TCDD Solubilization and Photodecomposition in Aqueous Solutions Claudio Botre', Adriana Memoli, and Franco Alhaique Cattedra di Chimica Fisica, Centro di Chimica del Farmaco, Facolta di Farmacia, Universita di Roma, Rome, Italy
The solubilization and photodecomposition of 2,3,7,8tetrachlorodibenzoparadioxin (TCDD) in aqueous solutions of cationic, anionic, and nonionic surfactants are described. A cationic surfactant, 1-hexadecylpyridinium chloride, acts as an energy transfer agent in the photodecomposition process, thus increasing the TCDD decomposition rate. Samples of material from Seveso's contaminated area are treated according to the proposed decontamination method, and results are discussed. On July 10, 1976, a wide area near Seveso, Italy, was contaminated by an extremely toxic fallout consisting of 2,3,7,8-tetrachlorodibenzoparadioxin(TCDD) in a chemical mixture of other chloroorganic substances ( I , 2). The decontamination of soil, buildings, personal belongings, and other different materials from TCDD is difficult, not only because of the extremely high toxicity of such a substance, but also because of the peculiarities of this product, which is chemically refractory and insoluble in water. Although much work has been done in this particular field, only three different techniques for decontamination from this kind of pollutant have been proposed: incineration, chlorinolysis, and soil biodegradation ( 3 ) .Although the first method is undoubtedly the safest as far as complete TCDD destruction is concerned, the use of very high temperatures (-1000 "C) does not allow any recovery of contaminated materials. Chlorinolysis is also a destructive method involving high chlorine pressures and temperatures for conversion of organic compounds to carbon tetrachloride. The third option appears to be the most promising technique; however, it is now feasible only for cultivable soils. Therefore, we are seeking an alternative decontamination method that is simple, inexpensive, and effective. Our method would allow the recovery of contaminated materials treated with aqueous solutions, and the photodecomposition of both TCDD and the solubilizing agent. T o date, photodecomposition is the most rapid method of TCDD degradation. This is achieved by an energy transfer mechanism. Micellar solubilization of TCDD in the water medium has been studied, and significant results have been obtained. Among the different surfactants used for these experiments, l-hexadecylpyridinium chloride (CPC) appears to be the most effective because of enhanced solubilizing properties and faster photochemical degradation of TCDD in this micellar solution.
Materials and Methods
A pure sample of TCDD was supplied by Rochester University, New York, to Istituto Superiore di SanitA, Rome, Italy. All surfactants and reagents were of analytical grade. UV measurements were carried out with a Beckman DU-2 spectrophotometer, using quartz cells having a path length of 10 mm. A Desaga Uvis UV lamp (254-356 nm) was used for photodecomposition experiments. (Since the relative effect of the solubilizing solution was the aim of photochemical degradation studies, no absolute value of light intensity was determined). Isolation and identification of TCDD were performed according to the method proposed by Camoni's research team of the Istituto Superiore di SanitB, Rome ( 4 ) ; and quantitative determinations were carried out by gas chromatography-mass spectrometry techniques using a Hewlett-Packard 5980 A instrument (GC operating condi0013-936X/78/0912-0335$01 .OO/O
0 1978 American Chemical Society
tions: 4-ft column 3% OV-17 on 100/120 chromosorb W-HP; inlet temperature, 300 "C; column temperature, 240 "C; separator temperature, 240 "C). For TCDD solubilization from soil, experiments were performed with 90-g homogeneous samples from Seveso's contaminated area. Samples were treated twice with 300 mL of solubilizing solution and then three times with the same amount of water to remove the surfactant. The residues were finally extracted with methanol and benzene, and TCDD was determined in the obtained solutions. Untreated contaminated soil samples were used as reference standards. These experiments were set up with the following solvent solutions: 0.05 M sodium dodecyl sulfate (SDS), 0.05 M l-hexadecylpyridinium chloride, 2% w/v polyoxyethylene sorbitan monooleate (Tween go), and methanol. Parallel solubilization studies were carried out on pure TCDD: samples of 5 and 12 mL of a benzenic solution of TCDD (8.18pg/mL) were vacuum evaporated, and the residues were treated, respectively, with 4 mL of the test solvent solution (0.02,0.05, and 0.08 M SDS; 0.02, 0.05, and 0.08 M CPC; 0.02, 0.05, and 0.08 M hexadecyltrimethylammonium bromide CTAB; 1, 2, and 3% w/v Tween 80) and kept in a dark place a t room temperature and checked periodically for UV absorbance until equilibrium was reached (48 h); methanol was used as a reference solvent for these dissolution tests.
Results and Discussion Results obtained from solubilization experiments on soil and pure TCDD are reported in Table I. In soil experiments, CPC appears to be the best solubilizing aqueous agent among the other surfactant solutions. With pure TCDD only slight differences can be observed; nevertheless, good qualitative agreement can be observed for the two sets of experiments. The more effective solubilization of the pollutant in the cationic detergent (more evident for experiments on soil) can be related to the more compact structure of cationic detergent micelles when compared to the anionic ones ( 5 ) and to the nature of TCDD molecules. But the main and more interesting differences among the micellar solutions of the tested surfactants are related to TCDD decomposition; in fact, micellar solutions of TCDD are stable when stored in the dark, whereas solubilized TCDD can be decomposed when exposed to sunlight or to UV irradiation. Photodecomposition data for different solutions are given in Figure 1 where the percentage of undecomposed TCDD in solution is plotted as a function of time of irradiation. Here the rate of photodecomposition in CPC micellar solution is evident. In our experimental conditions the time required for total TCDD decomposition is only 4 h for CPC solutions, whereas 8 h are required for SDS solutions and about 18 h when the best solvent (MeOH) is used. TCDD photodegradation can be spectrophotometrically observed. The absorption maximum of TCDD rapidly disappears after UV exposure, and a t the same time a new maximum a t 278 nm can be observed. This is coincident with the absorption of 2phenoxyphenol, the last step photodegradation product of TCDD ( I ) . An appreciable turbidity was observed when 98.16-pg samples were used for dissolution tests. This can be related to the properties of surfactants that are both solubilizing and wetting agents. Therefore, substances like TCDD, which are water insoluble, may enhance their solubility when taken up Volume 12, Number 3, March 1978 335
Table 1. Solubilization of TCDD
Solublllzer
Experiments on soila SolublSurfactant lized TCDD concn (%)
MeOH
...
CPC
0.05 M 0.05 M 2 % WIV
SDS Tween 80
Surfactant concn
...
97.5 75.0 60.0 45.0
Each 90-g sample contained initially 6.3 pg of TCDD. and CPC.
-
0.02 M 0.02 M 1 % WIV
c
7
time ihl
Figure 1. Degradation of TCDD
as a function of time in different sol-
vents Plot a: 0.02 M CPC solution: plot b: 0.02 M SDS solution; plot c: methanol. Initial concentration of TCDD: 8.0 pglmL
by micelles and can also be more easily dispersed because of the interaction with surfactant monomers. Furthermore, when such turbid micellar solutions of TCDD are exposed to UV irradiation, they clear quite rapidly. Such effects can be related to the observation that only TCDD in solution can be decomposed by light (6); therefore, as dioxin degradation proceeds, more substance is solubilized within surfactant micelles. The reason for the faster photodecomposition of TCDD in CPC micellar solution is not completely known a t the present time; however, we have observed that the molecular structure of CPC decomposes after UV exposure, and a new sharp absorption maximum appears a t 374 nm. Also, when TCDD is enclosed in micelles, degradation of CPC is sharply reduced.
336 Environmental Science & Technology
100 75 71 72
... 0.05 M 0.05 M 2 % WIV
Solublk e d TCDD (% )
100 78
75 73
Initial amount of TCDD: 40.90 pg. CTAB solubilizing capacity is between that of the anionic surfactant
-1
e
Experiments on pure TCDDb Solublllzed TCDD Surfactant (%) concn
This can be interpreted in terms of a stabilizing interaction between the surfactant and TCDD molecules; it appears reasonable to suppose that T - T interactions between the pyridine ring and aromatic TCDD system take place, leading to an energy transfer from one molecule to the other, which enhances the photodecomposition rate of “hound” TCDD. Further investigation on this reaction mechanism is still in progress in our laboratory. In conclusion, this method seems to be appropriate and effective for the decontamination of buildings, furniture, and personal belongings from TCDD. Its application to soil decontamination should involve the use of the same techniques applied in mineral dressing procedures and, if requested, in repeated “washing” treatments. A worthwhile feature of this method is the possibility of a rapid photodecomposition of an aqueous detergent solution with the simultaneous degradation of both the solubilizing and the polluting agents.
Acknowledgment The authors thank the Istituto Superiore di SanitA of Rome for the kind hospitality, technical assistance, and interest in this work. Literature Cited (1) Gribble, G. W., Chemistry, 47 (2), 15 (1974). (2) Hay, A,, Nature, 262,636 (1976). (3) Kearney, P. C., Woolson, E. A., Isensee, A. R., Helling, C. S., Enuiron. Health Perspect., 5,273 (1973). (4) Camoni, I., Di Muccio, A,, Pontecorvo, D., Vergori, L., Communication on TCDD determination Rapp. ISTISAN 1977/3, Istituto Superiore di Sanitl, Rome, Italy. ( 5 ) Fendler, J. H., Fendler, E. J., in “Catalysis in Micellar and Macromolecular Systems”, Academic Press, New York, N.Y., 1975. (6) Crosby, D. G., Wong, A. S., Plimmer, J. R., Woolson, E. A., Science, 713,748 (1971).
Receiced for review March 7, 1977. Accepted September 28, 1977. Work supported by a C N R research grant.
