Environ. Sci. Technol. 1994, 28, 1145-1 149
Formation of Polychlorinated Dibenzo-pdioxins and Polychlorinated Dibenzofurans during the Photolysis of Pentachlorophenol-Containing Water Stefan Vollmuth, Achim Zajc, and Reinhard Niessner'
Institute of Hydrochemistry, Technical University of Munich, Marchioninistrasse 17, D-81377 Munich, Federal Republic of Germany 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). Introduction Pentachlorophenol (PCP) is commonly used as a fungicidal and bactericidal agent, because it is toxic to plants, animals, and humans a t low concentrations (1,2). Furthermore, technical PCP contains polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF) as impurities, which are more harmful than PCP (1-3). Although since 1989 the production, sale, and application of PCP in Germany has been forbidden by law ( 4 ) , PCP can still be found in the total environment. High PCP concentrations (110-280 pg/L) have been detected in seepage water of landfills (5). In addition to chlorinated phenols, the seepage water is polluted with other organic compounds, like polycyclic aromatic hydrocarbons (PAH) and polychlorinated biphenyls (PCB). A new way to purify seepage water or wastewater is the irradiation of the water with ultraviolet (UV) light. The aim of the UV irradiation is the destruction of the organic compounds-in an optimum case completely to water, carbon dioxide, and mineral acids (6). In the studies, Crosby and Wong (7) determined the formation of octachlorodibenzo-p-dioxin(OCDD) during the photochemical treatment of PCP in water. They used alkaline solutions of 1 g/L of purified PCP and applied wavelengths greater than 300 nm. For a photochemical purification of PCP-containing water, it is necessary to examine the PCDD/PCDF 0013-938X/94/0928-1145$04.50/0
0 1994 American Chemical Society
generation under more realistic conditions. Therefore, we used PCP concentrations up to 1 mg/L and the irradiation wavelength of 254 nm as ultraviolet light with higher photon energy. This paper reports on investigations of the formation of PCDD/PCDF during the irradiation of several PCP-containing solutions. Experimental Section
Reagents. The solvents used in this work were toluene (nanograde),hexane (nanograde), dichloromethane (nanograde), and benzene (for pesticide residue analysis) from Promochem (Wesel,Germany) and acetone (distol solvent) from Fisons (Loughborough, U.K.). For the analysis of PCP and the three tetrachlorinated phenols (2,3,4,5-TCP; 2,3,5,6-TCP; and 2,3,4,6-TCP), standard solutions from Dr. Ehrenstorfer (Augsburg, Germany) were used. The PCDD and PCDF standard solutions were obtained from Cambridge Isotope Laboratories (Woburn, MA). For the cleanup, ICN Alumina B-Super I for dioxin analysis from ICN Biomedicals (Eschwege, Germany) was applied. Purification of PCP. PCP (1.0 g), whose purity has been described by the manufacturer as >99.3%, was quantitatively dissolved in 2 M NaOH. This solution was first extracted four times with 20 mL of toluene. Then the solution was acidified with concentrated HCl to pH 1 and subsequently extracted with 80 mL, with 40 mL, and for two times with 20 mL of toluene. The unified organic phases of the second extraction contained the PCP. The solvent removed, and the residue was recrystallized from acetone. Photolysis Conditions. Photolysis experiments were conducted with a Heraeus TNN 15/32 mercury lowpressure lamp (15 W, emission of 6 W for 254 nm). The lamp was placed in a cylindrical glass tube (Suprasil) and used as a dive lamp. The solutions (120 mL) were filled in a second cylindrical glass tube. During the irradiation, the solutions were stirred and the temperature of the solutions was kept constant by a thermostat at 19 "C. The time of irradiation was 5 h through all experiments. The PCP concentrations of the model solutions were 1 mg/L in the case of purified PCP and 0.92 mg/L in the case of technical PCP. Sample Extraction and Cleanup for PCDD/PCDF Analysis. After irradiation, 40 mL of 2 M NaOH was added to the solution to dissolve the chlorophenols quantitatively as phenolates. The irradiation apparatus was washed with 10 mL of toluene. Then, the irradiated solution was extracted three times with 10 mL of toluene, and the unified organic phases were dried over sodium sulfate. Next, the volume of the organic solution was reduced to 1 mL. For the cleanup, 25 g of Alumina E-Super I for dioxin analysis was filled in a column with a length of 55 cm and a diameter of 2.8 cm. A total of 3 g of Nap904 was stratified over A1203. After that, the column was rinsed with 70 mL of hexane. Then Environ. Scl. Technol., Vol. 28, No. 6, 1994 1145
Table 1. Blank and Detection Limit of PCDD Determination (n = 6), Confidence Interval with Probability of 0.95 blank concn PCDD
x f Ax (fg/L)
2,3,7,8-TCDD 14.1 f 28.1 1,2,3,7,8-PeCDD 384.9 f 453.3 1,2,3,4,7,8-H~CDD 209.9 f 369.3 1,2,3,6,7,8-H~CDD 32.1 f 53.9 1,2,3,7,8,9-H~CDD 241.8 f 274.5 1,2,3,4,6,7,8-HpCDD(HpCDDl) 619.0 f 465.1 OCDD 1239.8 f 607.4
Table 2. Blank and Detection Limit of PCDF Determination (n = 6), Confidence Interval with Probability of 0.95
detection limit xmin (fgiL) 101.8 1815.7 2299.4 297.3 1559.1 2181.1 4532.7
the 1-mL sample of the extract was put onto the top of the column. The first elution was performed with 80 mL of benzene, the second with 200 mL of a hexane/CHzCl2 mixture (98:2), and the third with 150 mL of a hexane/ CHzClz mixture (1:l). The last solution contained the PCDDs and PCDFs. Then, the solvent was reduced to a volume of 100 pL under clean nitrogen. Extraction for PCP Analysis. After extraction, the alkaline aqueous phase was acidified by concentrated HC1 to a pH of 1. Then the solution was extracted three times with 10 mL of hexane. The unified organic phases were dried over NazS04. The solvent was reduced to 100 pL under clean nitrogen. Gas Chromatography. Gas chromatographic PCDD/ PCDF and PCP analysis was performed on a H P 5890 Series 11. A DB 5 with a length of 60 m was used as capillary column. The film thickness of the column was 0.1 pm, and its inner diameter was 0.25 mm. The temperature of the injector was 270 "C. The temperature program started with 130 "C, which was held for 2 min. Then followed a heating rate from 40 "Cimin to 200 "C. This temperature was held for 10 min. After that followed a heating rate from 10 "C/min to 280 "C, which was held for 20 min. The next heating rate was 10 "Cimin to 300 "C. This temperature was held for 8 min. The sample was injected with a splitless injector. The total flow of the carrier gas helium was 20 mL/min. Mass Spectrometry. The detector was a high-resolution mass spectrometer (VG Autospec). The transfer line was heated up to 280 "C. The electron ionization (EI) took place with an electron energy of 31 eV and a trap current of 600 pA. The two electric fields of the mass spectrometer were operated at a voltage of 8000 V. The GC/MS run was performed in the selected ion-monitoring mode.
Results All results are given with a confidence interval Ax of P = 0.95. The methods were ensured by the determination
of blanks (Tables 1 and 2) and recovery rates (Tables 3 and 4) (8). The determination and quantitation of the PCDDs and PCDFs were only possible for the toxic 2,3,7,8chlorinated congeners. The detection limit for the analytical procedure rminis a function of the standard deviation of the blanks s b and were calculated by rmin= 3sb/B, where B represents the sensitivity of the GC/MS system calculated by B = AJCi (Ai, calibration peak area of congener i; Ci, calibration concentration of congener i) (8). The results of PCDDs/PCDFs are represented in toxicity equivalents (TEQ) according to NATOiCCMS (Table 5 ) 1148
Environ. Sci. Technoi., Voi. 28, No. 6 , 1994
blank concn detection limit x f Ax (fg/L) xmin (fg/L)
PCDF 2,3,7,8-TCDF 1,2,3,7&PeCDF 2,3,4,7,8-PeCDF 1,2,3,4,7,8-HxCDF 1,2,3,6,7,8-H~CDF 1,2,3,7,8,9-H~CDF 2,3,4,6,7,8-HxCDF 1,2,3,4,6,7,8-HpCDF(HpCDFl) 1,2,3,4,7,8,9-HpCDF(HpCDF2) OCDF
41.6 f 28.1 252.8 f 294.2 273.8 f 328.8 208.4 f 217.0 155.9 f 154.4 207.9 f 238.5 74.0 f 237.8 316.0 f 270.9 287.2 f 317.8 714.1 f 649.3
159.7 1234.2 1412.5 1130.8 792.6 1192.1 1357.7 1490.0 1749.7 3691.4
Table 3. Recovery Rate of PCDDs (n = 6), Confidence Interval with Probability of 0.95 PCDD
recovery rate ( % )
2,3,7,8-TCDD 1,2,3,7,8-PeCDD 1,2,3,4,7,8-HxCDD 1,2,3,6,7,8-H~CDD 1,2,3,7,8,9-H~CDD 1 2 3 4 6 7 8-HpCDD OdDD ' '
87.6 f 26.5 109.9 f 24.3 120.5 f 40.4 105.3 f 17.8 118.5 f 44.3 114.6 f 26.3 109.4 f 31.9
Table 4. Recovery Rate of PCDFs (n = 6), Confidence Interval with Probability of 0.95 PCDF
recovery rate ( % )
2,3,7,8-TCDF 1,2,3,7,8-PeCDF 2,3,4,7,8-PeCDF 1,2,3,4,7,8-H~CDF 1,2,3,6,7,8-HxCDF 1,2,3,7,8,9-H~CDF 2,3,4,6,7,8-H~CDF 1,2,3,4,6,7,8-HpCDF 1,2,3,4,7,8,9-HpCDF OCDF
97.6 f 26.5 106.0 f 21.2 97.4 f 18.4 115.1 f 39.2 97.1 f 18.6 101.6 f 21.3 105.1 f 30.0 114.0 f 21.8 112.3 f 27.2 110.6 f 31.0
Table 5. Calculation of Toxicity Equivalents (TEQ) According to NATO/CCMS (9) congener 2,3,7,8-TCDD 1,2,3,7,8-PeCDD 1,2,3,4,7,8-H~CDD 1,2,3,6,7,8-H~CDD 1,2,3,7,8,9-H~CDD 1,2,3,4,6,7,8-HpCDD OCDD 2,3,7,8-TCDF 1,2,3,7,8-PeCDF 2,3,4,7,8-PeCDF 1,2,3,4,7,8-HxCDF 1,2,3,6,7,8-H~CDF 1,2,3,7,8,9-H~CDF 2,3,4,6,7,8-HxCDF 1,2,3,4,6,7,8-HpCDF 1,2,3,4,7,8,9-HpCDF OCDF
factor 1.0 0.5 0.1
Ccongeners
factor
ZTCDD ZPeCDD ZHxCDD
0 0 0
ZHpCDD
0
ZTCDF ZPeCDF ZHxCDF
0 0 0
ZHpCDF
0
0.1 0.1
0.01 0.001 0.1 0.5 0.05 0.1 0.1 0.1 0.1 0.01 0.01
0.001
(9), while the blanks and detection limits are given in concentrations. Photolysis of Purified PCP in Model System. The concentration of the PCP solution was adjusted to 1mg/ L. The pH of the solution was buffered with a Na~B40,/ HC1buffer to pH 8. The PCDD/PCDF concentration was
I
‘uull
“
HpCDF1 HpCDF3 HpCDDI ‘OCDD HpCDFP OCDF HpCDD2
Before irradiation
I
After irradiation
I
OCDD HpCDFi HpCDF3 HpCDDi HpCDF2 OCDF HpCDD2
I
Before irradiation
After irradiation
I
Figure 1. Comparison of the PCDD/PCDF concentration before and after irradiation of a solution containing purified PCP.
Figure 2. Comparison of the PCDD/PCDF concentrations before and after irradlation of a solution containing technical PCP.
Table 6. TEQs of PCDDs before and after Irradiation of purified P C P According to NATO/CCMS
Table 8. TEQs of PCDDs before and after Irradiation of Technical P C P According to NATO/CCMS
2,3,7,8-substituted PCDDs
TEQs before irradiation
TEQs after irradiation (pg/L)
2,3,7,8-substituted PCDD
TEQs before irradiation (pg/L)
TEQs after irradiation (pg/L)
2,3,7,8-TCDD 1,2,3,7,8-PeCDD 1,2,3,4,7,8-HxCDD 1,2,3,6,7,8-HxCDD 1,2,3,7,8,9-H~CDD 1,2,3,4,6,7,8-HpCDD OCDD ZTEQ
nda nda nda 0.5 f 0.1 pg/L nda 0.9 f 0.3 pg/L 79.8 f 2.3 fg/L 1.5 f 0.3 pg/L
nda nda nda nda nda 90.0 f 72.0 116.7 f 89.6 206.7 f 114.9
2,3,7,8-TCDD 1,2,3,7,8-PeCDD 1,2,3,4,7,8-H~CDD 1,2,3,6,7,8-HxCDD 1,2,3,7,8,9-H~CDD 12 3 4 6 7 8-HpCDD ddDD ’ ’ ZTEQ
4.2 f 2.7 2.5 f 1.4 310.0 i 90.0 nda 9.3 f 18.6 999.0 f 244.0 606.0 139.0 1931.0 f 295.5
nda nda nda 7.0 f 4.0 nda 47.0 f 20.0 45.0 f 1.9 99.0 f 20.5
a
Not detectable; confidence interval with a probability of 0.95.
Table 7. TEQs of PCDFs before and after Irradiation of Purified PCP According to NATO/CCMS
*
Not detectable; confidence interval with a probability of 0.95. Table 9. TEQs of PCDFs before and after Irradiation of Technical P C P According to NATO/CCMS
2,3,7,8-substituted PCDF
TEQs before irradiation (fg/L)
TEQs after irradiation (pg/L)
2,3,7,8-substituted PCDF
TEQs before irradiation
TEQs after irradiation
2,3,7,8-TCDF 1,2,3,7,8-PeCDF 2,3,4,7,8-PeCDF 1,2,3,4,7,8-H~CDF 1,2,3,6,7,8-HxCDF 1,2,3,7,8,9-H~CDF 2,3,4,6,7,8-H~CI)F 1,2,3,4,6,7,8-HpCDF 1,2,3,4,7,8,9-HpCDF OCDF CTEQ
nda nda nda nda nda nda nda nda 13.0 f 9.0 11.0 f 3.9 24.0 f 9.8
nda nda nda nda nda nda nda 1.4 f 2.1 nda 6.4 f 5.2 7.8 5.6
2,3,7,8-TCDF 1,2,3,7,8-PeCDF 2,3,4,7,8-PeCDF 1,2,3,4,7,8-HxCDF 1,2,3,6,7,8-H~CDF 1,2,3,7,8,9-H~CDF 2,3,4,6,7,8-H~CDF 1,2,3,4,6,7,8-HpCDF 12 3 4 7 8 9-HpCDF OdDi ’ ’ ZTEQ
nda 6.5 3.8 pg/L 46.0 f 0.9 fg/L nda nda nda nda 62.0 17.0 pg/L nda 65.6 f 16.1 pg/L 134.5 f 23.7 pg/L
nda nda nda nda nda nd‘ nda 12.0 f 27.0 nda 1.7 f 0.9 13.7 f 27.0
*
*
Not detectable; confidence interval with a probability of 0.95.
Not detectable; confidence interval with a probability of 0.95.
determined before and after irradiation. The results are graphically presented in Figure 1. Tables 6 and 7 show the changes of the PCDD/PCDF TEQ values before and after the irradiation in detail. The concentration of PCP after irradiation was 37.7 f 116.7 ng/L. The reduction rate amounts to over 99.9%. It was impossible to detect any of the TCPs. Only heptaand octa-chlorinated PCDDs and PCDFs have been formed during the irradiation with UV light. In addition to 1,2,3,4,6,7,8-HpCDD, the formation of 1,2,3,4,5,7,9HpCDD (HpCDD2) was determined. The concentration of this non-2,3,7,8-congener was approximated to 5.6 f 3.8 ng/L. The ratio of 1,2,3,4,6,7,8-HpCDD) and 1,2,3,4,6,7,9-HpCDD after each irradiation amounts to 1:0.6. We could only determine the formation of 1,2,3,4,6,7,8-HpCDF and a second HpCDF (HpCDF3), which could not be distinguished between 1,2,3,4,6,8,9HpCDF and 1,2,3,4,6,7,9-HpCDF9The sum concentration of these non-2,3,7,8-congeners was approximated 0.7 f
0.5 ng/L. The ratio of these non-2,3,7,8-congeners and 1,2,3,4,6,7,8-HpCDF after each irradiation amounted to 5:l. Photolysis of Technical PCP-Na in Model System. The concentration of technical PCP-Na (Dowicide G, Fluka) in the pH 8 buffered solution was adjusted to 1 mg/L (0.92 mg/L of PCP). The PCDD/PCDF concentrations were determined before and after the irradiation. The PCDD and PCDF concentrations are shown in Figure 2. Tables 8 and 9 show the changes of the PCDD/PCDF TEQ values during the irradiation. The PCP concentration was reduced from 0.92 mg/L to 79.2 f 72.8 ng/L during irradiation. The reduction rate amounted to over 99.9%. TCPs were not detectable. Only 1,2,3,4,7,8-HxCDD and the 1,2,3,4,6,7,8-HpCDF were formed by irradiation. The other PCDD and PCDF congeners, which were impurities of the technical PCPNa, were reduced between 80.6 % and 100%. Environ. Sci. Technol., Voi. 28, No. 6. 1994
1147
3u-l
~~
1
HpCDFl HpCDF3 HpCDD1 OCDD HpCDF2 OCDF HpCDD2
rm Before irradiation Figure 3. Comparison of the PCDDIPCDF
After irradiation
1
concentrations before and
after irradiation of the seepage water. l _ _ _ l _ _ -
Table 16. TEQs of PCDDs before and after Irradiation of Seepage Water According t o NATO/CCMS 2,3,7,8-substituted PCDD
TEQs before irradiation (pg/L)
TEQs after irradiation (pg/L)
2,3,7,8-TCDD 1,2,3,7,8-PeCDD 1,2,3,4,7,8-H~CDD 1,2,3,6,7,8-H~CDD 1,2,3,7,8,9-H~CDD 1,2,3,4,6,7,8-HpCDD OCDD ZTEQ
1972.3 f 221.7 ndn nda 18.8 f 3.0 ndn 31.0 f 18.0 46.7 f 33.4 2068.8 f 224.9
576.7 f 239.1 nda nda 280.0 A 780.0 ndn 210.0 f 534.0 14.1 f 23.3 1080.8 f 975.3
a
Not detectable; confidence interval with a probability of 0.95.
Table 11. TEQs of PCDFs before and after Irradiation of Seepage Water According to NATO/CCMS 2,3,7&substituted PCDF 2,3,7,8-TCDF 1,2,3,7,8-PeCDF 2,3,4,7,8-PeCDF 1,2,3,4,7,8-H~CDF 1,2,3,6,7,8-H~CDF 1,2,3,7,8,9-H~CDF 2,3,4,6,7,8-H~CDF 1,2,3,4,6,7,8-HpCDF 1,2,3,4,7,8,9-HpCDF OCDF ZTEQ
TEQs before irradiation (pg/L)
TEQs after irradiation
nda nda nda ndn nda nda nda nda nda 2.5 f 1.3 2.5 f 1.3
ndn nda nda nda nda nda nda 33.0 f 95.0 fg/L nda 7.5 f 18.1pgiL 7.5 f 18.2 pg/L
a Not detectable; confidence interval with a probability of 0.95. -
Irradiation of Seepage Water from Landfill. The seepage water was analyzed to the important inorganic and organic impurities. The pH of the water was 7.0. The PCDD/PCDF concentrations before and after irradiation are shown in Figure 3. Tables 10 and 11show the changes of the PCDDiPCDF TEQ values during the irradiation. PCP was reduced during irradiation from 82.9 f 49.8 pg/L to 79.2 k 72.8 ng/L. PCP was reduced during irradiation from 82.9 f 49.8 pg/L to 79.2 f 72.8 ngiL. The reduction rate of PCP amounted to 99.2 % . 2,3,5,6-TCP was reduced from 390.0 f 190.0 pg/L to 509.0 f 247.0 ng/L. 2,3,4,5-TCP and 2,3,4,6-TCPcould not be distinguished by GCIMS. Their total concentration was reduced during irradiation from 88.3 f 42.0 pg/L to 323.3 f 119.9 ng/L. The reduction rates of the TCPs were 99.6% and 99.7%. OCDD was reduced about 69.3 % . After each irradiation, the forma1148
Envlron. Sci. fechnol., Vol. 28, No. 6, 1994
tion of 1,2,3,4,6,7,8-HpCDD and 1,2,3,6,7,8-HxCDDwas determinated. Because of the high confidence interval, a quantitative statement is impossible. The second HpCDD isomer-1,2,3,4,6,7,9-HpCDD (HpCDD2)-was also detected with an approximated concentration of 11.8 f 14.0 ng/L. The rate of 1,2,3,4,6,7,8-HpCDDand 1,2,3,4,6,7,9HpCDD after each irradiation was 1:0.6. Further, we could determine the formation of OCDF; 1,2,3,4,6,7,8-HpCDF; and a second HpCDF (HpCDF3), which could not be distinguished between 1,2,3,4,6,8,9-HpCDF and 1,2,3,4,6,7,9-HpCDF. The total concentration of these non-2,3,7,8-congeners was 12.2 f 16.5 pg/L. The rate of these two congeners and 1,2,3,4,6,7,8-HpCDF after each irradiation was 4.7:l. The most toxic congener 2,3,7,8TCDD was reduced about 70.8 5%. Discussion a n d Conclusions
The irradiation of several PCP-containing aqueous solutions indicated the formation of higher chlorinated PCDD and PCDF. The formation was obvious when the PCDD/PCDF concentrations before the irradiation were low. If the initial PCDD/PCDF concentrations were too high, only a reduction of the PCDD and PCDF was detectable. A complete reduction of PCDDiPCDF levels equal to the respective blank values seems not to be achievable under these conditions. A complete decrease of PCDD and PCDF can be reached by longer irradiation times or applications of high-pressure mercury lamps with higher energy than the low-pressure mercury lamp. A quantitative evaluation of the PCDD/PCDF formation is difficult because of the high confidence intervals of some irradiation results. This is not a consequence of the low precision of the analytical procedure but of the repeated irradiations. Each irradiation depends on many unknown factors, which lead to divergent results. The concentrations of formed PCDD and PCDF are in all cases definitely above the detection limit. Thus, qualitative conclusions are permissible. During the irradiation of pure PCP, the TEQ can increase about by a factor of 150 by the formation of HxCDD, HpCDD, OCDD, HxCDF, HpCDF, and OCDD. It was striking that the ratios between the generated heptachlorinated PCDDs and the generated heptachlorinated PCDFs were similar. These results lead to the concludion that the photochemical formation under the applied conditions is uniform. The mainly produced heptachlorinated congener is the 1,2,3,4,6,7,8-HpCDD. Hence it follows that the heptachlorinated congeners are formed by the photoinduced dechlorination of OCDD, because a condensation of PCP and TCP produces mainly 1,2,3,4,6,7,9-HpCDD. We assume the same reaction for the formation of the heptachlorinated dibenzofurans, although OCDD preferently loses the chlorine atom in the peri-position next to the ether bridge and the OCDF also preferently loses the chlorine atom in the peri-position next to the C-C bridge (Figure 4). In contrast to these results, Buser et al. (10)determined the loss of the chlorine atom preferentially in the lateral position (2, 3, 7 , 8 ) during the irradiation of OCDD in an organic solvent. High PCP, TCP, PCDD, and PCDF concentrations can be reduced by UV irradiation. During irradiation of solutions with low PCDD/PCDF and high PCP concentrations, a significant increase of PCDD/PCDF
OH
cl*cl CI
CI CI
l
p
C
p
\ CI
cl+o*cl
CI
CI
0
CI
CI
CI
CI
CI
CI
CI
CI
CI
OCDD
hv
1
-
CI
OCDF
CI
hv
'
CI
CI
CI
1,2,3,4,6,7,8-HpCDD
1
-
CI
'
CI
can be explained by the extreme optical properties of the seepage water (Figure 5). High concentrations of heavy metal cations and other organic compounds are responsible for the high absorbance of the seepage water. The heavy metal cations especially have the effect of a filter for UV light. Thus, only very diluted solutions with a higher transmission or treating in a thin-film arrangement will probably yield higher destruction rates. Respective research is currently under study. PCP and TCP have been reduced with rates greater than 99.0%. With regard to a photochemical purification of PCP-containing water, it will be necessary to avoid any formation or to force the destruction of PCDDs and PCDFs. A proposed method is the combination of UV irradiation and oxidizing reagents like ozone or hydrogen peroxide (10). Another possibility may be the use of a photocatalyst like titanium dioxide (11, 12). A further conclusion is that an uncritical use of UV destruction techniques should be avoided. The exact control and monitoring of the course of the mineralization process is strictly necessary. L i t e r a t u r e Cited
CI
1.2.3,4,6,7,8-HpCDF
Flgure 4. Photochemical formatlon of PCDDs and PCDFs during the UV irradiation of PCP-containing water samples.
(1) World Health Organization. Pentachlorophenol. Environ. Health Criter. 1987, No. 71. (2) Crosby, D. G.; Beyon, K. I.; Greve, P. A.; Korte, F.; Still, G. G.; Vonk, J. W. Pure Appl. Chem. 1981,53, 1051-1080. (3) World Health Organization. Polychlorinated Dibenzo-pdioxins and Dibenzofurans. Environ. Health Criter. 1989,
"
4,5
" ,
200
300
400
500
600
760
800
Wavelength [nm]
Flgure 5. UV absorptions spectrum of the seepage water.
concentration has been observed. For this season, the method of UV irradiation to purify PCP-containing water samples could be problematic, because the destruction of a toxic compound is accompanied by the formation of a more toxic and more photochemically stable compound. The moderate reduction rates during the irradiation of the seepage water in contrast to the irradiations of the model system (solution of purified and technical PCP)
No. 88. (4) Pentachlorverbotsverordnung (PCP-V). Bundesgesetz blatt 1989, No. 59, 2235. (5) Hagen, K.; Kretzschmar, W.; Scharff, K. G W F , Gas- Wasserfach: WasserlAbwasser 1993, 134, 208-212. (6) Yue, P.; Lengrini, 0. Water Pollut. Res. J. Can. 1992, 27, 123-137. (7) Crosby, D. G.; Wong, A. S. Chemosphere 1976,5,327-332. (8) Doerffel, K. I. In Statistik in der Analytischen Chemie, 3rd ed.; Verlag Chemie: Weinheim, 1984; pp 85-101. (9) Fiedler, H.; Hutzinger, 0.;Timms, C. W. Toxicol. Environ. Chem. 1990,29, 157-234. (10) Buser, H.-R. J. Chromatogr. 1976, 129, 303-307. (11) Palauschek, N.; Scholz, B. Chemosphere 1987, 16, 18571863. (12) Pelizzetti, E.; Borgarello, M.; Minero, C.; Pramauro, E.; Borgarello, E.; Serpone, N. Chemosphere 1988, 17, 499510. (13) Mills, G.; Hoffmann, M. Environ. Sci. Technol. 1993, 27, 1681-1689.
Received f o r review October 18, 1993. Revised manuscript received January 24, 1994. Accepted February 3, 1994.' Abstract published in Advance ACS Abstracts, March 15,1994.
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