Photolytic Method for Destruction of Dioxins in Liquid Laboratory Waste and Identification of the Photoproducts from 2,3,7,8-TCDD

Abstract

Analytical and other research laboratories that generate small volumes of dioxin-containing wastes have no convenient method for their disposal. We have used ultraviolet photolysis with a low-pressure mercury lamp to destroy dioxin-like compounds, both as individual congeners and in actual waste analytical samples, down to nondetect levels. Photolysis promises to be an efficient, safe, and inexpensive method for on-site treatment of liquid laboratory wastes that are contaminated by dioxin-like compounds, allowing the treated materials to be discarded as regular organic solvent waste. Experiments with 1,6-[3H]-2,3,7,8-TCDD revealed that the principal photolytic pathway involves cleavage of C−O bonds rather than C−Cl bonds, giving chlorinated hydroxydiphenyl ethers as the initial products and accounting for the low material balances of reductive dechlorination products previously found upon photolysis of PCDDs. The photolysis products from 2,3,7,8-TCDD do not bind to either the Ah receptor or the estrogen receptor in vitro, making it unlikely that the products from UV treatment of PCDD/PCDF in laboratory waste will show either Ah or estrogen receptor-mediated toxicological effects.

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

“…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).…”

“…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.…”

Photodegradation of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans: Direct photolysis and photocatalysis processes

“…The photodegradation rates for PCDD/Fs generally decrease as the degree of chlorination increased in single-compound condition (Tables 4 and 5); conversely, this study obtained the opposite finding for mixedcompound conditions ( Table 2). Most works in this area focused on photolysis of PCDD/Fs in water solution, organic solvents, on plant surfaces, and in other environments [7][8][9][27][28][29]. Kluyev et al [6] found that zero valence iron can be utilized for the stepwise dechlorination of OCDD in water at 250 • C. Ukisu and Miyadera [30] dechlorinated 2, 7-DCDD and 1, 2, 6, 7-TCDD in a solution of NaOH in propanol in the presence of carbonsupported noble metal catalyst (Pd/C and Rh-Pt/C).…”

“…Care must be taken to control the generation of byproducts that may be more toxic than the parent pollutants when mineralization is incomplete. The 2, 3, 7, 8-substituted PCDD/Fs products were not detected in photocatalysis experiments, perhaps due to the following reasons: (i) the photocatalytic degradation involved cleavage of the aromatic ring [11], and/or (ii) removal of lateral chloros (2,3,7,8) was favored over removal of longitudinal chloros (1,4,6,9) from PCDDs. Although photodegradation of OCDD in the solution phase involves preferential chloro loss at lateral positions over loss at longitudinal positions [13,31], as with HxCDD [6], congeners with longitudinal chloros degrade more rapidly than those with laterally substituted chloros in the surface-phase reaction [32].…”

“…One method is to extract PCDD/Fs from spent carbon or ash and then apply an effective method for degrading the dioxins. Several methods have been considered in the development of an efficient and economically feasible approach for destroying PCDD/Fs, including catalytic destruction [6], photolysis [7][8][9][10], photocatalysis [10][11][12], radiolysis [13], ozonolysis [14], and biodegradation [15,16]. Although biological processes are frequently favored for contaminated site remediation, photodegradation is an effective and rapid treatment.…”