Document EvKgzvxbMozeqje9b0arNrz2L

Photochemical Degradation of Di- and Octachlorodibenzofuran by 0. Hutzinger,* $. Safe,* B.R. Weitzell/ and V. Zitko* Introduction In the fast few years, it has been shown that polychlorinated biphenyls undergo de composition on irradiation with artificial ultraviolet light sources and sunlight {1-7). Reductive dehaiogenation of one or more chlorine atoms was a major reaction, par ticularly in hydrocarbon solvents. In fluoro carbon solvents or thin films, small quanti ties of chlorobiphenyls with increased chlo rine content could also be detected. Irradia tion in hydroxylic solvents gave the dechlorinated species as well as photoproducts containing oxygen. In addition, chlorinated terphenyls and quaterphenyls were also de tected in some instances, and on prolonged irradintion polymeric products were formed. It lias been speculated for some time that chlorodibenzofurans may be formed from chlorobiphenyls under photochemical condi tions which lead to oxygenated products. Al though no chlorodibenzofurans could be de tected in a number of chlorobiphenyl sam ples which had been exposed to sunlight for over 2 months (4), preliminary results in dicated the formation of chlorodibenzofur- Atlnnlic Regional Laboratory, National Research Council of Canada, Halifax, Nova Scotin, Canada. fPeparlmont of Chemistry, Acadia University, WoJfville, Nova Scotia, Canada. J Environment Cunnda, Fisheries nnd Marine Serv ice, SI. Andrews, New Brunswick, Canada. ans from 2,2',4,4',6,6'-hoxHch]orobiphenyl in model experiments (irradintion in methanol) <*). The toxicity of pure chlorodibenzofurans has not been thoroughly investigated (0) but appears to be higher by several orders of magnitude than that of the chlorobi phenyls, which gives this reaction particular significance. In this regard, the photochemical behav ior of chlorodibenzofurans themselves be comes of interest from the point of view of products formed (decomposition to less tox ic products) and stability. As an approxima tion [eq. (1)], it appears that if chloro dibenzofurans are formed from chlorobi phenyls in the environment by photochem ical reaction, accumulation will be a problem if ft, > ft,. Chlorobiphenyl --chlorodibenzofuran - ^ ^ decomposition products (1) Since a good selection of chlorodibcnzo- furans is not available, only preliminary investigations with two representatives, one of low (2,8-dichlorodibenzofuran) and one of high chlorine content (octachlorodiben zofuran) are reported. Equipment and Methods Chemicals 2,8-Dich!orodil>enzofuran (10) and octa chlorodibenzofuran (11) were prepared by September 1973 2<7 HONS 081577 literature methods. Samples for the initial experiments were provided by Dr. A. E. Pohland, (FDA, Washington, D.C.) Irradiations For the irradiations in solution (450 ml hexane or methanol), a Rayonet (the South ern New England Ultraviolet Co.) photo chemical reactor equipped with 16 RPR8100 lamps (310 nm) was used. Aliquots (25 ml) were taken at times specified in Figure 1. For mass spectrometric analysis of the photolysis mixture, 2,8-dichlorodibenzofuran and octachlorodibenzofuran were irradiated in methanol for 20 min. Thin films (50 mg) of the chlorodibenzofurans coated on the inside of quartz tubes (length: 25 cm; diameter, 4 cm) were ex posed to sunlight for 10 weeks in the pres ence of water (2 ml) during July-September 1972. Total duration of bright sunshine was ca. 580 hr (Meteorological Services, Canadian Forces Base, Shearwater, N. S,, private communication). Instruments Quantitative data were obtained with a Packard model A7901 instrument equipped with 6 ft x 4 mm columns packed with either 4 SE-30 (for the 2,8-dichlorodibenzofuran) or 3% OV-210 (for the octach lorodibenzofuran) on Chromosorb W. A DuPont/CEC 21-110B double focussing mass spectrometer was used for obtaining spectra by direct introduction. The probe was heated carefully, and spectra were re corded as the temperature was raised from 20C to ca. 180#C. Analysis of Samples Quantitative analyses (photochemical stability of chlorodibenzofurans) were car ried out by gas chromatography (GC) with electron capture detection on the aliquots taken from the photochemical reactor. For the characterization of products formed, the solvent was removed from the samples and the residue chromatographed on Merck silica thin-layer plates (F-254; 0.25 mm thickness). The solvent used was hexane. For the mass spectroscopic analy sis, small fractions of the total sample were transferred to a mass spectrometer sample tube. Samples from the quartz tubes were dissolved in benzene-acetone and treated as described above. Results and Discussion The correct numbering of the dibenzofuran ring system (Chemical Abstracts and Ring Index) is shown in Figure 2. 9I Figure 1. Photochemical degradation of chlorodibenxofurans in aolution. Irradiation wavelength 310 nm. 6 54 Figure 2. Numbering of the dibenzofursn nucleus. 2G8 Environmental Health Perspectives MONS 081578 Some older systems are still in use occasion ally. Calculated molecular weights (Cl - 85) for dibenzofuran and its chlorine substitu tion products are given in Table 1. Tib)* 1. Molecular weight! for chlorodibensofurani (monoiioiopic formula; Cl = IS) Formula CmH.O C.rH.CIO C..H.CI.0 CmH.CUO CitH.Cl.O C.,H.CI.O C..HrCUO CH Cl0 C..CI.0 Molecular weight 168 202 236 270 304 338 372 406 440 Irradiation of 2,8-Di-and Octachlorodibentofuran in Solution The relative rate of decomposition of 2, 8-di- and octachlorodibenzofuran is shown In Figure 1. From these results and from the mass spectra of samples which were ir radiated for 20 min it is evident that de composition is faster in methanol than in hexane. In contrast to the chlorinated dibenzo-p-dJoxins, where the degradation of the octachloro derivative on irradiation in methanol aolution la much slower than that of the 2,7-dibenzo-p-dioxin (12), the di- and octachlorodibenzofurans show similar rates of decomposition. For the analysis of products formed, sam ples which were irradiated for 20 min in methanol (short exposure) and for ca. 20 hr in hexane (long exposure) were chosen. Thin-layer chromatography, of the sam ples exposed for 20 min showed only two spots, a relatively weak one on the origin and a large spot with an R< similar to those starting materials (Rf - ca. 0.55 for 2,8-dichlorodibenzofuran; Rt - ca. 0.75 for octachlorodibenzofuran). Since organochlorine compounds which give very strong molecular ions can be analyzed by mass spectrometry in mixtures (/g-15), samples of the irradiated prod ucts were carefully heated in the mass spectrometer probe and spectra recorded at different temperatures. Typical spectra are shown in Figures 3 and 4. No other products but those formed by dechlorination of the corresponding chlorodibenzofuran were found to be present. No useful mass spectra could be obtained for the yellow gum which resulted from the 20-hr irradiation experiments. A large num ber of peaks was observed and no recogniz able chlorine isotope pattern was apparent. Cl, photolysis of c'rv-f^rc' *IO / Dlbenrofuranv^ Ol-------.------- .------- .-------.------- r-------1 100 ISO 1, , , 200 m/e (methanol) *10 T ------- ,------- ------- .------- .------- .------- , 250 300 Ftc.VKE 3. Mm spectrum (70 eV) of 2,8-dlchlorodibcnzofuriin photolysis mixture (310 nm; 20 min; solvent methanol). Probe temperature: 40* C. September 1D73 269 HONS 081579 photolysis _of m --1------- 1------- "P" 320 l-------- 1 360 , imui | -------- ,--JJ+i 400 m/e r------- ,--------l-^S 440 ,-------- ,-------- , 400 Figure 4. Muss spectrum (70 eV) of octachlorodibensofuran photolysis mixture (310 nm; 20 min; solvent; methanol). Probe temperature: 30* C. Exposure of 2,8-Di- and Octachlorodibenzo* furan as Thin Film to Sunlight The analysis by mass spectrometry was carried out as described above. Reductive dechlorination of octachlorodibenzofuran was observed to a much lesser degree than in solution. 2,8-Dichlorodibenzofuran gave, in addition to a monochloro derivative, a trichlorodibenzofuran (M`-270). A summary of the results of the photoly sis experiments in solution and thin films is shown in Figures 5 and 6. Summary and Conclusions Photolysis of 2,8-di- and octachlorodiben zofuran in methanol and hexane solutions results in rapid dechlorination of the sub strates with the eventual accumulation of Figure 5. Summary of results from 2,8-dichiorodiberuofurnn irradiation experiments. 270 Figure 6. Summary of results from octachlorodi benzofuran irradiation experiments. unidentified resinous polymeric products. Dechlorination is also observed to r certain extent when thin films of these compounds were exposed to sunlight. These preliminary data do not allow dir ect comparison of dibenzofuran degradation rates with rates of photochemical formation from corresponding chlorobiphenyls (S). In view of the photochemical lability of chlorodibenzofurans, however, it seems unlikely that accumulation of these compounds formed from chlorobiphenyls by photochem ical reaction in the environment will occur. REFERENCES 1. Safe. S., and Hutzingcr, 0. Polychlorinated bi phenyls: photolysis of 2,4,0,2','l'6'-hexnchlorobiphenyl. Nature 232: B41 (15)71). Environmental Health Perspectives HUNS 081580 2. Hustcrt, X., and Korte. F. Synthes* polychlorlerlcr Biphenyls und ihrt Reaktion bei UVBcstrohlung. Chemosphtre I: 7 (1972). 3. Hutsinger, On Safa, S., and Zitko, V. Photo* rhrmirnl degradation of chlorobiphenyls. En viron. Health Perspect. 1: 15 (1972). 4. Hutsinger, 0., at al. Photochemical degradation of iaomarically pure di-, tetra-, hexa-, octa-, and decachloroblphtnyla. Paper presented at 104th Meeting, American Chemical Society, Division of Water, Air and Waste Chemistry 1972; Ab stracts: 74 (1972). 6. Herring, J. L., Hannan, E. J., and Bills, D. D. UV irradiation of Aroclor 1254. Bull. Environ. Contam. Toxicol. Sr 158 (1972). Q. Ruto, I* 0., Zabik, M. J., and Schucts, R. D. Polychlorinated bipheryla: photolysis of 3,4,S',4'tetrachlorobiphonyl and 4,4'-dichlorobiphenyl in solution. Bull. Environ. Contam. Toxicol. S: 217 (1972). 7. NUhiwakl, T,, ct al. Dechlorination of poly chlorinated biphenyls by UV irradiation (in Jap anese). Nippon Kagnku Kaishi: 2226 (1972); Chem. Abstr. 78: 29839 (1973). g. Andersson, K., et al. Photochemical degradation of polyhalogenated biphenyls. Paper presented at PCB Conference II, Stockholm, 1972. 9. Vos, J. C., et al. Identification and toxicological evaluation of chlorinated dibenzofuran and chlorinated naphthalene in two commercial poly chlorinated biphenyls. Food Cosmet. Toxicol. 8: 525 (1970). 10. Gilman, H.t et al. Dibenzofuran. III. Nuclear substitutions. J. Amer. Chem. Soc. 56: 2473 (1934). 11. Hutsinger, O., Safe. S., and Zitko, V. Analysis of chlorinated aromatic hydrocarbons by exhaus tive chlorination. Int. J. Environ. Anal. Chem. 2: 96 (1972). 12. Crosby, D. G., et al. Photodecomposition of chlorinated dibenzo-p-dioxins. Science 173: 748 (1971). 13 Hutzinger, 0., Jamieson, W, D., and Zitko, V. Identification of polychlorinated biphenyla and DDT in mixtures by mass spectrometry. Nature 226: 664 (1970). 14. Hutsinger, 0., and Jamieson, W. D. Identifica tion of organochlorine pesticides in crude ex tract* by mass spectrometry. Bull. Environ. Contain. Toxicol. 55: 587 (1971). 15. Hutsinger, 0., and Jamieson, W. D. Application of high resolution mass spectrometry to residue analysis: identification of organochlorine and organometallic pesticides and pollutants in crude extracts. Pesticide Chemistry, (Proc. 2nd In ternational IUPAC Congress), A. S. Tahori, Ed., Vol. 4, 1971, p. 7. September 1973 271 mons oai5ai