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ANALYTICAL CHEMISTRY, VOL. 50, NO. 6, MAY 1978
Gas Chromatographic Determination of 2,3,7,8-Tetrachlorodibenzodioxin in the Experimental Decontamination of Seveso Soil by Ultraviolet Radiation Giuliano Bertoni, Domenico Brocco, Vincenzo Di Palo, Arnaldo Liberti, Massimiliano Possanzini, and Fabrizio Bruner Laboratorio sull'Inquinamento Atmosferico de/ C.N.R., Via Montorio Romano, 36-00 13 1 Rome, Italy
EXPERIMENTAL
I t is shown that gas chromatography using packed columns and EC detector is a suitable analytical tool for the analysis of environmental samples containing TCDD from Seveso, Italy. With this technique the successful experiments of photodegradation of TCDD by sun light or artificial UV radiation have been monitored. With the purification procedure described, the minimum detectable concentration in soil samples is about 7.0 nglkg. I t is also shown that more than 90% of dioxln content is destroyed after 7 days' exposure to sunlight when soil is sprayed with a solution of ethyl oleate in xylene.
Checking the Analytical Procedure. In order to verify the analytical method used to check the effectiveness of UV decontamination, samples of agricultural suburban soil similar to that of the Seveso zone was chosen and underwent the following procedure: 30-40 g of soil are first dried in a rotating drum at about 60 "C to eliminate excessive moisture, after elimination of big stones, grass, roots, and other gross impurities. The soil is then sieved through a 4-mm2 net sieve. A known amount of TCDD in benzene is added to the soil with a procedure similar to that used for coating the solid support of columns in gas chromatography. A layer of soil, about 1 cm deep is made in a flat glass capsule and a highly diluted solution of TCDD in benzene is added to obtain a TCDD concentration in the soil of about 10 lg/kg. After solvent evaporation at room temperature, the photosensitizing agent, ethyl oleate-xylene 1:2, is added as a spray to the soil. Preliminary experiments showed that the best amount of the mixture is 150 mL/m2 to decontaminate a soil layer of 1 cm, that corresponds to about 0.5 mL/g. Higher amounts have a negative effect on the analysis and do not improve the TCDD degradation. The following procedure is used for the analysis. The soil sample is placed in a chromatographic column (20 cm long, 2.5-cm id.) equipped with a frit glass septum and the organics are eluted with 100 mL benzene. The benzene extract is concentrated to 1 mL by evaporation under a nitrogen stream at about 50 "C in a water bath, and transferred in a chromatographic column (10 cm long, 0.8-cm i.d.) containing 2 g of activated alumina (8 h at 130 "C, activity 1 according to Brockman). The elution is made with 10 mL of a solution of n-hexane and CC1,l:l v/v followed by 10 mL of n-hexane-methylene chloride 1:l v/v. The former eluate contains PCBs and possibly PCNs. The latter contains TCDD and pesticides and it is concentrated to 2 mL. Then up to 50 drops of concentrated H,S04 are added while shaking. Two phases are formed. The sulfuric acid phase (dark) is extracted three times with the n-hexane-methylene chloride solution that is added to the organic phase. This is filtered on Al,O, and washed out with the same solvent mixture up to a total volume of the organic phase of 10 mL. This solution is now concentrated to 1 mL by gentle evaporation, transferred in a tailed tube, and dried at room temperature. Finally 100 pL of benzene are added to make the solution ready for GC analysis. TCDD recovery is always higher than 90% (see Table I) in all the measurements carried out. The procedure followed for the sample treatment of the Seveso soil is analogous, eliminating the drying step. In some cases, when the soil is very wet, water causes some difficulties, so that the Seveso soil is allowed to loose its excessive moisture content in the sunlight before spraying it with the sensitizing mixture. TCDD content is checked before and after several days of exposure to sunlight and no decrease in its content is observed in the absence of the sensitizing mixture. TCDD recovery is somewhat lower when the soil is wet, especially when its content is relatively low. The results of the recovery experiments with Seveso soil are reported in Table I and will be discussed later. Gas Chromatographic Equipment. The major problem to be solved is the ECD calibration and response constancy. In order to produce reliable calibration curves, the column with the proper
T h e rupture of a safety valve in a plant for the production of 2,4,5-trichlorophenol provoked a cloud of this compound containing reagents and undesired products t h a t polluted a vast area in t h e town of Seveso, (Milan). 2,3,7,8-Tetrachlorodibenzodioxin (TCDD) was the most toxic and polluted both soil and houses. Since the first days after the Seveso disaster, our laboratory was deeply involved in the search for a feasible method for the decontamination of t h e Seveso soil and houses. In particular, our attention was devoted to the destruction of the TCDD molecule by UV radiation according to the suggestions made by Crosby and Wood ( I ) . Details of this method have been reported elsewhere (2),and also the results of the first laboratory experiments have been recently published (3). For the determination of TCDD in soil, there is no doubt t h a t t h e most suitable and reliable method reported in the literature is offered by soil extraction and purification followed by high resolution GC separation ( 4 ) and identification by mass spectrometry or better, mass fragmentography (5-7). T h e use of an on-line computer is desirable in the latter case. High resolution gas chromatography is an alternative way that may solve the problem without making use of t h e mass spectrometer. Because of the relatively limited number of sophisticated apparatus available, when an extremely high number of analyses is required in order to obtain a detailed map of the distribution in the polluted area and to monitor its persistence and evolution, and to check biological samples, a strong need for a simpler and a t t h e same time reliable method to carry out routine analysis of the TCDD content of soil samples is felt. This is particularly true in the case of our laboratory, involved in successive experiments on decontamination by UV rays, because of the necessity of obtaining fast analytical responses. In particular, the experiments being confined at the moment to the most polluted area, and because of the particular sample extraction and concentration procedure used. the amount of TCDD is always relatively high with respect to other chlorinated compounds present. For all these reasons, the method here described has been devised for our experimental studies on TCDD decontamination. 0003-2700/78/0350-0732$01 O O / O
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1978 4merican Chemical Society
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Table I. TCDD Recovery in the Extraction Process from Seveso Soil in the Presence of an Ethyl Oleate-Xylene Mixture Sample Initial amount After alumina After H,SO, After glass No. of TCDD pig column treatment ware changes Total Average 1 2 3 4 5
0.5
102
98
100
100
0.5 0.2
98 95 96 96
100
96
95 96 98
94
94 85 89 86
0.2 0.2
type and amount of stationary phase has been selected. Chromatograph and detector temperatures have been also carefully chosen. A Carlo Erba model 2101 gas chromatograph equipped with a 63Ni ECD with the detector in the pulse mode (40 V, 100-ps period, 10-ps width) has been used. Calibration is tnade after conditioning the entire equipment and by testing the detector response to a given amount of TCDD injected time to time. Linear detector response has been found in the range between 0.020 to 200 ng. The lower detection limit in the chromatographic conditions of routine analysis is 0.20 ng, with a signal to noise ratio 5 1 . Lower signal to noise ratios can still be of use when pure TCDD samples have to be qualitatively analyzed but this is not the case when real soil samples, with many impurities in spite of the purification procedure. are to be analyzed. The best detector temperature is 240 “C. Attempts to obtain efficient and selective separations failed with a 1.5 m X 2 mm i.d. glass column coated with 3% XE60 on Chrornosorb G AW 80-100 mesh and with a glass column 1.6 m packed with Chromosorb GAW 100-120 mesh + 0.1% H2P04+ 0.6% PPE 20. The efficiency of such a column was rather good, but selectivity was relatively poor with respect to the separation of pesticides from TCDD. The best column was found to be a 3-m, 2-mm i.d. glass tube containing Supelcoport 100-120 mesh + 1.570 SP2250 + 1.95% SP2401. This is the Supelco analogous to the best column found in the literature ( 8 )for pesticide analysis (1.5’70 OV-17!1.957~ QF-I). This column yielded about 6000 theoretical plates on the TCDD peak at 6.2 cm/s average linear gas velocity. Such performance was obtained just after column preparation and conditioning. Column efficiency decreased about 15-20%’ with use, reaching a constant value of about 5000 plates. With such conditions, at 205 “C an artificial mixture of pesticides and TCDD was well separated. The most difficult separation is that of TCDD and p,p’-DDT, and this interference gives bad quantitative results if the ratio of DDT to TCDD peak areas is higher than 1O:l. The most worrisome interference is given by PCBs that are present in the Seveso soil in about the same amounts as pesticides, in the retention time region of TCDD. Higher amounts of PCBs are present at longer retention times. For all these reasons, a careful purification of the soil sample is needed. Other possibile interferences are given by chlorodibenzvfurans, that could be present as side products of the preparation of trichlorophenols (4). A GC-MS apparatus not equipped with the facilities for mass fragmentography has been employed to check the retention time of TCDD and its presence in real soil samples. An AEI MS12 mass spectrometer modified for better GC-MS applications (9) was used. The presence of polychlorobenzofurans was not detected in the samples of soil examined.
RESULTS AND DISCUSSION T h e extraction procedure is a modification of the well established procedure found in the literature (10, I I ) , the only changes being related t o the different nature of the samples. Major differences are due to the presence of massive amounts of an ethyl oleate and xylene 1:2 mixture t h a t is spread on the soil prior to irradiation as a hydrogen donor. The reasons for this choice have been described elsewhere ( 3 ) . In order to destroy the ethyl oleate, concentrated sulfuric acid is added to the solution drop by drop with shaking. The accepted procedure is slightly different and the sulfuric acid treatment is made by flowing the solution through a H2S04 soaked celite column. With our method the amount of HISOl is higher and ensures a complete destruction of ethyl oleate,
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Figure 1. GC separation of TCDD from chlorinated pesticides in an artificial mixture. Column: 2 m X 2 mm i.d. glass. Supelcoport 110-120 mesh -t 1 . 5 % Sp 2250 -t 1.95% SP 2401. T = 205 OC isothermal. P = 3.0 kg/cm2. Peak identification: (1) a-BHC, (2) Lindane, (3) P-BHC, (4) Heptachlor, (5) Aldrin, (6) Heptachlor epoxide, (7) p,p’-DDE, (8) Dieldrin, (9) TDE, (10) Endrin, (11) o,p’-DDT, (12) p,p’-DDD, (13) TCDD, (14) p,p’-DDT
avoiding at the same time the danger of irreversible adsoption on celite. In Table I, the recovery of TCDD a t different stages of the purifications and in the overall process is reported for the soil in the presence of ethyl oleate. This is in agreement with that found in the literature cited and by other Italian laboratories in routine determinations. In Figure 1 an artificial mixture of chlorinated pesticides has been analyzed with the 3-m column containing Supelcoport 100-120 mesh coated with 1.5% SP2250 + 1.95% SP2401. TCDD, 0.8 mg, have been added to the mixture which resulted in full separation from pp’-DDD while a 75% separation is achieved with respect to p,p’-DDT. The retention time of TCDD was further checked by mass spectrometry with a low scanning in the region of the molecular ions. Masses 320,322, 324, and 326 have been monitored on the reference solution and in some of t h e soil samples particularly rich in TCDD. T h e ratios of the four masses’ abundance resulted as being consistent with t h e mass spectrum of TCDD. Samples of soil uncontaminated by TCDD were also processed and analyzed with our procedure and no peaks were found between the p,p’-DDD and p,p’-DDT peaks. Interferences from PCB are fully eliminated by the purification procedure. Arochlor 1254 and Arochlor 1260 are those that show most peaks around the retention time of TCDD. In Figure 2, chromatograms of the two PCB mixtures with and without TCDD added are shown. It can be seen that there is some resolution of the latter compound from all the other peaks in both cases. In Figure 3A Arochlor 1254 and 1260 are eluted together with TCDD. Because of t h e strong differences in the relative amounts of TCDD and Arochlors, the peak obtained from the former is almost hidden by other peaks. However, it is interesting to note that a difference in retention time of TCDD from any other peak is still observed. This is only possible because of the higher efficiency of the column used here with respect to those of the literature ( 8 ) .
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ANALYTICAL CHEMISTRY, VOL. 50, NO. 6, MAY 1978
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Flgure 2. Chromatograms of Arochlors showing the separation of TCDD. (A) Arochlor 1254, (B) Arochlor 1254 -t TCDD, (C) Arochlor 1260, (D) Arochlor 1260 TCDD. Chromatographic conditions and column as in Figure 1. Relative amount of TCDD to PCB, about 10% in all chomatograms
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Figure 3. Purification of TCDD from PCBs. (A) Arochlor 1254 (5.00 pg) Arochlor 1260 (5.00 pg) -t TCDD (0.32 pg) in 1 rnL n-hexane. Sample injected, 2 pL. (B) Same mixture after purification, concentrated to 0.1 mL. Sample injected: 1 pL
+
In Figure 3B the same mixture is analyzed after following the purification procedure and it is shown that the TCDD peak remains practically alone, together with some peaks eluted much after or before. From all these experiments, it can be inferred that the PCBs interference is eliminated with the purification method used. A typical chromatogram obtained from the Seveso soil after purification is reported in Figure 4, where some pesticides have been identified. A large peak of p,p'-DDT is observed. This substance is always present in soil, but its amount is extremely different in various samples. The particular sample shown is one of those where p,p'-DDT is present in the largest amount. I n Figure 5 , the analysis of the same sample of Seveso soil reported in Figure 4 is shown after 5 days of exposure to solar radiation in the month of July 1977, the soil being previously spread with a mixture of ethyl oleate and xylene. A degradation of TCDD about 80% is observed. Also the DDT
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Figure 4. GC analysis of extract from a sample of Seveso soil polluted by TCDD added to a solution of ethyl oleate and xylene, purified but before UV irradiation. Column, chromatographic conditions, and peak numbering as in Figure 1
molecule is apparently disrupted. Applications. The analyses of Seveso soil samples and of external and internal house plasters of the contaminated area exposed to UV radiations have been performed with the method here described. Moreover, the analyses related to experiments on the photodecomposition of TCDD of samples of different materials artificially contaminated have been carried out. A comparison with the results obtained by using mass fragmentography gave a random discrepancy of 10 -15%. In Figure 6 a typical application of the gas chromatographic method of analysis is reported. The two curves show the degradation of TCDD contained in the Seveso soil by solar radiation, and the results of an experiment made in a room of a Seveso house by artificial irradiation with a UV lamp as described in the figure caption. It should be pointed out that it is not the aim of this paper to discuss the results obtained with the photodecomposition of TCDD by UV radiation, so that we shall not enter deeply here in these arguments. However, some considerations on the efficacy of the method are to be made. A comparison of Figures 4 and 5 shows that sun radiation in the presence of the ethyl oleate-xylene mixture destroys
ANALYTICAL CHEMISTRY, VOL. 50, NO. 6, MAY 1978
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Figure 5. Chromatogram of the same sample as in Figure 4,but after 5 days of solar irradiation. Column, chromatographic conditions, and peak numbering as in Figure 1
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Flgure 6. Disruption curves of TCDD. (1) Seveso soil spread with a mixture of ethyl oleate and xylene exposed to natural solar radiation. (2) Artificial TCDD sample placed in a room spread with the ethyl oleate-xylene mixture and irradiated with a Philips MLU 300-W lamp. Irradiation power on the sample: 20 p W / c m 2
some of the pesticides identified. p,p'-DDE and Heptaclor are strongly reduced in our experimental conditions and a similar behavior is observed for p,p'-DDT. o,p'-DDD, endrin, o,p'-DDT and p,p'-DDD appear to be little affected. McGuire et al. (12)report that the dechlorination process of Heptachlor takes place only if irradiated (in the presence of hexane or cyclohexane) with short wavelength radiation (253.7 nm). The apparent contrast with our experiments may be explained by the different medium used. Ethyl oleate-xylene apparently shifts the effective wavelength toward higher values (13). Some disagreements between our results and those found by other authors (13) may be ascribed to differences in the experimental conditions, i.e. wavelength and photosensitizers. A noticeable difference is observed in the effectiveness of the method when applied to soil or house walls. This is due to several reasons. A major one is that the smooth walls of
735
the houses are fully exposed to the artificial UV radiation, whose intensity and wavelength have been chosen to obtain the maximum effect. In the case of soil, it should be noted that the degradation reported is referred to a 1-cm depth sample, so that it was surprising to find an effect such as that reported in curve 1 of Figure 6. As UV radiations do not penetrate the soil, but decomposition occurs also a t a considerable extent well below the soil surface, either a diffusion mechanism of TCDD in the oleate medium or photolytic reactions occurring through long life free radicals might be invoked. The initial content of TCDD in soil (100% in Figure 4, curve 1) was 7.0 pg/kg as resulted from the average of ten measurements of the TCDD concentration after homogenization, so that in our experimental conditions a decomposition rate higher than 1 pg/day/kg of soil was obtained. In the light of the results of our study, it can be anticipated that, if the contaminated area would be sprayed with a sufficient amount of xylene-ethyl oleate mixture (150 mL/m2) repetitively within a summer time, decontamination could be performed a t a quite satisfactory extent. I t should be noted that xylene is mainly used as a viscosity reducer, as laboratory experiments show that ethyl oleate is fully effective if used alone. In the case of mapping the polluted area, when few picograms per kilogram of soil must be monitored, our method should be substituted with a more sophisticated technique. However, it can be used as a side method to obtain approximate values of contamination. We feel that this is important because of the extremely reduced cost of the GC apparatus (at least 20 times less than a sophisticated mass spectrometer). In this way, it is possible to multiply the number of analyses that can be carried out, so that the mass spectrometer can be reserved for accurate determinations of lower TCDD levels. Another feature of the method described is that, because of the ease of execution, it may be used by nonhighly specialized personnel.
LITERATURE CITED (1) D. G. Crosby and A. S.Wood, Science, 173, 748 (1971). (2) A. Liberti, "Decontamination of a polluted area by photodegradation of chlorodioxin", paper presented at the International Symposium of Photodegradation of Chlorodioxin, Rome, August 1976. (3) I. Allegrini, G.Bertoni, D. Brocco, and M. Possanzini, Chim. Ind.. 59, 541 (1977). (4) H. R. Buser, Anal. Chem., 48, 1557 (1976). (5) H. R. Buser. Anal. Chem., 49, 918 (1977). (6) L. A. Shadoff and R. A. Hummel, 170th National Meeting, American Chemical Society, Chicago, Ill., 1975,Abstr. Anal. 80. (7) R. Baughman and M. Meseison, Adv. Chem., 120, 92 (1973). (8) Thompson, J. R., Ed., "Analysis of Pesticides in Human and Environmental Samples", U S . EPA-Research Triangle Park, N.C., 1974,Section 9, E, P 4. (9) F. Bruner, P. Ciccioli, and S. Zeili, Anal. Chem., 45, 1002 (1973). (IO) R. Baughman and M. Meselson, Environ. Heakh Perspect., 5 27,(1973). (11) H. R. Buser, J . Chomatogr., 67, 247 (1972). (12) R. R. McGuire, M. J. Zabik, R. D. Shuetz, and R . D. Blotard, J . Agrlc. Food Chem., 18, 319,(1970). (13) See for example: F. Matsmura, in "Environmental Pollution by Pesticides", C. A. Edwards, Ed., Plenum Press, London, New York, 1972 pp 505-506.
RECEIVED for review August 8, 1977. Accepted January 31, 1978.
