Bull. Environ. Contam. Toxicol. (1992) 49:368-374 9 1992 Springer-Verlag New York Inc.
~l=nvironrnenll;al ~Contarnirmll;ion l a n d "lllaxicxalo~]
Photochemical Behavior of Organic Phosphate Esters in Aqueous Solutions Irradiated with a Mercury Lamp Seiichi Ishikawa, 1 Yutaka Uchimura, 2 Kenzo Baba, 2 Yoshio Eguchi, 1 and Kozo Kido ~ ~Kitakyushu Municipal Institute of Environmental Health Sciences, Shinike 1-2-1, Tobata Kitakyushu Fukuoka, 804, Japan and 2Water Quality Control Division, Kitakyushu Municipal Sewerage Bureau, Nish minato 96-3, Kokurak ta, Kitakyushu, Fukuoka, 804, Japan Pollution by t o x i c chemicals that are resistant to biological degradation and h a v e a p o t e n t i a l for accumulation in biological organisms is becoming a world-wide problem. Organic phosphate esters(OPEs) are widely used as plasticizers, industrial hydraulic fluids, an d l u b r i c a n t additives. Various OPEs h a v e b e e n d e t e c t e d in environmental samples (Tachikama et 1977; Ishikama et al. mastewaters (Ishikawa
al. 1975; Office of Health Studies 1985c) and in industrial and d o m e s t i c et al. 1985a).
Ultraviolet(UV) irradiation i s known as a e f f e c t i v e treatment for persistent chemicals in natural water wastewater ( C r o s b y a n d Hamadmad 1 9 7 1 ; T i s s o t et al.
or 1984).
Therefore, in order to develop a means o f r e m o v a l o f 0PEs i n mater, some f u n d a m e n t a l experiments w i t h OV i r r a d i a t i o n were performed w i t h a m e r c u r y l a m p , and p h o t o c h e m i c a l behaviors an d p h o t o d e c o m p o s i t i o n products were examined for 7 0PEs, namely tributyl phosphate(TBP), tris(chloropropyl) phosphate (TCPP), tris(2-chloroethyl) phosphate(TCEP), trioctyl phosphate(TOP), tris(dichloropropyl) phosphate(CRP), triphenyl
phosphate(TPP),
MATERIALS
AND METHODS
and
tricresyl
phosphate(TCP).
The r e a c t o r used in these experiments was a T a i k a K o g y o M o d e l HLV-A e q u i p p e d w i t h a 15 W l o w - p r e s s u r e mercury lamp. The g a s c h r o m a t o g r a p h ( t i C ) was a N i h o n D e n s h i M o d e l JfiC-2OK equipped with a flame ionization detector and a flame photometric detector having a 526-nm filter. Th e tic conditions were as follows: 2 mm i . d . x 2 m glass column p a c k e d w i t h 2~ 0 V - 1 7 § 2~ P Z - 1 7 9 c o a t e d on 6 0 - 8 0 m e s h
Send
reprint
request
to
S.
Ishikawa.
368
Uniport HPS; inlet temperature, 300 "C; column temperature, 100-300 "C and 200-300 "C(10 "C/min); c a r r i e r gas, 20 mL/min of n i t r o g e n gas; d e t e c t o r temperature, 300 "C. GC-mass spectrometer(GC-HS) was a N i h o n Denshi Hodel J H S - D X 303. The o p e r a t i o n a l c o n d i t i o n s had the same column and column t e m p e r a t u r e was p r o g r a m m e d from 100 to 280 "C at I0 "C/min. Inlet temperature was 2 9 0 " C . T h e h e l i u m f l o w r a t e w a s 10 mL/min. Ionizing e n e r g y mas 70 eV. Total organic carbon (TOC) a n d i n o r g a n i c carbon(IC) were measured with a Beckman H o d e l 915A TOC a n a l y z e r . Seven OPEs mere o b t a i n e d from Tokyo Chemical Co. TBP, TCEP, TOP, and TCP were p u r i f i e d by d i s t i l l a t i o n under reduced pressure. TCPP and CRP mere used without further purification. TPP was p u r i f i e d by zone refining. The purity of these OPEs was checked by GC. TCPP, CRP, and TCP were m i x t u r e s of isomers. All solvents mere reagents with a p u r i t y that was suitable for p e s t i c i d e residue analysis. P u r i f i e d m a t e r was p r e p a r e d using a Yamato Hodel VA-715 auto-still e q u i p p e d with filter, distiller, and ion exchanger. Each amount of OPE was placed in a 200-mL flask and I00 mL of p u r i f i e d water was added. Then, the OPE was d i s s o l v e d or d i s p e r s e d by u l t r a s o n i c a t i o n for I h. The s o l u t i o n was placed in the reactor, and 1900 mL of p u r i f i e d mater was added to the solution while it sas being stirred with a m a g n e t i c stirrer. After 30 min of stirring, 200 mL of the s o l u t i o n was taken as a reference solution and the r e m a i n i n g s o l u t i o n was a d j u s t e d to a desired pH with HCI or NaOH. The UV lamp was switched on. A 100-mL s u b s a m p l e of the irradiated s o l u t i o n was p e r i o d i c a l l y w i t h d r a w n during irradiation. Each s u b s a m p l c w i t h d r a w n was stored in the dark at 5 "C after a d j u s t i n g the s o l u t i o n to pH 3 with HCI. UY i n t e n s i t y was checked by using an UYP Hodel UVX r a d i o m e t e r having 254, 297, and 365 nm sensors. These values on the surface in the center of lamp were 6.6406.800, 0.140-0.143, and 0 . 1 5 3 - 0 . 1 5 8 mN/cm 2, respectively. TOC, IC, and pH were measured by the methods of J a p a n e s e Industrial Standard (Japan Industrial S t a n d a r d s C o m m i t t e e 1986). P h o s p h o r i c acid, CI- ion, and p h e n o l s mere m e a s u r e d by the A s c o r b i c Acid Hethod (American Public H e a l t h A s s o c i a t i o n et al. 1975), the Hohr Hethod ( E n v i r o n m e n t a l Health Bureau 1978a), and the 4 - A m i n o a n t i p y r i n e H e t h o d (Environmental H e a l t h Bureau 1978b), respectively.
369
At pH 3
At pH 10
~100l )
LU50~
n 0
0 0 1 2 3 4 5 6 -rime(h) Figure l D e g r a d a t i o n of 0PEs c o n c e n t r a t i o n is 0.1 mg/L, O A CRP, 9 TPP, [] TCP.
1--
!
at pH 3 and 10. TBP, 9 TCPP, ~
"r
!
I
!
Each 0PE TCEP, ~ TOP,
h 5 0 -m L p o r t i o n of each subsample withdrawn during the study was s a t u r a t e d w i t h NaC1. The OPE was e x t r a c t e d w i t h two lO-mL p o r t i o n s of dichloromethane. The e x t r a c t s were combined. The c o m b i n e d e x t r a c t was d r i e d over anhydrous Na2S04, concentrated until almost dry, reconstituted t o 2 mL with acetone, and a n a l y z e d by GC. One g r a m o f g 2 C 0 3 was a d d e d t o t h e s e c o n d 50-mL p o r t i o n of the subsample, a n d 1 mL o f a c e t i c anhydride was a d d e d t o t h e solution and thoroughly mixed at room temperature. After a few minutes, the acetylated compounds and other compounds were extracted w i t h 5 mL o f h e x a n e , an d t h e h e x a n e l a y e r was analyzed by GC o r GC-MS ( K r i j g s m a n a n d Ramp 1 9 7 7 ) .
RESULTS
AND D I S C U S S I O N
Figure 1 shows the disappearance curves o f e a c h OPE a t t h e concentration o f 0 . 1 m g / L a t pH 3 a n d l O . The c o n c e n t r a t i o n o f e a c h OPE d e c r e a s e d exponentially with time, and t h e r a t e o f OPE d i s a p p e a r a n c e was r e p r e s e n t e d by a f i r s t - o r d e r -d[OPEJ/dt = k lOPE] process. The v a l u e s of the pseudo-first-order rate constant k o f TBP, TCPP, TCEP, TOP, CRP, TPP, an d TCP d e t e r m i n e d from the plot of data points(in [ O P E ] / [ O P E ] o v s . t i m e ) w e r e >15, 2.3, 5.1, 3.0, 0.73, > 4 0 , a n d >20 h - I a t pH 3 a n d > l O , 4 . 5 , 4.1, 1.5, 1 . 6 , > 4 0 , a n d >15 h -1 a t pH 1 0 , r e s p e c t i v e l y . Aryl phosphates, TPP a n d TCP, w h i c h h a d l a r g e m o l a r extinction coefficients i n t h e r a n g e o f 2 3 0 - 2 8 0 nm d u e t o the benzene ring were more degradable than the other O P Es. 370
A l l OPEs, e s p e c i a l l y chloroalkyl phosphates, became more degradable a t pH 3 a n d 10 t h a n w i t h o u t pH a d j u s t m e n t . Th e d e g r a d a t i o n of TCEP, CRP, TPP, and TCP at pH lO may involve the h y d r o l y s i s with NaOH (Ishikaua et al. 1985b).
A l t h o u g h the s u b s t r a t e d i s a p p e a r a n c e was r e l a t i v e l y fast, it is n e c e s s a r y to clarify the d e g r a d a t i o n process, p a r t i c u l a r l y with regard to t o x i c - s u b s t a n c e formation. Therefore, the UV irradiation of OPEs at high c o n c e n t r a t i o n (3 x 10 -4 mole/L) was p e r f o r m e d without pH adjustment or at initial pH 12, and the p h o t o d e c o m p o s i t i o n products were identified. Phosphoric acid, C1- i o n , and p h e n o l s were produced, and t h e pH v a l u e d e c r e a s e d with the decrease i n t h e OPE concentration. The c h a n g e s o f e a c h i t e m a r e shown in F i g u r e 3. At a h i g h OPE c o n c e n t r a t i o n o f 3 x 10 - 4 m o l e / L , the degradation o f OPE w a s d e l a y e d . The t i m e s o f 8 0 ~ OPE d i s a p p e a r a n c e were
~l=nvironrnenll;al ~Contarnirmll;ion l a n d "lllaxicxalo~]
Photochemical Behavior of Organic Phosphate Esters in Aqueous Solutions Irradiated with a Mercury Lamp Seiichi Ishikawa, 1 Yutaka Uchimura, 2 Kenzo Baba, 2 Yoshio Eguchi, 1 and Kozo Kido ~ ~Kitakyushu Municipal Institute of Environmental Health Sciences, Shinike 1-2-1, Tobata Kitakyushu Fukuoka, 804, Japan and 2Water Quality Control Division, Kitakyushu Municipal Sewerage Bureau, Nish minato 96-3, Kokurak ta, Kitakyushu, Fukuoka, 804, Japan Pollution by t o x i c chemicals that are resistant to biological degradation and h a v e a p o t e n t i a l for accumulation in biological organisms is becoming a world-wide problem. Organic phosphate esters(OPEs) are widely used as plasticizers, industrial hydraulic fluids, an d l u b r i c a n t additives. Various OPEs h a v e b e e n d e t e c t e d in environmental samples (Tachikama et 1977; Ishikama et al. mastewaters (Ishikawa
al. 1975; Office of Health Studies 1985c) and in industrial and d o m e s t i c et al. 1985a).
Ultraviolet(UV) irradiation i s known as a e f f e c t i v e treatment for persistent chemicals in natural water wastewater ( C r o s b y a n d Hamadmad 1 9 7 1 ; T i s s o t et al.
or 1984).
Therefore, in order to develop a means o f r e m o v a l o f 0PEs i n mater, some f u n d a m e n t a l experiments w i t h OV i r r a d i a t i o n were performed w i t h a m e r c u r y l a m p , and p h o t o c h e m i c a l behaviors an d p h o t o d e c o m p o s i t i o n products were examined for 7 0PEs, namely tributyl phosphate(TBP), tris(chloropropyl) phosphate (TCPP), tris(2-chloroethyl) phosphate(TCEP), trioctyl phosphate(TOP), tris(dichloropropyl) phosphate(CRP), triphenyl
phosphate(TPP),
MATERIALS
AND METHODS
and
tricresyl
phosphate(TCP).
The r e a c t o r used in these experiments was a T a i k a K o g y o M o d e l HLV-A e q u i p p e d w i t h a 15 W l o w - p r e s s u r e mercury lamp. The g a s c h r o m a t o g r a p h ( t i C ) was a N i h o n D e n s h i M o d e l JfiC-2OK equipped with a flame ionization detector and a flame photometric detector having a 526-nm filter. Th e tic conditions were as follows: 2 mm i . d . x 2 m glass column p a c k e d w i t h 2~ 0 V - 1 7 § 2~ P Z - 1 7 9 c o a t e d on 6 0 - 8 0 m e s h
Send
reprint
request
to
S.
Ishikawa.
368
Uniport HPS; inlet temperature, 300 "C; column temperature, 100-300 "C and 200-300 "C(10 "C/min); c a r r i e r gas, 20 mL/min of n i t r o g e n gas; d e t e c t o r temperature, 300 "C. GC-mass spectrometer(GC-HS) was a N i h o n Denshi Hodel J H S - D X 303. The o p e r a t i o n a l c o n d i t i o n s had the same column and column t e m p e r a t u r e was p r o g r a m m e d from 100 to 280 "C at I0 "C/min. Inlet temperature was 2 9 0 " C . T h e h e l i u m f l o w r a t e w a s 10 mL/min. Ionizing e n e r g y mas 70 eV. Total organic carbon (TOC) a n d i n o r g a n i c carbon(IC) were measured with a Beckman H o d e l 915A TOC a n a l y z e r . Seven OPEs mere o b t a i n e d from Tokyo Chemical Co. TBP, TCEP, TOP, and TCP were p u r i f i e d by d i s t i l l a t i o n under reduced pressure. TCPP and CRP mere used without further purification. TPP was p u r i f i e d by zone refining. The purity of these OPEs was checked by GC. TCPP, CRP, and TCP were m i x t u r e s of isomers. All solvents mere reagents with a p u r i t y that was suitable for p e s t i c i d e residue analysis. P u r i f i e d m a t e r was p r e p a r e d using a Yamato Hodel VA-715 auto-still e q u i p p e d with filter, distiller, and ion exchanger. Each amount of OPE was placed in a 200-mL flask and I00 mL of p u r i f i e d water was added. Then, the OPE was d i s s o l v e d or d i s p e r s e d by u l t r a s o n i c a t i o n for I h. The s o l u t i o n was placed in the reactor, and 1900 mL of p u r i f i e d mater was added to the solution while it sas being stirred with a m a g n e t i c stirrer. After 30 min of stirring, 200 mL of the s o l u t i o n was taken as a reference solution and the r e m a i n i n g s o l u t i o n was a d j u s t e d to a desired pH with HCI or NaOH. The UV lamp was switched on. A 100-mL s u b s a m p l e of the irradiated s o l u t i o n was p e r i o d i c a l l y w i t h d r a w n during irradiation. Each s u b s a m p l c w i t h d r a w n was stored in the dark at 5 "C after a d j u s t i n g the s o l u t i o n to pH 3 with HCI. UY i n t e n s i t y was checked by using an UYP Hodel UVX r a d i o m e t e r having 254, 297, and 365 nm sensors. These values on the surface in the center of lamp were 6.6406.800, 0.140-0.143, and 0 . 1 5 3 - 0 . 1 5 8 mN/cm 2, respectively. TOC, IC, and pH were measured by the methods of J a p a n e s e Industrial Standard (Japan Industrial S t a n d a r d s C o m m i t t e e 1986). P h o s p h o r i c acid, CI- ion, and p h e n o l s mere m e a s u r e d by the A s c o r b i c Acid Hethod (American Public H e a l t h A s s o c i a t i o n et al. 1975), the Hohr Hethod ( E n v i r o n m e n t a l Health Bureau 1978a), and the 4 - A m i n o a n t i p y r i n e H e t h o d (Environmental H e a l t h Bureau 1978b), respectively.
369
At pH 3
At pH 10
~100l )
LU50~
n 0
0 0 1 2 3 4 5 6 -rime(h) Figure l D e g r a d a t i o n of 0PEs c o n c e n t r a t i o n is 0.1 mg/L, O A CRP, 9 TPP, [] TCP.
1--
!
at pH 3 and 10. TBP, 9 TCPP, ~
"r
!
I
!
Each 0PE TCEP, ~ TOP,
h 5 0 -m L p o r t i o n of each subsample withdrawn during the study was s a t u r a t e d w i t h NaC1. The OPE was e x t r a c t e d w i t h two lO-mL p o r t i o n s of dichloromethane. The e x t r a c t s were combined. The c o m b i n e d e x t r a c t was d r i e d over anhydrous Na2S04, concentrated until almost dry, reconstituted t o 2 mL with acetone, and a n a l y z e d by GC. One g r a m o f g 2 C 0 3 was a d d e d t o t h e s e c o n d 50-mL p o r t i o n of the subsample, a n d 1 mL o f a c e t i c anhydride was a d d e d t o t h e solution and thoroughly mixed at room temperature. After a few minutes, the acetylated compounds and other compounds were extracted w i t h 5 mL o f h e x a n e , an d t h e h e x a n e l a y e r was analyzed by GC o r GC-MS ( K r i j g s m a n a n d Ramp 1 9 7 7 ) .
RESULTS
AND D I S C U S S I O N
Figure 1 shows the disappearance curves o f e a c h OPE a t t h e concentration o f 0 . 1 m g / L a t pH 3 a n d l O . The c o n c e n t r a t i o n o f e a c h OPE d e c r e a s e d exponentially with time, and t h e r a t e o f OPE d i s a p p e a r a n c e was r e p r e s e n t e d by a f i r s t - o r d e r -d[OPEJ/dt = k lOPE] process. The v a l u e s of the pseudo-first-order rate constant k o f TBP, TCPP, TCEP, TOP, CRP, TPP, an d TCP d e t e r m i n e d from the plot of data points(in [ O P E ] / [ O P E ] o v s . t i m e ) w e r e >15, 2.3, 5.1, 3.0, 0.73, > 4 0 , a n d >20 h - I a t pH 3 a n d > l O , 4 . 5 , 4.1, 1.5, 1 . 6 , > 4 0 , a n d >15 h -1 a t pH 1 0 , r e s p e c t i v e l y . Aryl phosphates, TPP a n d TCP, w h i c h h a d l a r g e m o l a r extinction coefficients i n t h e r a n g e o f 2 3 0 - 2 8 0 nm d u e t o the benzene ring were more degradable than the other O P Es. 370
A l l OPEs, e s p e c i a l l y chloroalkyl phosphates, became more degradable a t pH 3 a n d 10 t h a n w i t h o u t pH a d j u s t m e n t . Th e d e g r a d a t i o n of TCEP, CRP, TPP, and TCP at pH lO may involve the h y d r o l y s i s with NaOH (Ishikaua et al. 1985b).
A l t h o u g h the s u b s t r a t e d i s a p p e a r a n c e was r e l a t i v e l y fast, it is n e c e s s a r y to clarify the d e g r a d a t i o n process, p a r t i c u l a r l y with regard to t o x i c - s u b s t a n c e formation. Therefore, the UV irradiation of OPEs at high c o n c e n t r a t i o n (3 x 10 -4 mole/L) was p e r f o r m e d without pH adjustment or at initial pH 12, and the p h o t o d e c o m p o s i t i o n products were identified. Phosphoric acid, C1- i o n , and p h e n o l s were produced, and t h e pH v a l u e d e c r e a s e d with the decrease i n t h e OPE concentration. The c h a n g e s o f e a c h i t e m a r e shown in F i g u r e 3. At a h i g h OPE c o n c e n t r a t i o n o f 3 x 10 - 4 m o l e / L , the degradation o f OPE w a s d e l a y e d . The t i m e s o f 8 0 ~ OPE d i s a p p e a r a n c e were
