- Email: [email protected]
Photochemical quantum yields and sunlight half-lives of polychlorodibenzo-p -dioxins in aquatic systems
C h e m o s p h e r e , Vol.15, N o s . 9 - 1 2 , P r i n t e d in G r e a t B r i t a i n
pp 1935-1940,
1986
0 0 4 5 - 6 5 3 5 / 8 6 $ 3 . 0 0 + .OO P e r g a m o n J o u r n a l s Ltd.
PHOTOCH~ICAL QUANTUM YIELDS AND SUNLIGHT HALF-LIVES OF POLYCHLORODIBENZO-~-DIOXINS IN AQUATIC SYST~S
Ghulam Ghaus Choudhry ~ and G.R. Barrie Webster Pesticide Research Laboratory, Department of Soil Science University of Manitoba, Winnipeg, Manitoba, Canada
R3T 2N2
ABSTRACT The quantum yields (~tr x) for the direct phototrasformation of 1,2,3,7tetrachlorodibenzo-~-dioxin'~l,2,3,7-T4CDD ) (1) an~ 1,3,6,8-T4CDD (2) in H20-~H3CN (2:3 v/v) measured at 313 nm were (5.424 ± 0.422) ~ i0-~ and (2.170 ± 0.T35) x I0 -J, respectively. The values of ~tr ~ for dioxins I and 2 as well as those of 1,2,3,4,7-P~CDD (3), 1,2,3,4,7,8-H6CDD (4), I,~,~4,6,7,8-H7CDD-(5 ) a~d 08CDD (6) (previously reported~ w~re utilized for the estimation of the sunlight ~hotolysis hal~-lives ((ti)s~) of these pollutants. For example, during summer, (t~)o~ of the PCDDs i-6 are expected ~o be 1.77 ± 0.14, 0.31 ± 0.02, 15.16 ± 3.67, 6.27 ± 0. iI,=~7.33 ± 5.11, a~d--17.85 ± 2.62 days, respectively. INTRODUCTION Concern has grown regarding environmental contamination by polychlorinated dibenzo-~dioxins (PCDDs) 1'2.
Photochemical degradation may be an important process affecting
atmospheric contaminants and chemicals that reside on surfaces (pesticides on leaves and vegetation) or in water bodies.
Recently, we have cirtically reviewed existing photolytic
test methods and have further proposed protocol guidelines applicable for the investigations of photochemical fate of pesticides (and other chemicals) occurring in water, air and soils for Environment Canada, Ottawa 3. Although a good deal of research on the photolytic fate of PCDDs, both in solution and solid phase has appeared 4, to the best of our knowledge, no investigator has reported the quantum yields (~) for the photolysis of these environmental pollutants.
However, we have
recently reported the kinetics and quantum yields for the direct phototransformation (~tr,l) of solutions of four isomers of penta- through octachlorodibenzo-~-dioxins in water acetonitrile (2:3 v/v) at wavelength (I) = 313 nm 5'6 determined using the above described guidelines 3 .
1935
1936
In view of our continuing interest in the photochemical fate of chlorinated aromatic pollutants (CAPs) present in the environment, we have further investigated the environmental solution phase photochemistry of l, 2,3,7-tetrachlorodibenzo-l-dioxin (f,2,3,7-T4CDD)
(i) and 1,3,6,8-T4CDD (2) in aqueous acetonitrile.
This paper presents
data concerning the Ctr,l at 313 nm along with the sunlight half-lives of CAPs 1 and 2. El
O
Ci 1
2 EXPERIMENTAL
S o u r c e s of t h e PCDDs 1 and 2 as w e l l as s o l v e n t s were t h e same as p r e v i o u s l y r e p o r t e d 5.
Solutions
of T4CDDs 1 and i
p r o c e d u r e s of t h e p r e p a r a t i o n
i n H20-CH3CN ( 2 : 3 v / v ) were p r e p a r e d f o l l o w i n g t h e
of s i m i l a r
solution
of 1,2,3,4,7,8-H6CDD
(4) .5 ( s e e b e l o w ) .
Photolyses of the substrates were conducted on the Rayonet Photochemical Reactor having an energy output of 90% between 290 and 310 nm equipped with a merry-go-round apparatus, described elsewhere 7'8. filter solution,
The Pyrex photoreaction cells with I cm-pathlength (£), chemical
and chemical actinometer (for the determination of the intensity (Ik) of
the filtered incident light from the Rayonet RPR 3000 ~ lamps) have been cited in the previous articles 3'5.
The analyses of the sample solutions of the T4CDD 1 and 2 were
performed by RP-HPLC 5 using methanol as eluant; and a flow rate of 1.O mL/min.
Forty
microlitres oi ],2,3,4,6,7,8-H7CDD (5) (7.255 x 10-5 M) in CH3CN were added to each sample (2 mL) solution of the candidate dioxin as an internal standard prior to analysis. Procedures for the analysis of the actinometer solution were the same as described elsewhere ~.
RESULTS AND DISCUSSION l.O
Figures i and 2 show typical
!
j
r ° 0.99350
first-order plots (eq.1):
I
in (Po/Pt) = kp,~t
0.8 t slope - 7. 193x10-2 h-1
(I)
of the photolysis data for //'/ /"
0"6 i
dilute solutions (absorbance being < 0.02 at 313 nm) of two individual congeners of PCDDs,
I
o =
,fm
0.4 !
namely 1,2,3,7nT4CDD (!)
./
(6.400 ~M) and 1,3,6,8-T4CDD (2) (10.554 ~M) in H20-CH3CN
/./" 0.2 t
(2:3 v/v).
,/ .a
In eq. (i) Po and
Pt are the concentrations of a PCDD isomer at times
r
0.0 i-" 0.0
-/% ,
zero and t, respectively; , 2.0
,
[ 4 0
I. 6 0
'
I
8.0
I
-I0.0
whereas kp,% is the phototransformation first-order rate
IrradistLon
Figure I.
tlme (h)
First-order treatment of the photolysis data for 1,2,3,7-T4CDD (I) in water-acetonitrile (2:3 v/v).
constant of the CAP at % = 313 nm.
1937
1.0 r -
/ /
0.99423
s l o p e - 2 . 1 2 8 x 1 0 -1 h -1
/
Standard linear regression (Energraphics) was utilized for
//.
0.8
/I /
/
the plots depicted by Figures I
/
and 2.
/" /
0.6
kp, x ( h - l ) .
•/t // /" c. v
0.4 /
/
/i
photolytic data for CAPs ! and
/ I/
2 was done.
•
Average values of the kp,~
/'* /
o. 2
./t
Similar
treatment of the additional
/
c.
The slopes of these
plots provided the values of
./
(sec -I) for T4CDDs ! and i,
,/P"
determined in the above mentioned manner, are recorded
o.o
/
/
i
0.0
i
F
Table I. I
I
2,0
1.0
t
I
I 6.0
3.0
In order to determine
I
5.0
the quantum yield (~tr,~) for the direct phototransformation
I r r a d i a t i o n Time (h)
of dioxins i and 2 at % = 313 Figure 2.
First-order treatment of the photolysis data for 1,3,6,8-T4CDD (2) in water-acetonitrile (2:3 v/v).
nm, data for molar extinction coefficient (e%) (2714 and 2255
L.Mol-l.cm -I, respectively) in CH3CN, kp,% (Table i) and l~(measured with the aid of simultaneous photolysis of the actinometer solution 5) together with the following relationship (eq. (2)) were used3'5'9-11: @tr,% =
k P~l 2.303 l%c%E
where ~ was 1.00 cm. in this manner.
(2)
Table I includes the values of ~tr,~
for CAPs ! and ~, determined
In Table I, previously reported data on kp ~. and ~tr,~ for 1,2,3,4,7-
P5CD D (~)5, 1,2,3,4,7,8_H6CD D (~)5, 1,2,3,4,6,7,8_H7CD D (!)~, and 1,2,3,4,6,7,8,9-08CDD CI
Ca
Ct
CI
Co
Ct" ~ f " "0 c0
CL
c
C~'v'O"
~
0
"Cu Ct
3
O" ~ c~
4
"0" " r / " 0 ci
5
0
6
(6) 6 are also documented for comparison. Table II records estimated direct sunlight photolysis half-lives ((t½)sp) of CAPs !-6 present in water-bodies at latitude 40 ° N during different seasons. for dioxins !-~ were calculated using data On~r,E (Table I), (Z)
~,
The values of (t½)sp and solar intensity
(available in the literature 3,11) along with the previously described
relationships 3,5,9.
For instance, in summer (t½)sp of dioxins 1_-6 would be 1.77 ± O.14,
0.31 ± 0.02, 15.16 ± 3.67, 6.27 i 0. II, 47.33 ± 5.11, and 17.85 ± 2.62 days, respectively. Detailed discussions of the environmental photochemistry of the investigated PCDDs will be presented elsewhere 12. ACKNOWLEDGEMENT We appreciate and acknowledge the financial support for this project by the National Wildlife Research Centre, Canadian Wildlife Service, Ottawa, Ontario, Canada.
1,2,3,4,7-P5CDDC
1,2,3,4,7,8-H6CDDC
1,2,~,4,6,7,8-H7CDDd
O8CDD
(3)
(4)
(5)
(6)
dData from previous work 6.
CData from previous work 5.
bData from present work.
aEq. (2) was used.
1,2,3,7-T4CDDb
1,3,6,8-T4CDD b
(I)
(2)
Substrate
No.
time,
ing dioxin,
0.31
2.78
3.33
2.81
10.55
6.40
(lO-6M)
112
72
72
72
4
8
tmax (h)
irradiation
of the start-
Po
of the
Maximum
concentration
(%)
52.9
39.1
87.2
71.2
57.1
39.5
tmax
dioxin after
starting
disappearance
percentage
Average
Photolysis of PCDDs in Water-Acetonitrile
Initial
Table I.
1.O6±0.14
1.O2±O.II
7.86±0.03
4.31±0.70
59.57±2.81
18.13±1.40
kP,X , (I0 -0 sec -~ )
order rate constant,
Photolysis first-
(2:3 v/v) at 313 nm.
(2.26±0.31)xi0 -5
(1.53~0.17)xI0 -5
(l.10±O.O2)xlO -4
(9.78±2.38)xi0 -5
(2.17±0.14)xi0 -3
(5.42±0.42)xi0 -4
~tr,X
transformation
the direct photo-
Quantum yield a for
Oo
%O
8.73±0.68
1,47±0.09
CRequired data from previous work was used 6.
aData from present work. bData from previous work 5.
over full year
Averaged
0.53±0.03
3.20±0.25
5.42±0.42
Fall
Winter
0.84±0.05
0.31±0.02
1.77±0.14
0.35±0.02
2.08_+0.16
Spring
(t½)sp (days)
(t½)sp (days)
Summer
Seasons
1,3,6,8TaCDD(~) a
1,2,3,7-
76.82±18.69
52.37±12.85
28.59±6.91
15.16±3.67
18.29±4.44
(t½)sp (days)
P5CDD(~)b
1,2,3,4,7-
31.85±0.63
21.57±0.41
11.87±0.21
6.27±0.11
7.57±0.14
(t½)sp (days)
H6CDD(~)b
1,2,3,4,7,8-
Aquatic Bodies for Latitude 40°N for Various Seasons.
2392.68±281.50
[55.79±16.75
87.86±9.51
47.33±5.11
56.46±6.13
(t½)sp (days)
HFCDD(!) c
1,2,3,4,6,7,8-
Calculated Direct Sunlight Photolysis Half-Lives ((t~)sp) of PCDDs in
T4CDD(!) a
Table II.
863.22±127.21
50.45±7.39
31.26±4.59
17.85±2.62
20.55±3.01
(t½)sp (days)
08CDD(6)c
~0 kO
~D
1940
REFERENCES (15
G.G. Choudhry and O. Hutzinger, "Mechanistic Aspects of the Thermal Formation of Halogenated Organic Compounds Including Polychlorinated Dibenzo-l-dioxins", Gordon and Breach Sci. Publ., New York, (1983).
(2)
M.J. Boddington, P. Barrette, D. Grant, R.J. Norstrom, J.J. Ryan and L. Whitley, Guest Editors, Proceedings of the Fourth International Symposium on "Chlorinated Dioxins and Related Compounds", Ottawa, Canada, Oct. 16-18, 1984, Chemosphere pp.575-989 (1985).
(3)
G.G. Choudhry and 6.R.B. Webster, Residue Rev. 96, 79 (1985); in press.
(4)
G.G. Choudhry and O. Hutzinger, Residue Rev. 84, 113 (1982).
(5)
G.G. Choudhry and G.R.B. Webster, Chemosphere 14, 9 (1985).
(6)
G.G. Choudhry and G.R.B. Webster, Chemosphere 14, 893 (1985).
(7)
G.G. Choudhry , A.A.M. Roof, and O. Hutzinger, J. Chem. Soc. Perkin Trans. i, 2957
(8)
(1982). G.G. Choudhry , J.A. van den Broecke, and O. Hutzinger, Chemosphere 12, 487 (1983).
(9)
G.G. Choudhry, "Humic Substances:
Structural, Photophysical, Photochemical and
Free Radical Aspects and Interactions with Environmental Chemicals", Gordon and Breach Sci. Publ., New York, pp.158, 159 (1984). (i0)
T. Mill, W.R. Mabey, B.Y. Lan and A. Baraze, Chemosphere i0, 1281 (1981).
(ii)
R.G. Zepp, "Experimental Approaches to Environmental Photochemistry", The Handbook of Environmental Chemistry, ed. O. Hutzinger, Vol. 2 Part B, Springer-Verlag, Berlin, West Germany, pp.19-41 (1982).
(12)
G.G. Choudhry and G.R.B. Webster, manuscript in preparation, 1986.
pp 1935-1940,
1986
0 0 4 5 - 6 5 3 5 / 8 6 $ 3 . 0 0 + .OO P e r g a m o n J o u r n a l s Ltd.
PHOTOCH~ICAL QUANTUM YIELDS AND SUNLIGHT HALF-LIVES OF POLYCHLORODIBENZO-~-DIOXINS IN AQUATIC SYST~S
Ghulam Ghaus Choudhry ~ and G.R. Barrie Webster Pesticide Research Laboratory, Department of Soil Science University of Manitoba, Winnipeg, Manitoba, Canada
R3T 2N2
ABSTRACT The quantum yields (~tr x) for the direct phototrasformation of 1,2,3,7tetrachlorodibenzo-~-dioxin'~l,2,3,7-T4CDD ) (1) an~ 1,3,6,8-T4CDD (2) in H20-~H3CN (2:3 v/v) measured at 313 nm were (5.424 ± 0.422) ~ i0-~ and (2.170 ± 0.T35) x I0 -J, respectively. The values of ~tr ~ for dioxins I and 2 as well as those of 1,2,3,4,7-P~CDD (3), 1,2,3,4,7,8-H6CDD (4), I,~,~4,6,7,8-H7CDD-(5 ) a~d 08CDD (6) (previously reported~ w~re utilized for the estimation of the sunlight ~hotolysis hal~-lives ((ti)s~) of these pollutants. For example, during summer, (t~)o~ of the PCDDs i-6 are expected ~o be 1.77 ± 0.14, 0.31 ± 0.02, 15.16 ± 3.67, 6.27 ± 0. iI,=~7.33 ± 5.11, a~d--17.85 ± 2.62 days, respectively. INTRODUCTION Concern has grown regarding environmental contamination by polychlorinated dibenzo-~dioxins (PCDDs) 1'2.
Photochemical degradation may be an important process affecting
atmospheric contaminants and chemicals that reside on surfaces (pesticides on leaves and vegetation) or in water bodies.
Recently, we have cirtically reviewed existing photolytic
test methods and have further proposed protocol guidelines applicable for the investigations of photochemical fate of pesticides (and other chemicals) occurring in water, air and soils for Environment Canada, Ottawa 3. Although a good deal of research on the photolytic fate of PCDDs, both in solution and solid phase has appeared 4, to the best of our knowledge, no investigator has reported the quantum yields (~) for the photolysis of these environmental pollutants.
However, we have
recently reported the kinetics and quantum yields for the direct phototransformation (~tr,l) of solutions of four isomers of penta- through octachlorodibenzo-~-dioxins in water acetonitrile (2:3 v/v) at wavelength (I) = 313 nm 5'6 determined using the above described guidelines 3 .
1935
1936
In view of our continuing interest in the photochemical fate of chlorinated aromatic pollutants (CAPs) present in the environment, we have further investigated the environmental solution phase photochemistry of l, 2,3,7-tetrachlorodibenzo-l-dioxin (f,2,3,7-T4CDD)
(i) and 1,3,6,8-T4CDD (2) in aqueous acetonitrile.
This paper presents
data concerning the Ctr,l at 313 nm along with the sunlight half-lives of CAPs 1 and 2. El
O
Ci 1
2 EXPERIMENTAL
S o u r c e s of t h e PCDDs 1 and 2 as w e l l as s o l v e n t s were t h e same as p r e v i o u s l y r e p o r t e d 5.
Solutions
of T4CDDs 1 and i
p r o c e d u r e s of t h e p r e p a r a t i o n
i n H20-CH3CN ( 2 : 3 v / v ) were p r e p a r e d f o l l o w i n g t h e
of s i m i l a r
solution
of 1,2,3,4,7,8-H6CDD
(4) .5 ( s e e b e l o w ) .
Photolyses of the substrates were conducted on the Rayonet Photochemical Reactor having an energy output of 90% between 290 and 310 nm equipped with a merry-go-round apparatus, described elsewhere 7'8. filter solution,
The Pyrex photoreaction cells with I cm-pathlength (£), chemical
and chemical actinometer (for the determination of the intensity (Ik) of
the filtered incident light from the Rayonet RPR 3000 ~ lamps) have been cited in the previous articles 3'5.
The analyses of the sample solutions of the T4CDD 1 and 2 were
performed by RP-HPLC 5 using methanol as eluant; and a flow rate of 1.O mL/min.
Forty
microlitres oi ],2,3,4,6,7,8-H7CDD (5) (7.255 x 10-5 M) in CH3CN were added to each sample (2 mL) solution of the candidate dioxin as an internal standard prior to analysis. Procedures for the analysis of the actinometer solution were the same as described elsewhere ~.
RESULTS AND DISCUSSION l.O
Figures i and 2 show typical
!
j
r ° 0.99350
first-order plots (eq.1):
I
in (Po/Pt) = kp,~t
0.8 t slope - 7. 193x10-2 h-1
(I)
of the photolysis data for //'/ /"
0"6 i
dilute solutions (absorbance being < 0.02 at 313 nm) of two individual congeners of PCDDs,
I
o =
,fm
0.4 !
namely 1,2,3,7nT4CDD (!)
./
(6.400 ~M) and 1,3,6,8-T4CDD (2) (10.554 ~M) in H20-CH3CN
/./" 0.2 t
(2:3 v/v).
,/ .a
In eq. (i) Po and
Pt are the concentrations of a PCDD isomer at times
r
0.0 i-" 0.0
-/% ,
zero and t, respectively; , 2.0
,
[ 4 0
I. 6 0
'
I
8.0
I
-I0.0
whereas kp,% is the phototransformation first-order rate
IrradistLon
Figure I.
tlme (h)
First-order treatment of the photolysis data for 1,2,3,7-T4CDD (I) in water-acetonitrile (2:3 v/v).
constant of the CAP at % = 313 nm.
1937
1.0 r -
/ /
0.99423
s l o p e - 2 . 1 2 8 x 1 0 -1 h -1
/
Standard linear regression (Energraphics) was utilized for
//.
0.8
/I /
/
the plots depicted by Figures I
/
and 2.
/" /
0.6
kp, x ( h - l ) .
•/t // /" c. v
0.4 /
/
/i
photolytic data for CAPs ! and
/ I/
2 was done.
•
Average values of the kp,~
/'* /
o. 2
./t
Similar
treatment of the additional
/
c.
The slopes of these
plots provided the values of
./
(sec -I) for T4CDDs ! and i,
,/P"
determined in the above mentioned manner, are recorded
o.o
/
/
i
0.0
i
F
Table I. I
I
2,0
1.0
t
I
I 6.0
3.0
In order to determine
I
5.0
the quantum yield (~tr,~) for the direct phototransformation
I r r a d i a t i o n Time (h)
of dioxins i and 2 at % = 313 Figure 2.
First-order treatment of the photolysis data for 1,3,6,8-T4CDD (2) in water-acetonitrile (2:3 v/v).
nm, data for molar extinction coefficient (e%) (2714 and 2255
L.Mol-l.cm -I, respectively) in CH3CN, kp,% (Table i) and l~(measured with the aid of simultaneous photolysis of the actinometer solution 5) together with the following relationship (eq. (2)) were used3'5'9-11: @tr,% =
k P~l 2.303 l%c%E
where ~ was 1.00 cm. in this manner.
(2)
Table I includes the values of ~tr,~
for CAPs ! and ~, determined
In Table I, previously reported data on kp ~. and ~tr,~ for 1,2,3,4,7-
P5CD D (~)5, 1,2,3,4,7,8_H6CD D (~)5, 1,2,3,4,6,7,8_H7CD D (!)~, and 1,2,3,4,6,7,8,9-08CDD CI
Ca
Ct
CI
Co
Ct" ~ f " "0 c0
CL
c
C~'v'O"
~
0
"Cu Ct
3
O" ~ c~
4
"0" " r / " 0 ci
5
0
6
(6) 6 are also documented for comparison. Table II records estimated direct sunlight photolysis half-lives ((t½)sp) of CAPs !-6 present in water-bodies at latitude 40 ° N during different seasons. for dioxins !-~ were calculated using data On~r,E (Table I), (Z)
~,
The values of (t½)sp and solar intensity
(available in the literature 3,11) along with the previously described
relationships 3,5,9.
For instance, in summer (t½)sp of dioxins 1_-6 would be 1.77 ± O.14,
0.31 ± 0.02, 15.16 ± 3.67, 6.27 i 0. II, 47.33 ± 5.11, and 17.85 ± 2.62 days, respectively. Detailed discussions of the environmental photochemistry of the investigated PCDDs will be presented elsewhere 12. ACKNOWLEDGEMENT We appreciate and acknowledge the financial support for this project by the National Wildlife Research Centre, Canadian Wildlife Service, Ottawa, Ontario, Canada.
1,2,3,4,7-P5CDDC
1,2,3,4,7,8-H6CDDC
1,2,~,4,6,7,8-H7CDDd
O8CDD
(3)
(4)
(5)
(6)
dData from previous work 6.
CData from previous work 5.
bData from present work.
aEq. (2) was used.
1,2,3,7-T4CDDb
1,3,6,8-T4CDD b
(I)
(2)
Substrate
No.
time,
ing dioxin,
0.31
2.78
3.33
2.81
10.55
6.40
(lO-6M)
112
72
72
72
4
8
tmax (h)
irradiation
of the start-
Po
of the
Maximum
concentration
(%)
52.9
39.1
87.2
71.2
57.1
39.5
tmax
dioxin after
starting
disappearance
percentage
Average
Photolysis of PCDDs in Water-Acetonitrile
Initial
Table I.
1.O6±0.14
1.O2±O.II
7.86±0.03
4.31±0.70
59.57±2.81
18.13±1.40
kP,X , (I0 -0 sec -~ )
order rate constant,
Photolysis first-
(2:3 v/v) at 313 nm.
(2.26±0.31)xi0 -5
(1.53~0.17)xI0 -5
(l.10±O.O2)xlO -4
(9.78±2.38)xi0 -5
(2.17±0.14)xi0 -3
(5.42±0.42)xi0 -4
~tr,X
transformation
the direct photo-
Quantum yield a for
Oo
%O
8.73±0.68
1,47±0.09
CRequired data from previous work was used 6.
aData from present work. bData from previous work 5.
over full year
Averaged
0.53±0.03
3.20±0.25
5.42±0.42
Fall
Winter
0.84±0.05
0.31±0.02
1.77±0.14
0.35±0.02
2.08_+0.16
Spring
(t½)sp (days)
(t½)sp (days)
Summer
Seasons
1,3,6,8TaCDD(~) a
1,2,3,7-
76.82±18.69
52.37±12.85
28.59±6.91
15.16±3.67
18.29±4.44
(t½)sp (days)
P5CDD(~)b
1,2,3,4,7-
31.85±0.63
21.57±0.41
11.87±0.21
6.27±0.11
7.57±0.14
(t½)sp (days)
H6CDD(~)b
1,2,3,4,7,8-
Aquatic Bodies for Latitude 40°N for Various Seasons.
2392.68±281.50
[55.79±16.75
87.86±9.51
47.33±5.11
56.46±6.13
(t½)sp (days)
HFCDD(!) c
1,2,3,4,6,7,8-
Calculated Direct Sunlight Photolysis Half-Lives ((t~)sp) of PCDDs in
T4CDD(!) a
Table II.
863.22±127.21
50.45±7.39
31.26±4.59
17.85±2.62
20.55±3.01
(t½)sp (days)
08CDD(6)c
~0 kO
~D
1940
REFERENCES (15
G.G. Choudhry and O. Hutzinger, "Mechanistic Aspects of the Thermal Formation of Halogenated Organic Compounds Including Polychlorinated Dibenzo-l-dioxins", Gordon and Breach Sci. Publ., New York, (1983).
(2)
M.J. Boddington, P. Barrette, D. Grant, R.J. Norstrom, J.J. Ryan and L. Whitley, Guest Editors, Proceedings of the Fourth International Symposium on "Chlorinated Dioxins and Related Compounds", Ottawa, Canada, Oct. 16-18, 1984, Chemosphere pp.575-989 (1985).
(3)
G.G. Choudhry and 6.R.B. Webster, Residue Rev. 96, 79 (1985); in press.
(4)
G.G. Choudhry and O. Hutzinger, Residue Rev. 84, 113 (1982).
(5)
G.G. Choudhry and G.R.B. Webster, Chemosphere 14, 9 (1985).
(6)
G.G. Choudhry and G.R.B. Webster, Chemosphere 14, 893 (1985).
(7)
G.G. Choudhry , A.A.M. Roof, and O. Hutzinger, J. Chem. Soc. Perkin Trans. i, 2957
(8)
(1982). G.G. Choudhry , J.A. van den Broecke, and O. Hutzinger, Chemosphere 12, 487 (1983).
(9)
G.G. Choudhry, "Humic Substances:
Structural, Photophysical, Photochemical and
Free Radical Aspects and Interactions with Environmental Chemicals", Gordon and Breach Sci. Publ., New York, pp.158, 159 (1984). (i0)
T. Mill, W.R. Mabey, B.Y. Lan and A. Baraze, Chemosphere i0, 1281 (1981).
(ii)
R.G. Zepp, "Experimental Approaches to Environmental Photochemistry", The Handbook of Environmental Chemistry, ed. O. Hutzinger, Vol. 2 Part B, Springer-Verlag, Berlin, West Germany, pp.19-41 (1982).
(12)
G.G. Choudhry and G.R.B. Webster, manuscript in preparation, 1986.