PCDDs and they could be more reactive in pure water than in less polar solutions such as 60% acetonitrile/water. It was proposed from previous studies (Dulin et al, 1986;Choudhry and Webster, 1989;Kim and O'Keefe, 2000;Konstantinov et al, 2000) that for PCDDs, ®ssion of the ether bond in the dioxin ring is the most likely route for direct photolysis. However, reductive dechlorination, C±O cleavage, and hydroxylation all play a role in the photolytic transformation of PCDFs (Friesen et al, 1996).…”

“…The direct photolysis quantum yields Y and halflives (t 1=2 ) of six PCDDs reported by Choudhry and Webster (1989), the direct photolysis quantum yield of 2,3,7,8-T 4 CDD reported by Dulin et al (1986), and the direct photolysis quantum yields and half-lives of three PCDD and three PCDFs reported by Kim and O'Keefe (2000) were listed in Table 1 Choudhry and Webster (1989), and 3:6 Â 10 À5 (300 nm) by Kim and O'Keefe (2000), are comparable. Assuming the wavelength independence of Y, and for the consistency of the data set, the value reported by Choudhry and Webster (1989) was included in the QSPR study.…”

“…It was proposed from previous studies (Dulin et al, 1986;Kim and O'Keefe, 2000;Konstantinov et al, 2000) that for PCDDs, ®ssion of the ether bond in the dioxin ring is the most likely route for direct photolysis. So the following 14 descriptors were selected to describe the nature of the carbon±oxygen bonds to be broken in the photolysis.…”

“…Undoubtedly, if the number of PCDDs can be increased, the model will be blessed with a double portion of good fortune. Recently, Kim and O'Keefe (2000) reported on direct photolysis quantum yields and half-lives of three PCDDs and three PCDFs in water± acetonitrile (2:3 v/v) at 300 nm from the Rayonet RPR-3000 A lamps. This makes it possible for us to increase the number of PCDD/Fs in the training set and develop a new QSPR model, which is the purpose of this study.…”