dioxins - ACS Publications

6

Photochemistry of Dibenzo-p-dioxins

JACK R. P L I M M E R and U T E I. K L I N G E B I E L Plant Science Research Division, Agricultural Research Service, U. S. Department of Agriculture, Beltsville, Md. 20705

Downloaded by COLUMBIA UNIV on March 31, 2013 | http://pubs.acs.org Publication Date: March 1, 1973 | doi: 10.1021/ba-1973-0120.ch006

D O N A L D G . CROSBY and A N T H O N Y S. W O N G Department of Environmental Toxicology, University of California, Davis, Calif. 95616

Chlorinated

dibenzo-p-dioxins

are contaminants of phenol

-based pesticides and may enter the environment where they are subject to the action of sunlight.

Rate

measurements

showed that 2,3,7,8-tetrachlorodibenzo-p-dioxin more rapidly

photolyzed

benzo-p-dioxin. zo-p-dioxin,

Initially TCDD

and

accompanied

in methanol

subsequent

by ring fission.

than

(TCDD)

yields 2,3,7-trichlorodibenreductive

dechlorination

Pure dibenzo-p-dioxin

polymeric material and some 2,2'-dihydroxybiphenyl radiation.

is

octachlorodi-

Riboflavin-sensitized

is

gave on ir-

photolysis of the potential

precursors of dioxins, 2,4-dichlorophenol and 2,4,5-trichlorophenol, in water gave no detectable dioxins.

The

identified were chlorinated phenoxyphenols and biphenyls.

products

dihydroxy-

In contrast, aqueous alkaline solutions of purified

pentachlorophenol gave traces of

octachlorodibenzo-p-dioxin

on irradiation.

" p e s t i c i d e s derived f r o m chlorinated phenols ( T a b l e I ) are among the •*· most p r o m i n e n t o f those c u r r e n t l y i n w o r l d w i d e use. S e v e r a l major h e r b i c i d e s h a v e b e e n a p p l i e d i n large q u a n t i t i e s i n s u b t r o p i c a l locations. C a l i f o r n i a u s e d m o r e t h a n 1,200,000 p o u n d s of 2 , 4 - d i c h l o r o p h e n o x y a c e t i c a c i d ( 2 , 4 - D ) a n d its d e r i v a t i v e s i n 1970 ( I ) ; H a w a i i c o n s u m e d some 465,000 p o u n d s o f p e n t a c h l o r o p h e n o l ( P C P ) i n 1968 ( 2 ) , a n d t h e a m o u n t of c o m b i n e d b u t y l esters o f 2 , 4 - D a n d 2 , 4 , 5 - t r i c h l o r o p h e n o x y a c e t i c a c i d ( 2 , 4 , 5 - T ) released i n o n e area o f C a m b o d i a d u r i n g t w o m o n t h s o f 1969 w a s e s t i m a t e d t o exceed 77,000 p o u n d s ( 3 ) . 44

In Chlorodioxins—Origin and Fate; Blair, E.; Advances in Chemistry; American Chemical Society: Washington, DC, 1973.

6.

P L I M M E R

Photochemistry of Dioxins

E T A L .

Table I.

45

Some Pesticides Based on Polychlorophenols

Common Name (Use)

Chemical Name

2 , 4 - D (herbicide) 2 , 4 - D B (herbicide) N i t r o f e n (herbicide) G e n i t e (acaricide) Z y t r o n (herbicide)

2,4-E>ichlorophenoxyacetic a c i d 4-(2',4'-Dichlorophenoxy) butyric acid 2 , 4 - D i c h l o r o p h e n y l 4 - n i t r o p h e n y l ether 2 , 4 - D i c h l o r o p h e n y l benzenesulfonate 0-(2',4'-Dichlorophenyl) 0-methyl isopropylphosphoramidothioate 2 , 4 , 5 - T (herbicide) 2,4,5-Trichlorophenoxyacetic acid S i l v e x (herbicide) 2-(2',4',5 -Trichlorophenoxy) propionic acid E r b o n (herbicide) 2-(2 ,4',5'-Trichlorophenoxy) ethyl 2,2-dichloropropionate R o n n e l (insecticide) 0,0-Dimethyl 0-2,4,5-trichlorophenyl phosphorothioate G a r d o n a (insecticide) 2-Chloro-l-(2 ,4 ,5 -trichlorophenyl)v i n y l d i m e t h y l phosphate P C P (herbicide, insecticide), P e n t a c h l o r o p h e n o l wood preservative ,


,

,

,

,

V a r i a t i o n s i n the m a n u f a c t u r i n g process of 2,4,5-trichloro- a n d p e n t a chlorophenol ( b u t not 2,4-dichlorophenol)

h a v e sometimes

resulted i n

c o n t a m i n a t i o n o f the p r o d u c t b y s m a l l amounts o f h e t e r o c y c l i c i m p u r i t i e s (4,5). O f these, the c h l o r i n a t e d d i b e n z o - p - d i o x i n s s u c h as T C D D (2,3,7,8t e t r a c h l o r o d i b e n z o - p - d i o x i n ) h a v e r e c e i v e d m u c h scientific a n d p u b l i c a t t e n t i o n because o f t h e i r r e a l o r p o t e n t i a l t o x i c i t y (6,7).

[ C h i c k edema

factor, a c u r i o u s t o x i c o l o g i c a l p r o b l e m to p o u l t r y p r o d u c e r s f o r several years, has b e e n s h o w n t o b e c o m p o s e d of c h l o r o d i b e n z o - p - d i o x i n s ( 8 ) . ] P h e n o l - b a s e d pesticides m a y b e a p p l i e d as f o l i a r sprays o r o t h e r w i s e enter t h e e n v i r o n m e n t w h e r e t h e y b e c o m e subject to t h e a c t i o n o f s u n l i g h t (7, 8, 9, 10).

C o n s e q u e n t l y , their c o n t a i n e d d i o x i n s also w i l l b e

exposed t o sunlight. T h e present s t u d y determines t h e extent, c o n d i t i o n s , a n d p r o d u c t s o f their p h o t o d e g r a d a t i o n . 2,4,5-T a n d 2 , 4 - D are d e g r a d e d i n s u n l i g h t t o a m i x t u r e o f p r o d u c t s i n w h i c h t h e p a r e n t p h e n o l is p r o m i nent (9,10).

T h e p o s s i b i l i t y that c h l o r i n a t e d phenols m i g h t f o r m d i o x i n s

b y t h e a c t i o n o f s u n l i g h t , as t h e y d o b y t h e r m a l r i n g closure, also w a s investigated. T h e p h o t o l y s i s o f c h l o r i n a t e d a r o m a t i c c o m p o u n d s occurs b y several processes w h i c h f o l l o w p r e d i c t a b l e routes (13). T h e y f r e q u e n t l y u n d e r g o p h o t o c h e m i c a l loss o f c h l o r i n e b y d i s s o c i a t i o n o f the e x c i t e d m o l e c u l e t o free r a d i c a l s or, a l t e r n a t i v e l y , t h r o u g h a n u c l e o p h i l i c d i s p l a c e m e n t reac t i o n w i t h a solvent o r substrate m o l e c u l e . E i t h e r m e c h a n i s m is p l a u s i b l e , a n d t h e o p e r a t i o n o f one o r t h e other m a y b e i n f l u e n c e d b y t h e r e a c t i o n m e d i u m a n d t h e presence o f other reagents.


46

CHLORODIOXINS

ORIGIN

AND

FATE

I n d i l u t e s o l u t i o n , the structure of the u l t r a v i o l e t ( U V ) i r r a d i a t i o n p r o d u c t s d e p e n d s o n the solvent.

I n m e t h a n o l , o - c h l o r o b e n z o i c a c i d is

p h o t o r e d u c e d q u i t e r a p i d l y to b e n z o i c a c i d , w h e r e a s a m i x t u r e of s a l i c y l i c a n d b e n z o i c acids forms s l o w l y i n w a t e r ; h o w e v e r , i n b e n z e n e the p r o d u c t is 2 - p h e n y l b e n z o i c a c i d . m - C h l o r o b e n z o i c a c i d reacts m u c h m o r e s l o w l y t h a n the o-isomer u n d e r the same c o n d i t i o n s , a n d a b e n z o i c a c i d c o n t a i n i n g ortho- a n d m e f a - c h l o r i n e atoms w i l l u n d e r g o p r e f e r e n t i a l loss of the ortho substituent (14,

A l t h o u g h the f a c i l e p h o t o l y t i c r e d u c t i o n

15).

of h a l o g e n a t e d a r o m a t i c c o m p o u n d s i n m e t h a n o l a n d other alcohols has p r e p a r a t i v e v a l u e a n d has b e e n i n v e s t i g a t e d b y several w o r k e r s (16, Downloaded by COLUMBIA UNIV on March 31, 2013 | http://pubs.acs.org Publication Date: March 1, 1973 | doi: 10.1021/ba-1973-0120.ch006

d e t a i l e d correlations b e t w e e n

p o s i t i o n a n d ease-of-loss of the

17),

chlorine

substituent a n d the effect of other substituents o n the r e a c t i o n h a v e not b e e n r e p o r t e d . W e m u s t r e c o g n i z e that s u c h p h o t o c h e m i c a l t r a n s f o r m a tions i n v o l v e a n e x c i t e d state a n d not the ground-state

electronic

dis

t r i b u t i o n to w h i c h H a m m e t t f u n c t i o n s are a p p l i c a b l e . The

Photolysis of

Dioxins

T h e b i o l o g i c a l a c t i v i t y of several h a l o g e n a t e d h e r b i c i d e s i n w a t e r is d e s t r o y e d b y u l t r a v i o l e t i r r a d i a t i o n (18). promising method for decontaminating

I r r a d i a t i o n seems to b e a

s m a l l quantities

of

pesticides.

T h e c h e m i c a l s i m i l a r i t y b e t w e e n the c h l o r i n a t e d d i o x i n s a n d other c h l o rinted aromatic their

compounds

photochemical

suggested

behavior,

that if there w e r e parallels i n

s u n l i g h t m i g h t destroy

dioxins i n

the

environment. 2 , 3 , 7 , 8 - T e t r a c h l o r o d i b e n z o - p - d i o x i n ( T C D D ) ( I ), a n o c c a s i o n a l c o n t a m i n a n t i n 2,4,5-T a n d other t r i c h l o r o p h e n o l d e r i v a t i v e s , is the t o x i c of the c o m m o n l y - e n c o u n t e r e d d i o x i n s (8)

most

a n d i t r e c e i v e d m o s t of

o u r attention. Its l o w s o l u b i l i t y i n c o m m o n solvents a n d w a t e r ( ca. 2 p p b ) l i m i t e d o u r experiments since the p r o d u c t s w e r e d i f f i c u l t to i d e n t i f y b y the c o n v e n t i o n a l t e c h n i q u e s of o r g a n i c c h e m i s t r y .

However, T C D D

a n a b s o r p t i o n m a x i m u m at 307 n m i n m e t h a n o l — w e l l w i t h i n the

has solar

s p e c t r u m o b s e r v e d at the earth's surface a n d near the r e g i o n of m a x i m u m intensity ( 3 1 0 - 3 3 0 n m ) of the U V l a m p s u s e d i n p r e v i o u s (14, 19).

experiments

T h e p h o t o l y s i s rate of several c h l o r i n a t e d d i o x i n s w a s d e t e r m i n e d i n m e t h a n o l (20)

(Figure 1).

Solutions of 2 , 7 - d i c h l o r o d i b e n z o - p - d i o x i n (5

m g / l i t e r ) , T C D D ( 5 m g / l i t e r ) , a n d o c t a c h l o r o d i b e n z o - p - d i o x i n (2.2 m g / l i t e r ) w e r e i r r a d i a t e d w i t h l i g h t h a v i n g a n i n t e n s i t y of a b o u t 100 /xW/cm


2


6.

P L I M M E R

E T

A L .


47

Irradiation (hours) Science

Figure 1. Photolysis rates of chlorinated dibenzo-p-dioxins in methanol under ultraviolet light: 2,7-dichlorodibenzo-p-dioxin (III) (5 mg/liter), 2,3,7,8-tetrachlor odibenzo-p-dioxin (I) (5 mg/liter), 1,2,3,4,6,7,8,9octachlorodibenzo-p-dioxin (IV) (2.2 mg/ liter) ( 2 0 ) , © 1971 by AAAS at the a b s o r p t i o n m a x i m u m of T C D D ( 307 n m ). P h o t o l y s i s w a s p e r f o r m e d i n sealed b o r o s i l i c a t e glass vessels, a n d t h e c o n c e n t r a t i o n d e t e r m i n e d b y gas c h r o m a t o g r a p h y ( G L C ) .

change w a s

A s expected, r e d u c t i v e d e

c h l o r i n a t i o n o c c u r r e d d u r i n g i r r a d i a t i o n , a n d as the tetra- or o c t a c h l o r o compounds observed.

d i s a p p e a r e d , peaks TCDD

afforded

of shorter

G L C retention

2,3,7-trichlorodibenzo-p-dioxin

times

were

which was

i d e n t i f i e d b y G L C c o u p l e d to a mass spectrometer ( G C / M S ) ( F i g u r e 2 ) . A d i c h l o r o d i b e n z o - p - d i o x i n also w a s f o r m e d i n l o w y i e l d . Octachlorodibenzo-p-dioxin was photolyzed m u c h more slowly than T C D D ( F i g u r e 1 ). T h e rate of d i o x i n photolysis increased as t h e n u m b e r of substituent c h l o r i n e atoms decreased.

O c t a c h l o r o d i b e n z o - p - d i o x i n gave

w h a t seemed to b e a series o f c h l o r i n a t e d d i o x i n s of d e c r e a s i n g c h l o r i n e content

(20).

S i m i l a r results w e r e o b t a i n e d w h e n T C D D i n m e t h a n o l w a s exposed to n a t u r a l s u n l i g h t i n sealed b o r o s i l i c a t e glass tubes or beakers 3).

(Figure

A f t e r about 36 hours exposure, a y e l l o w n o n - v o l a t i l e g u m w a s o b

t a i n e d as t h e sole p r o d u c t b y e v a p o r a t i o n of t h e solvent.

It s h o w e d n o

U V a b s o r p t i o n a n d d i d n o t seem to r e t a i n t h e b e n z e n o i d c h r o m o p h o r e ;


48

CHLORODIOXINS

ORIGIN

AND FATE


10.0 ρ

4 6 Irradiation (hours) Science

Figure 2. Photoreduction of 2,3,7,8-tetrachlorodibenzo-p-dioxin (I) (2 mg/liter in methanol) as com pared with that of the 2,3,7-trichloro-homolog (II) (20), © 1971 by AAAS 100

2

4

6

Irradiation (hours) Science

Figure 3. Photolysis rate of 2,3,7,8-tetrachlorodibenzo-p-dioxin (5 mg/liter in meth anol) in sunlight ( 2 0 ) , © 1971 by AAAS


6.

P L I M M E R

E T

A L .


49

since u n s u b s t i t u t e d d i b e n z o - p - d i o x i n shows a s t r o n g a b s o r p t i o n m a x i m u m at 290 n m i n m e t h a n o l , i t w a s n o t present as a r e a c t i o n p r o d u c t . It seems that deep-seated c l e a v a g e of the d i o x i n n u c l e u s m u s t a c c o m pany dechlorination i n methanol. irradiated i n cyclohexane

W h e n pure dibenzo-p-dioxin ( II ) was

s o l u t i o n i n a q u a r t z cuvette,

it darkened i n

color, a n d a p r e c i p i t a t e of i n t r a c t a b l e d a r k b r o w n m a t e r i a l w a s c o l l e c t e d a n d w a s i n s o l u b l e i n the c o m m o n solvents except f o r m e t h a n o l . A more concentrated

(1000 p p m ) s o l u t i o n of d i b e n z o - p - d i o x i n i n

m e t h a n o l w a s i r r a d i a t e d f o r 1.5 h o u r s u n d e r a 450-watt l a m p fitted w i t h a b o r o s i l i c a t e glass filter w h i l e n i t r o g e n w a s b u b b l e d c o n t i n u o u s l y t h r o u g h , Downloaded by COLUMBIA UNIV on March 31, 2013 | http://pubs.acs.org Publication Date: March 1, 1973 | doi: 10.1021/ba-1973-0120.ch006

the s o l u t i o n . of 8 5 % .

U n c h a n g e d starting m a t e r i a l w a s r e c o v e r e d to the extent

T h e p r i n c i p a l photolysis product again was a dark b r o w n

i n s o l u b l e g u m s i m i l a r to that d e s c r i b e d above.

Its m o b i l i t y o n t h i n layer

c h r o m a t o g r a p h y ( T L C ) w a s v e r y l o w i n the b e n z e n e / e t h y l acetate ( 4 : 1 ) solvent u s e d to separate the other p r o d u c t s . U n d e r U V l i g h t a t y p i c a l c h r o m a t o g r a m s h o w e d starting m a t e r i a l , a p o l y m e r i c substance, a n d t w o m o b i l e c o m p o u n d s w h i c h w e r e

isolated

b y p r e p a r a t i v e T L C . T h e m o r e m o b i l e c o m p o u n d has y e t to b e i d e n t i f i e d , b u t the mass s p e c t r u m of the least m o b i l e ( R 0.52 ) s h o w e d the m o l e c u l a r f

i o n at m/e 186 a n d f r a g m e n t ions at 168 ( M - 1 8 ), 158 ( M - 2 8 ), 157 ( M - 2 9 ), a n d 139 ( M - 2 9 - 1 8 ) . T h e m o l e c u l a r w e i g h t of 186 c o r r e s p o n d e d to either a phenoxyphenol or dihydroxybiphenyl; methylation w i t h gave a c o m p o u n d w i t h m/e

diazomethane

214 ( 186 — 2 H -f- t w o m e t h y l groups ) ac

c o m p a n i e d b y f r a g m e n t ions at m/e 185 ( M - 2 9 ) , 169 ( M - 4 5 ), 168 ( M - 4 6 ) , a n d 157 ( M - 5 7 ) .

Since i t gave a d i m e t h y l d e r i v a t i v e w i t h d i a z o m e t h a n e ,

this p r o d u c t m u s t b e a d i h y d r o x y b i p h e n y l , a n d its i d e n t i t y w a s c o n f i r m e d b y c o m p a r i n g its c h r o m a t o g r a p h i c

properties a n d mass s p e c t r u m

with

those of a n a u t h e n t i c s p e c i m e n o f 2 , 2 ' - d i h y d r o x y b i p h e n y l ( I V ) ( F i g u r e 4 ).

OH

OH Figure 4.

Irradiation of pure dibenzo-p-dioxin

W h e n the crude reaction mixture was examined b y G C / M S , a n addi t i o n a l c o m p o u n d w i t h m/e

186, w h i c h gave a m o n o m e t h y l ether, w a s


50

CHLORODIOXINS

d e t e c t e d i n trace amounts.

ORIGIN

T h i s corresponds to the e x p e c t e d

p h e n o l ( I I I ) , the i n i t i a l p r o d u c t of r i n g o p e n i n g ( F i g u r e T h e photolytic rearrangement

The

(21).

r e a c t i o n p r o c e e d e d t h r o u g h ether b o n d fission f o l l o w e d b y w h i c h recombined

2-phenoxy-

4).

a n d it w a s suggested

intramolecular rearrangement

to g i v e h y d r o x y l a t e d b i -

p h e n y l s . A trace of p h e n o l w a s also o b t a i n e d . dependent,

FATE

of d i p h e n y l ether to o- a n d p - p h e n y l -

p h e n o l has b e e n d e s c r i b e d b y O g a t a et al. of the r a d i c a l fragments

A N D

T h e yields were

solvent

that f o r m a t i o n of a h y d r o g e n

bond

f r o m the a l c o h o l solvent to the ethereal o x y g e n a t o m m i g h t a i d C — Ο — C bond

fission.

It is c o n c e i v a b l e that the d i o x i n s y i e l d i n i t i a l l y 2-phenoxy-


p h e n o l w h i c h c a n g i v e s y m m e t r i c a l h y d r o x y b i p h e n y l s b y ether fission,

rearrangement,

droxybenzenoid

and radical recombination.

compounds

might

be

formed

bond

Alternatively, dihy-

a n d w o u l d be

readily

susceptible to p h o t o o x i d a t i o n , y i e l d i n g p o l y m e r i c c o m p o u n d s . A l t h o u g h the effectiveness of s u n l i g h t i n d e s t r o y i n g T C D D i n d i l u t e m e t h a n o l s o l u t i o n was established c o n c l u s i v e l y , the i n s o l u b i l i t y of T C D D l i m i t e d studies i n aqueous systems.

P u r e c r y s t a l l i n e T C D D as a suspen

s i o n i n d i s t i l l e d w a t e r s e e m e d to b e u n c h a n g e d b y i r r a d i a t i o n w i t h s u n l a m p . H o w e v e r , i f a f e w drops of a s o l u t i o n of

1 4

a

C - T C D D i n benzene

w a s a d d e d to w a t e r a n d the d i s p e r s i o n was s t a b i l i z e d b y a

surfactant

s u c h as T w e e n - 8 0 , i r r a d i a t i o n w i t h a s u n l a m p w a s effective i n r e d u c i n g the T C D D content of the system.

B y contrast,

T C D D a p p l i e d to soil

or a s o l i d s u r f a c e s e e m e d to be extremely resistant to the a c t i o n of s u n l i g h t a n d d e c o m p o s e d v e r y s l o w l y . A spot of a m e t h a n o l i c s o l u t i o n of TCDD

(2.4

p p m ) was a p p l i e d to glass plates c o a t e d w i t h a u n i f o r m

250-/xm l a y e r of either N o r f o l k s a n d y s o i l or H a g e r s t o w n silty c l a y l o a m . T h e d r i e d spot w a s i l l u m i n a t e d for 96 hours w i t h a fluorescent u l t r a v i o l e t l a m p . A t the e n d of this p e r i o d T C D D c o u l d b e r e c o v e r e d q u a n t i t a t i v e l y unchanged.

T h e same results w e r e g i v e n b y d r y plates or b y

m o i s t e n e d w i t h w a t e r d u r i n g the experiment.

plates

Similarly, there was neg

l i g i b l e c h a n g e i n the q u a n t i t y of T C D D i r r a d i a t e d as a film o n a glass p l a t e f o r u p to 14 days (20).

It seems l i k e l y , therefore, that a n y loss of

T C D D f r o m a s o i l surface w o u l d o c c u r b y m e c h a n i c a l transfer o n dust particles rather t h a n b y v o l a t i l i z a t i o n or b y p h o t o d e g r a d a t i o n . Photochemical

Generation

of

Dioxins

L i g h t c a n effect the c o u p l i n g of p h e n o l s . M i l l e r (22)

F o r example, J o s c h e k a n d

f o u n d that p h e n o x y p h e n o l s c o u l d be p r o d u c e d i n the

flash

p h o t o l y s i s of p h e n o l , b u t a l t h o u g h sought, no d i o x i n was d e t e c t e d i n the reaction

products.

T h e i r r a d i a t i o n of aqueous solutions of 2 , 4 - d i c h l o r o p h e n o l a n d 2,4,5t r i c h l o r o p h e n o l w i t h U V l i g h t at w a v e l e n g t h s a b o v e 280 n m g a v e little


6.

P L I M M E R

reaction.

E T

A L .

51


H o w e v e r , i n t h e presence of r i b o f l a v i n as a sensitizer, t h e

p h e n o l s w e r e efficiently c o n s u m e d (23).

A d d e d o x y g e n seemed to i m

prove reaction yields, perhaps b y oxidizing reduced riboflavin. The

reaction products f r o m 2,4-dichlorophenol were

tetrachloro-

p h e n o x y p h e n o l s a n d t e t r a c h l o r o d i h y d r o x y b i p h e n y l s ( F i g u r e 5 ) , as d e t e r m i n e d f r o m t h e i r mass spectra

a n d those of t h e i r m e t h y l ethers.

4 , 6 - D i c h l o r o - 2 - ( 2 , 4 - d i c h l o r o p h e n o x y ) p h e n o l ( V ) w a s t h e major p h e n o x y /

phenol;

,

t h e mass s p e c t r a l f r a g m e n t a t i o n

pattern

of o - h y d r o x y p h e n o l

ethers is q u i t e characteristic since a h y d r o g e n transfer occurs d u r i n g t h e f r a g m e n t a t i o n ( F i g u r e 6 ) . A trace of a t r i c h l o r o p h e n o x y p h e n o l also w a s Downloaded by COLUMBIA UNIV on March 31, 2013 | http://pubs.acs.org Publication Date: March 1, 1973 | doi: 10.1021/ba-1973-0120.ch006

d e t e c t e d a n d w a s f o r m e d p r e s u m a b l y b y the u n s e n s i t i z e d r e d u c t i v e loss of c h l o r i n e , d i s c u s s e d p r e v i o u s l y . Two

i s o m e r i c t e t r a c h l o r o d i h y d r o x y b i p h e n y l s (m/e

3 2 2 ) also oc

curred i n the reaction mixture a n d were characterized b y the formation

CI Figure 5.

HO CI

Irradiation of 2,4-dichlorophenol + ·

CI

CI

CI

CI m/e 177

Figure 6.

Fragmentation of 4,6-dichloro-2-(2',4'-dichhrophenoxy)phenol


52

CHLORODIOXINS

of t h e i r d i m e t h y l ethers (m/e

350).

ORIGIN

AND

FATE

H o w e v e r , despite extensive destruc

t i o n of the p h e n o l s , t h e i r c o n v e r s i o n to d i m e r i c p r o d u c t s w a s less t h a n 5%.

A l t h o u g h measurements

w e r e c o n d u c t e d at several t i m e intervals,

at no t i m e c o u l d d i b e n z o - p - d i o x i n s b e detected i n the m i x t u r e of p r o d u c t s b y e l e c t r o n - c a p t u r e gas c h r o m a t o g r a p h y (20,

23).

OH

Cl> A^ci ClA^CI Jj

light ÔÏÏ®

>


CI

Figure 7.

Photolysis of pentachlorophenol

B y contrast, a l k a l i n e a q u e o u s solutions of 2 , 4 - d i c h l o r o p h e n o l , 2,4,5trichlorophenol, and pentachlorophenol rapidly colored w h e n

exposed

to s u n l i g h t . T h e i s o l a t i o n of several p h o t o l y s i s p r o d u c t s p r e d i c t a b l y de r i v e d b y h y d r o l y t i c a n d r e d u c t i v e reactions sorcinol f r o m pentachlorophenol)

(including

tetrachlorore-

suggested s t r o n g l y that a n u c l e o p h i l i c

i o n i c m e c h a n i s m is o p e r a t i v e ( F i g u r e 7 ). P u r e d i o x i n - f r e e P C P , i r r a d i a t e d as a 1000 p p m s o l u t i o n i n aqueous s o d i u m h y d r o x i d e w i t h l i g h t i n the 3 0 0 - 3 5 0 n m r e g i o n , gave a n e u t r a l b e n z e n e - s o l u b l e

extract w h i c h c o n

t a i n e d o c t a c h l o r o d i b e n z o - p - d i o x i n as s h o w n b y G L C / M S . y i e l d i n repeated

experiments

w a s not consistent

A l t h o u g h the

a n d the

maximum

c o n c e n t r a t i o n w a s o n l y 36 p p m i n a n y s i n g l e i r r a d i a t i o n , a s m a l l e r a m o u n t of a n u n i d e n t i f i e d n e u t r a l constituent also w a s present w h o s e r e t e n t i o n t i m e o n G L C c o r r e s p o n d e d to that of a h e p t a c h l o r o d i b e n z o - p - d i o x i n . Discussion It w o u l d b e d i f f i c u l t to estimate the q u a n t i t y of T C D D w h i c h enters the e n v i r o n m e n t e a c h year.

I n a d d i t i o n to the c o m m o n pesticides l i s t e d

i n T a b l e I, other c h l o r o p h e n o l s Tand t h e i r d e r i v a t i v e s are u s e d w i d e l y . F o r e x a m p l e , large a m o u n t s of the d i s i n f e c t a n t , h e x a c h l o r o p h e n e

(2,2 r

m e t h y l e n e b i s ( 3 , 4 , 6 - t r i c h l o r o p h e n o l ) ), are u s e d i n homes, hospitals, a n d i n d u s t r y , a n d the D o w c i d e s 2 a n d Β ( 2 , 4 , 5 - t r i c h l o r o p h e n o l a n d its s o d i u m s a l t ) are i n d u s t r i a l m i c r o b i o c i d e s . M o r e t h a n 50,000,000 lbs of t r i c h l o r o p h e n o l are m a d e i n the U n i t e d States e a c h y e a r (24), e v e n t u a l l y m u s t b e d i s p e r s e d i n the e n v i r o n m e n t . seems to b e v a r i a b l e b u t is g e n e r a l l y b e l o w 0.5 p p m

a n d m u c h of i t

The dioxin

content

(25).

Synthesis of T C D D i n s u n l i g h t c o u l d not b e e x p e c t e d to a d d a p p r e c i a b l y to this e n v i r o n m e n t a l b u r d e n .

T h e f o r m a t i o n rate f r o m c h l o r o

p h e n o l s is s t r o n g l y c o n c e n t r a t i o n - d e p e n d e n t ,

a n d its m e c h a n i s m r e q u i r e s


6.

P L I M M E R

E T

A L .

53


that t h e t w o c o l l i d i n g p h e n o l m o l e c u l e s b e i n a n i o n i c f o r m . T h e rate of t r i c h l o r o p h e n o l f o r m a t i o n f r o m d e r i v a t i v e s s u c h as 2,4,5-T is e x t r e m e l y s l o w , a n d its d i s p e r s a l i n the e n v i r o n m e n t w o u l d b e u n f a v o r a b l e t o p h e n o l f o r m a t i o n at levels r e q u i r e d f o r T C D D synthesis since 2,4,5-T is not c o n v e r t e d d i r e c t l y i n t o T C D D . I f w e c o n s i d e r t h e r a p i d rate at w h i c h the s i m p l e r d i o x i n s u n d e r g o p h o t o l y s i s , i t seems u n l i k e l y that 2,4,5-T a n d other c h l o r o p h e n o l - b a s e d p e s t i c i d e s — o r

2,4-D,

even the phenols

themselves—normally w i l l f o r m the dioxins i n the environment. P C P presents a different p i c t u r e f r o m that of the l o w e r c h l o r o p h e n o l s


and their derivatives.

T h e c o r r e s p o n d i n g d i o x i n shows m u c h m o r e sta

b i l i t y to l i g h t t h a n does T C D D , e n o u g h to p e r m i t its p r o l o n g e d existence at l o w concentrations

i n a photoreactor.

A s a phenol it can directly

y i e l d d i o x i n s , a process f a v o r e d b y its n o r m a l m o d e of a p p l i c a t i o n as t h e s o d i u m salt. A l t h o u g h o c t a c h l o r o d i b e n z o - p - d i o x i n has m u c h l o w e r m a m malian toxicity than T C D D

( 6 ) , its f o r m a t i o n , properties, a n d effects

d e m a n d a d d i t i o n a l i n v e s t i g a t i o n . T e c h n i c a l p r e p a r a t i o n s of P C P are fre q u e n t l y mixtures of tetra- a n d p e n t a c h l o r o p h e n o l s ; c o n s e q u e n t l y ,

hepta-

a n d p o s s i b l y h e x a c h l o r o d i b e n z o - p - d i o x i n s m i g h t b e expected as p h o t o l y s i s products i n addition to the octachloro derivative. T C D D d e t e c t i o n has n o t b e e n r e p o r t e d i n the

field.

P e r h a p s , this

s h o u l d not b e s u r p r i s i n g , c o n s i d e r i n g t h e serious d i f f i c u l t y of its analysis, its p h o t o l y t i c b r e a k d o w n , a n d the f a c t that a n o r m a l a p p l i c a t i o n ( 2 l b s / a c r e ) of 2,4,5-T, f o r e x a m p l e , u s u a l l y w o u l d represent the d i s p e r s a l of n o m o r e t h a n 450 μg of the d i o x i n o n each treated acre, a s s u m i n g a d i o x i n content of < 0 . 5 p p m . L i k e w i s e , there seem t o b e n o reports of t h e d e c a y of h i g h l y d i s p e r s e d d i o x i n s o n leaf surfaces, a n d it m u s t b e r e c o g n i z e d that t h e experiments w e h a v e r e p o r t e d here w e r e c o n d u c t e d o n l y u n d e r the a r t i f i c i a l c o n d i t i o n s of the l a b o r a t o r y .

Nevertheless, the p h o t o c h e m

istry of t h e d i o x i n s s h o u l d p r o v i d e a w o r t h w h i l e r e m i n d e r that s u n l i g h t c a n act o n m a n - m a d e c h e m i c a l s i n the e n v i r o n m e n t t o f o r m p r o d u c t s w h i c h m a y b e m o r e toxic t h a n t h e o r i g i n a l to some l i f e f o r m a n d that a c o m p o u n d s h o w n to b e h i g h l y t o x i c u n d e r r i g i d l y s t a n d a r d i z e d c o n d i t i o n s does n o t necessarily present the same h a z a r d w h e n the toxicant is exposed to t h e forces of nature.

Literature

Cited

1. California Department of Agriculture, "Pesticide Use Report 1970," Sacra mento, California, 1971. 2. Kimura, H . S., Hurov, H. R., "Evaluation of Pesticide Problems in Hawaii," Appendix, p. 25, Hawaii Department of Agriculture, Honolulu, 1969. 3. Whiteside, T., "Defoliation," p. 129, Ballantine, New York, 1970. 4. Kimmig, J., Schulz, Κ. H . , Dermatologica (1957) 195, 540. 5. Bauer, H . , Schulz, Κ. H., Arch. Pathol. Gewerbehyg. (1961) 583.



54

CHLORODIOXINS

ORIGIN

A N D FATE

6. Panel on Herbicides, President's Science Advisory Committee, "Report on 2,4,5-T," Executive Office of the President, Washington, D . C . (1971). 7. Emerson, J. L., Thompson, D . J., Strebing, R. J., Gerbig, C. G., Robinson, V. B., Fd. Cosmet. Toxicol. (1971) 9, 395. 8. Higginbotham, G. R., Huang, Α., Firestone, D., Verrett, J., Ress, J., Camp bell, A. D., Nature (1968) 220, 702. 9. Crosby, D. G . , Tutass, H . O., J. Agr. Food Chem. (1966) 14, 596. 10. Crosby, D. G . , Wong, A. S., 161st Nat. Meet. Amer. Chem. Soc., Los Angeles (April 1971). 11. Crosby, D . G . , Hamadmad, N., J. Agr. Food Chem. (1971) 19, 1171. 12. Kuwahara, M . , Kato, N . , Munakata, K., Agr. Biol. Chem. (Tokyo) (1966) 30, 232, 239. 13. Plimmer, J. R., Residue Rev. (1971) 33, 47. 14. Plimmer, J. R., Hummer, Β. E., 155th Nat. Meet. Amer. Chem. Soc., San Francisco (April 1968). 15. Crosby, D . G . , Leitis, E . , J. Agr. Food Chem. (1969) 17, 1033. 16. Pinhey, J. T., Rigby, R. D. G . , Tetrahedron Lett. 1970, 1267. 17. Wolf, W., Kharasch, N . , J. Org. Chem. (1965) 30, 2493. 18. Kearney, P. C., Woolson, Ε . Α., Plimmer, J. R., Isensee, A. R., Residue Rev. (1969) 29, 137. 19. Crosby, D . G . , Residue Rev. (1969) 25, 1. 20. Crosby, D. G., Wong, A. S., Plimmer, J. R., Woolson, Ε. Α., Science (1971) 173, 748. 21. Ogata, Y., Tagaki, K., Ishino, I., Tetrahedron (1970) 26, 2703. 22. Joschek, Η. I., Miller, S. I., J. Amer. Chem. Soc. (1971) 88, 407. 23. Plimmer, J. R., Klingebiel, U . I., Science (1971) 174, 407. 24. United States Tariff Commission, "Synthetic Organic Chemicals," p. 52, T C Publication 295, Washington, D . C., 1969. 25. Woolson, Ε . Α., Thomas, R. F . , Ensor, P. D . J., J. Agr. Food Chem. (1972) 20, 351. R E C E I V E D February 23,

1972.


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