Vapor-phase photodecomposition of DDT

Chemosphere No. 4, PP 167 - 172, 1977-

Pergamon Press.

Printed in Great Britain.

VAPOR-PHASE PHOTODECOMPOSITION OF DDT D.G. Crosby and K.W. Moilanen Department of Environmental Toxicology University of California Davis, California 95616 INTRODUCTION (Received in USA 15 December 1976; received in UK for publication 9 March 1977)

Extensive global monitoring over a period of years has confirmed the worldwide presence of DDT in the atmosphere. Although the levels vary widely, and the distinction between vapor and particulate form has been d i f f i c u l t , DDT residues as high as 171 mg/m3 have been reported in the a i r adjacent to application sites. 2 Atmospheric DDT may occur in particulate form as a result of spray d r i f t or blowing dust, but i t s propensity to v o l a t i l i z e assures that much of i t enters a i r as vapor from these sources as well as from leaf, s o i l , and water surfaces. 3 DDE is even more v o l a t i l e and predominates in the a i r over a DDT-treated f i e l d . 4 Previous research shows that photodecomposition of DDT is slow in water5 and on solid surfaces6, although i t s breakdown in organic solvents is more rapid. 7 However, as global modelling estimates a mean atmospheric residence time of four years for atmospheric DDT8, sunlight might play a major part in the environmental destruction of DDT and DDE i f they were photolyzed in the vapor state. 9 MATERIALS AND METHODS Chemicals. Chemical standards and starting materials were of the purest commercial grade, recrystallized i f necessary to provide chromatographic homogeneity. Solvents were r e d i s t i l l e d shortly before use. l-Chloro-2,2-bis(4'-chlorophenyl)ethylene (DDMU) was prepared by alkaline dehydrochlorination of 1,l-dichloro-2,2'-bis(4'-chlorophenyl)ethane(DDD)IO, and 3,5-dichlorofluorenone was provided by J.R. Plimmer(USDA, B e l t s v i l l e , Md.). Irradiation.

Experiments were conducted in 72-1iter borosilicate glass photoreactors at

approximately room temperature and normal atmospheric pressure.

The desired compound (5 mg)

was evaporated from a coated watch-glass by application of gentle heating (about 35tC) from 167

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No. 4

outside the flask to furnish a saturated atmosphere. A collimated light beam, 5 cm in diameter, from an RS Sunlamp (General Electric Co.), was filtered through a borosilicate glass window into the reaction chamber; dark controls were identical except that the light was not turned on.

In

another control, the light was reflected back onto the reactor's inner wall by means of an external mirror.

II

After 96 hrs, the contents of the flask were extracted by sequentially adding five 400 ml. portions of hexane, shaking, and then reducing the combined rinses to a small volume on a rotary evaporator. The residual extract was analyzed by combined gas chromatography-mass spectrometry (GC-MS) which employed a Finnigan Model 3000 Peak Identifier equipped with a 5 f t . x I/8 in i.d. glass column containing 2% OV-I on 60/80 mesh, acid-washed, DMCS-treated Chromosorb G (Perco Supplies, San Gabriel, C a l i f . ) .

The i n i t a l column temperature was 150°C, final column tempera-

ture 270°C, program rate lO°C per min, and helium carrier gas at 16 ml/min. As each compound eluted, its mass spectrum was recorded and quantitated by comparison with authentic standards. Ambient air samples were collected from Davis, California in ethylene glycol at about lO ~/min with a standard Greenberg-Smith impinger12, and the hexane extracts were analyzed by electron capture gas chromatography (EC-GC). EC-GCanalysis employed a Varian Aerograph Model 2100 equipped with the glass column described above, column temperature 210°C, injection port temperature 265°C, detector temperature 215°C, and nitrogen carrier gas at 20 ml/min. RESULTS AND DISCUSSION The ultraviolet (uv) irradiation of DDT (l,l,l-trichloro-2,2-bis(4'-chlorophenyl)ethane) vapor (Table I) resulted primarily in the formation of DDE, (l,l-dichloro-2,2-bis(4'-chlorophenyl)ethylene) with much smaller amounts of DDD and traces of other volatile substances. The proportions were largely the samewhether the reactor wall was irradiated or not. The " h a l f - l i f e " of DDT was about 6 days, but DDD vapor appeared stable to light. Table I.

Vapor-PhasePhotoproducts from p,p'-DDTa p~p'-DDE(mg)

p,p'-DDD(mg)

p,p'-DDT(mg)

Irradiated vapor

1.3

O.l

3.4

Irradiated vapor and walls

].5

O.l

3.2



5.0

Dark control

a5 mg of p,p'-DDT was irradiated for 4 days.

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169

DDE vapor decomposed relatively slowly in light to give primarily DDMUand DCB (4,4'dichlorobenzophenone) (Table I I ) , although small proportions of at least 7 other products were observed by EC-GC. Three of these had retention times and mass spectra qualitatively identical with those of 4,4'-dichlorobiphenyl, 2,4,5-trichlorobiphenyl, and 2,2',5,5'-tetrachlorobiphenyl, but exact identification of isomers was not possible. Table II.

Vapor-Phase Photoproducts from p,p'-DDEa Amount (pg)a

M+(m/e)

Formula

Identity

222

CI2H8CI2 Dichlorobiphenyl

236

CI2H6CI20

250

Light b

Dark

20

<2

2

<2

CI3H8CI20 DCB

60

3

250

C13H8C120 DCB isomer

20

<2

256

CI2H7CI 3

Trichlorobiphenyl

2

<2

282

C14H9C13

DDMU

40

<2

2B2

CI4H9CI3

DDMUisomer

20

<2

290

CI2H6CI 4

Tetrachlorobiphenyl

5

<2

316

CI4H8CI 4

DDE isomer

30

<2

316

CI4H8CI 4

DDE

4800

5000

a5 mg of p,p'-DDE was irradiated for 4 days. bproduct distribution was essentially identical when the reflector was used, except that 120 ~g of 3,6-dichlorofluorenone was formed and 4600 ~g of DDE remained. The third most abundant product exhibited a mass spectrum identical to that of DDE, but its retention time differed slightly.

A similar DDMUisomer (m/e 282) also was present. Kerner

et al. 13 reported that the NMR spectrum of the DDE photoisomer they isolated showed i t to be a dichlorophenyl homolog of DDMU,and Wolfe et al. 14 have shown the DDE photoisomer formed in hexane or water5 to be l-chloro-2-(4'-chlorophenyl)-2-(2',4'-dichlorophenyl)ethylene.

Two other

oxygenated products were present, one an isomer of DCB and the other, CI2H6CI20, possibly a dichlorodibenzofuran. 15 No 3,6-dichlorofluorenone was formed from DDE vapor, but i t was the major photoproduct when DDE was irradiated on the reactor wall. 16

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170

Cl !

H-C-CI

C,I CI'C'CI

FFC-Cl

l

L

Cl-C-Cl

H

Cl Figure I.

CI

Vapor-Phase Photochemical Transformations of p,p'-DDT and its Photoproducts.

Irradiation of DDMUin the photoreactor gave primarily DCB, while DCB in turn slowly formed dichlorobiphenyl;

the chlorinated biphenyls were stable to irradiation in the vapor phase. The

photochemical formation of simple chlorobiphenyls from DDT or DDE in solution has been observed in several previous investigations 7'16'17, perhaps from decarbonylation of chlorinated fluorenones (although 3,6-DCF was photochemically unreactive under our conditions).

That they do not

occur appreciably in environmental samples18 must be due both to their v o l a t i l i t y 19 and to their

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171

rapid photodecomposition in solution. 15'20 The photochemical generation of a more stable isomer having properties very similar to those of DDE may prove to have greater environmental s i g n i f i cance. Ambient a i r samples from Davis, California, provided gas chromatograms with peaks corresponding to those of DDT, DDD, DDE (or i t s isomer) and DCB, but amounts were too small for mass spectrometric identification or unambiguous identification of PCB (polychlorinated biphenyl) isomers. Our results, which were similar to those of Korte's group13 who irradiated DDE vapor under quite different conditions, are summarized in Fig. I.

However, both our experiments and theirs

probably represent only gross approximations of the real atmospheric environment. DDE concentrations were too high, atmospheric oxidants other than oxygen were essentially excluded, the wavelength range of irradiation was very limited, and wall reactions--although minimized in our reactor--were not precluded. The probable intervention of walls in DDD and DDE formation, the lack of oxygenated products from DDT photolysis, and the formation of the DDE isomer require further attention.

However, i t seems certain that DDE vapor photodecomposition w i l l predominate

in this series.

ACKNOWLEDGEMENT This research was supported in part by NSF grant BMS74-I1783 and USDA Regional Research Project W-45. A review of the original presentation 9 was published by T. Maugh.21 LITERATURE CITED I.

C.A. Wheatley, in "Environmental Pollution by Pesticides" (C.A. Edwards, ed), Plenum Press, London, 1973, p. 365.

2.

J.T. Middleton, in "Research in Pesticides" (C.O. Chichester, ed), Academic Press, New York, 1965, p. 191.

3.

W.F. Spencer, Residue Reviews 59, 91 (1975). ~

~

4.

M.M. Cliath, W.F. Spencer, Environ. Sci. Technol. 6, 91O (1972).

5.

J.T. Leffingwell, "Photolysis of DDT in Water," Thesis, University of California, Davis,

~

1975. 6.

H.J. Wichmann, W.I. Patterson, P.A. Clifford, A.K. Klein, H.V. Claborn, J. Ass. Off. ABr. Chemists 29, 218 (1946). ~ ~

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7 .

J.R. Plimmer, U.I. Klingebiel, B.E. Hummer, Science 167, 67 (1970).

8.

G.M. Woodwell, P.P. Craig, H.A. Johnson, Science 174, llOl (1971).

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9.

K.W. Moilanen, D.G. Crosby, Abstr. 165th Meeting~ Amer. Chem. Soc., Dallas, Texas, April, 1973, Pest 21.

I0.

E.C. Horning, Organic Syntheses, Collective Volume I I I , 270 (1962).

II.

D.G. Crosby, K.W. Moilanen, Arch. Environ. Contam. Toxicol. 2, 62 (1974).

12.

J.W. Miles, L.E. Fetzer, G.W. Pearce, Environ. Sci. Techno1. 4, 420 (1970).

13.

I. Kerner, W. Klein, F. Korte, Tetrahedron 28, 1575 (1972).

14.

N.L. Wolfe, R.G. Zepp, D.F. Paris, G.L. Baughman, R.C. Hollis, Abstr. 172nd Meeting, Am.

~

~ ~

Chem. Soc., San Francisco, September, 1976, Pest 109. 15.

D.G. Crosby, K.W. Moilanen, Bull. Environ. Contam. Toxicol. I0, 372 (1973). ~ ~

16.

J.R. P1immer, U.I. Klingebiel, Chem. Commun. 648 (1969).

17.

J.T. Leffingwell, D.G. Crosby, Unpublished data, 1970.

18.

D.B. Peakall, J.L. Lincer, Bioscience 20, 958 (1970).

19.

D. MacKay, P.J. Leinonen, Environ. Sci. Technol. 4, 420 (1970).

~ ~

~

20.

L.O. Ruzo, K.M.J. Sab, R.D. Schuetz, Bull. Environ. Contam. Toxicol. 8, 217 (1972).

21.

T.H. Maugh, Science 180, 578 (1973).

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