Photochemistry of Environmental Aquatic Systems - American

Chapter 3

Photolysis of Phenol and Chlorophenols in Estuarine Water 1

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Huey-Min Hwang , R. E. Hodson , and R. F. Lee 1

Department of Microbiology and Institute of Ecology, University of Georgia, Athens, GA 30602 Skidaway Institute of Oceanography, P.O. Box 13687, Savannah, GA 31416

Downloaded by UNIV ILLINOIS URBANA on March 8, 2013 | http://pubs.acs.org Publication Date: December 8, 1987 | doi: 10.1021/bk-1987-0327.ch003

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Phenol and a number of chlorophenols at a concentration of 25 μg L in estuarine water were exposed to sun light. The relative rates of photolysis decreased in the order 2,4,5-trichlorophenol, 2,4-dichlorophenol, pentachlorophenol, p-chlorophenol, and phenol. The photo-trans formation rate constants for dichlorophenol, trichlorophenol and pentachlorophenol ranged from 0.3 to 1.2 hr with half-lives ranging from 0.6 to 3 hr (light hours). Phenol and chlorophenol had half-lives ranging from 43 to 118 hr. Similar differences were observed for photo-mineralization with half-lives ranging from 6 to 14 days for dichlorophenol, trichlorophenol, and pentachlorophenol and 16 to 334 days for phenol and p-chlorophenol. Changes in pH, season, and cloud cover were among the factors to affect photolysis rates. At a pH below the pK the photolysis rate was much lower due to a higher rate of photolysis for the phenoxide ion rela tive to the nonionized form. A decrease in the midday irradiance from 5.4 to 2.6 Einsteins/m /hr, due to cloud cover, resulted in photolysis rate constants of trichlorophenol decreasing from 1.07 to 0.30 hr . Highest photolysis rates for all compounds were found in the summer, presumably due to the surface irradi ance increase with much of this increase due to a shift in short wavelength light. Higher concentrations of suspended particulates in the summer resulted in a 4-fold higher diffuse attenuation coefficient at 330 nm in the summer compared with the winter. Thus, while surface irradiance increased in the summer the attenu ation of this light in the water increased during this season due to higher levels of particulates. For sur face waters the increase in summer irradiance affected photolysis rates more than the attenuation by partic ulates. With the exception of dichlorophenol and pentach lorophenol, the photolysis rate of the compounds was -1

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0097-6156/87/0327-0027$06.00/0 © 1987 American Chemical Society

In Photochemistry of Environmental Aquatic Systems; Zika, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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similar in both distilled and estuarine water when the screening factor, i.e., attenuation of light, of estu arine water was taken into account. The higher photo lysis rate of 2,4-dichlorophenol in estuarine water relative to distilled water suggested a photo-sensi tized reaction. The lower photolysis rate of penta chlorophenol in estuarine water relative to distilled water was due to inhibition of photolysis by chloride ion. C h l o r o p h e n o l s e n t e r e s t u a r i e s through t h e i r use i n i n d u s t r y and a g r i c u l t u r e . F o r example, the e f f l u e n t s from the p u l p and paper i n d u s t r y c o n t a i n c h l o r o p h e n o l s and more c h l o r i n a t e d phenols form downstream due t o the r e a c t i o n between c h l o r i n e i n b l e a c h i n g l i q u o r s and phenols d e r i v e d from wood e x t r a c t i v e s (_1 ). A number o f s t u d i e s have shown d i f f e r e n c e s i n the p h o t o l y s i s r a t e s o f x e n o b i o t i c s b e t ween n a t u r a l and d i s t i l l e d w a t e r , these d i f f e r e n c e s r e s u l t from p a r t i c u l a t e and d i s s o l v e d substances i n n a t u r a l waters which i n f l u e n c e p h o t o l y s i s o f x e n o b i o t i c s through a t t e n u a t i o n o f s u n l i g h t , secondary p h o t o r e a c t i o n s , and c h e m i c a l or p h y s i c a l i n t e r a c t i o n s t h a t change the s p e c i a t i o n o r a v a i l a b i l i t y o f the x e n o b i o t i c s (2). Some examples i n c l u d e the g r e a t l y a c c e l e r a t e d p h o t o c h e m i c a l d e g r a d a t i o n o f p a r a t h i o n i n r i v e r or swamp water r e l a t i v e t o d i s t i l l e d water ( 3 ) and the absence o f p h o t o l y s i s o f the h e r b i c i d e m o l i n a t e i n d i s t i l l e d water b u t r a p i d p h o t o l y s i s i n n a t u r a l waters ( 4 ) . I n c o n t r a s t , t h e p h o t o l y s i s r a t e of p e n t a c h l o r o p h e n o l i s slower i n seawater than i n d i s t i l l e d water due t o the p h o t o n u c l e o p h i l i c s u b s t i t u t i o n o f c h l o r i d e ions i n seawater f o r c h l o r i d e i n p e n t a c h l o r o p h e n o l ( 5 ) . I n s t e a d of b e i n g a s e n s i t i z e r , the humic substances i n n a t u r a l waters can a l s o a c t as quenchers i n the p h o t o l y s i s o f some p o l y a r o m a t i c hydrocarbons (6). The p h o t o l y s i s o f phenols i s a f f e c t e d by pH changes, s i n c e p h e n o l i c compounds d i s s o c i a t e t o phenoxide ions i n b a s i c w a t e r s , r e s u l t i n g i n a l t e r e d p h o t o r e a c t i v i t i e s (_7 ). Many phot o l y s i s s t u d i e s have l i m i t e d the l i g h t source t o a p a r t i c u l a r i n t e n s i t y and a n a r r o w l y d e f i n e d wavelength band. While t h i s s i m p l i f i e s i n t e r p r e t a t i o n o f r e s u l t s , i t can prevent e x t r a p o l a t i o n o f l a b o r a tory data t o n a t u r a l environmental c o n d i t i o n s . Z i k a (&) has p o i n t e d out t h a t l i m i t i n g the wavelength o f r a d i a t i o n o f t e n reduces t h e number o f p o s s i b l e r e a c t i o n r o u t e s and t h a t the l i g h t i n t e n s i t y a f f e c t s the s t e a d y - s t a t e c o n c e n t r a t i o n s o f r e a c t i v e t r a n s i e n t s i n the s o l u t i o n which can a f f e c t the secondary r e a c t i o n r a t e s . I n n a t u r a l waters p h o t o c h e m i c a l r e a c t i o n s are a f f e c t e d by changes i n s u n l i g h t i n t e n s i t y and wavelength a s s o c i a t e d w i t h season and time o f day, amount o f d i s s o l v e d and p a r t i c u l a t e substances and presence o f photosensitizers. The o b j e c t i v e s o f t h i s s t u d y were t o determine the p h o t o l y s i s r a t e s o f phenol and some c h l o r o p h e n o l s i n e s t u a r i n e and d i s t i l l e d water under n a t u r a l s u n l i g h t c o n d i t i o n s . E f f e c t s o f s u n l i g h t i r r a d i a n c e , pH, and c h l o r i d e ions c o n c e n t r a t i o n on p h o t o l y s i s r a t e s were d e t e r m i n e d . S p e c t r a l data and s u n l i g h t p h o t o l y s i s r a t e c o n s t a n t s o f both the a c t i n o m e t e r and the c h l o r o p h e n o l s were used t o c a l c u l a t e the apparent quantum y i e l d s o f the v a r i o u s chlorophenols.


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Photolysis of Phenol and Chlorophenob

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M a t e r i a l s and Methods


Sample C o l l e c t i o n . S u r f a c e water samples were c o l l e c t e d from S k i d away R i v e r , an e s t u a r i n e r i v e r near Savannah, G e o r g i a . Water samples (4 l i t e r s ) were taken i n acid-washed, 2.5 g a l . p o l y e t h y l e n e c o n t a i n e r s . Assays were i n i t i a t e d w i t h i n one hour o f c o l l e c t i o n . Temper a t u r e , pH, and s a l i n i t y were measured a t the time samples were c o l lected. Reagents. R i n g - U L - ^ C - l a b e l e d p - c h l o r o p h e n o l (11.61 mci/mM), 2,4d i c h l o r o p h e n o l (10.7 mci/mM), and 2 , 4 , 5 - t r i c h l o r o p h e n o l (0.80 mci/mM) were o b t a i n e d from P a t h f i n d e r L a b o r a t o r i e s I n c . Ring-UL-^C-labeled phenol (58 mci/mM) and p e n t a c h l o r o p h e n o l (8.8 mci/mM) were o b t a i n e d from C a l i f o r n i a B i o n u c l e a r Corp. P u r i t y ranged from 95% t o 99%. U n l a b e l e d compounds and valerophenone (99% pure) were o b t a i n e d from A l d r i c h Chemical Company. M a l a c h i t e green l e u c o c y a n i d e a c t i n o m e t e r (MGLC) was o b t a i n e d as a g i f t from Dr. R.G. Zepp o f t h e Environmen t a l P r o t e c t i o n Agency (Athens, G e o r g i a ) . I n c u b a t i o n and D e g r a d a t i o n Measurements. R a d i o l a b e l e d or u n l a b e l e d compounds were d i s s o l v e d i n acetone and added t o 60 ml o f e s t u a r i n e or p h o s p h a t e - b u f f e r e d d i s t i l l e d water (pH 7.7 ± 0.2; 16 mM) i n 150 ml q u a r t z f l a s k s (Quartz S c i e n t i f i c , I n c . ) . Acetone was a t a f i n a l c o n c e n t r a t i o n o f 1 χ 10"^M and t h e r e was no p h o t o s e n s i t i z a t i o n o f the compounds by acetone i n d i s t i l l e d water. These f l a s k s a l l o w more than 85% t r a n s m i s s i o n o f l i g h t o f wavelength l o n g e r than 260 nm. A p p r o x i m a t e l y 0.1 y c i o f the s e l e c t e d compound was added t o each f l a s k . The f i n a l c o n c e n t r a t i o n o f each compound i n the f l a s k s was a d j u s t e d t o 25 yg L~* by the a d d i t i o n o f u n l a b e l e d compound. The f l a s k s were suspended i n an outdoor tank c o n t a i n i n g f l o w i n g e s t u a r i n e w a t e r . F l a s k s were suspended 3 cm below t h e s u r f a c e . Dark c o n t r o l s c o n s i s t e d o f f l a s k s covered w i t h aluminum f o i l . A l l samples c o n t a i n e d formaldehyde (0.4%) t o prevent m i c r o b i a l degrada t i o n o f the compounds. U l t r a v i o l e t a b s o r p t i o n by t h e formaldehyde s o l u t i o n a t t h i s c o n c e n t r a t i o n was n e g l i g i b l e . A t v a r i o u s times the amount o f parent compound degraded ( p h o t o - t r a n s f o r m a t i o n ) and p r o d u c t i o n o f ^^C0£ ( p h o t o - m i n e r a l i z a t i o n ) were d e t e r m i n e d . Since phenol and p - c h l o r o p h e n o l p h o t o l y z e d s l o w l y , they were exposed t o s u n l i g h t f o r up t o 3 days, w h i l e the o t h e r c h l o r o p h e n o l s were exposed t o midday s u n l i g h t (between 10:00 and 14:00) f o r photot r a n s f o r m a t i o n s t u d i e s . Water samples f o r p h o t o - m i n e r a l i z a t i o n s t u d i e s were i n c u b a t e d f o r 24, 48, or 72 hr t o a l l o w f o r t h e accumu l a t i o n o f enough ^^C0£ t o measure. The ^ C 0 2 produced was determined as d e s c r i b e d i n e a r l i e r work (j), 10). To determine l o s s o f parent compound ( p h o t o - t r a n s f o r m a t i o n ) , each sample was a c i d i f i e d w i t h 4N H2SO4 t o pH 2 and the parent compound and i t s d e g r a d a t i o n p r o ducts were e x t r a c t e d w i t h e t h y l a c e t a t e . E x t r a c t i o n e f f i c i e n c y f o r the parent compounds averaged g r e a t e r than 95%. The e x t r a c t s were c o n c e n t r a t e d and a p p l i e d t o s i l i c a g e l t h i n - l a y e r chromatography p l a t e s (E. Merck) u s i n g a s o l v e n t system o f hexane: acetone ( 1 : 1 , v o l : v o l ) . Parent compounds and t h e i r d e g r a d a t i o n products were scraped from t h i n - l a y e r p l a t e s and t h e i r r a d i o a c t i v i t y determined w i t h a s c i n t i l l a t i o n c o u n t e r (Packard TRI-carb-300C). The a n a l y s i s of the m a l a c h i t e green l e u c o c y a n i d e a c t i n o m e t e r was c a r r i e d out


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u s i n g the procedures d e s c r i b e d by M i l l e r and Zepp ( 1 1 ) . The s c r e e n i n g f a c t o r was determined by e x p o s i n g valerophenone s o l u t i o n s (10 μΜ) t o midday s u n l i g h t (12) f o r v a r i o u s p e r i o d s up t o 1 h r . A n a l y s e s f o r valerophenone were conducted w i t h h i g h p r e s s u r e l i q u i d chromatography u s i n g a M i c r o m e r i t i c e Model 7000B equipped w i t h a 4.6x250 mm r e v e r s e - p h a s e column o f 10 μm ODS/Spherisorb (mobil phase 70:30 methanol/water, f l o w r a t e 2.0 ml min"*, d e t e c t o r wavelength 260 nm). Procedures f o r K i n e t i c S t u d i e s . T r i p l i c a t e s of each r a d i o l a b e l e d compound and d u p l i c a t e s o f valerophenone s o l u t i o n were exposed t o s u n l i g h t . P h o t o - t r a n s f o r m a t i o n and p h o t o - m i n e r a l i z a t i o n r a t e c o n s t a n t s were c a l c u l a t e d assuming t h a t the r e a c t i o n s were f i r s t - o r d e r . The r a t e c o n s t a n t s were c o r r e c t e d f o r a b i o t i c dark d e g r a d a t i o n (always l e s s than 5% o f t o t a l ) and a t t e n u a t i o n o f s u n l i g h t by d i s s o l v e d o r g a n i c m a t e r i a l i n the e s t u a r i n e water samples. U n l e s s s p e c i f i e d , p h o t o l y s i s r a t e c o n s t a n t s and h a l f - l i v e s of the compounds were determined d u r i n g sunny days. S o l a r r a d i a t i o n was determined w i t h a r a d i o m e t e r (LI-COR I n c . , Model LI-550B; a c t i v e r a n g e , 400-700 nm). The l i g h t s c r e e n i n g f a c t o r (S) was assumed t o be equal t o the r a t i o of the valerophenone p h o t o l y s i s r a t e c o n s t a n t i n p a r t i c u l a t e f r e e e s t u a r i n e water t o the p h o t o l y s i s r a t e c o n s t a n t i n d i s t i l l e d water ( 1 3 ) . P r o p e r t i e s o f E s t u a r i n e Water. The c o n c e n t r a t i o n o f suspended p a r t i c u l a t e s i n e s t u a r i n e water was determined by f i l t e r i n g 1 l i t e r o f water through p r e - d r i e d and pre-weighed g l a s s f i b e r f i l t e r s (GF/C, Whatman). The f i l t e r s c o n t a i n i n g p a r t i c u l a t e s were d r i e d and weighed. An e s t u a r i n e water sample was u l t r a c e n t r i f u g e d a t 100,000 xg f o r 1 h r t o o b t a i n p a r t i c u l a t e - f r e e water (Beckman U l t r a c e n t r i fuge Model L 5 - 4 0 ) . The p a r t i c u l a t e - f r e e e s t u a r i n e water was used i n d e t e r m i n i n g the s c r e e n i n g f a c t o r . U l t r a v i o l e t a b s o r p t i o n s p e c t r a o f the p a r t i c u l a t e - f r e e e s t u a r i n e water were o b t a i n e d w i t h a s p e c t r o photometer (Beckman Model DU-6). The d i f f u s e a t t e n u a t i o n c o e f f i c i ents (K) a t 330 nm (the c o e f f i c i e n t s d e r i v e d from d i r e c t measure ments o f s o l a r i r r a d i a n c e a t v a r i o u s depths i n a water body) o f t h e e s t u a r i n e water were determined u s i n g m a l a c h i t e green l e u c o c y a n i d e , by the methods d e s c r i b e d by M i l l e r and Zepp ( 1 1 ) . The component o f Κ from the d i s s o l v e d substances was c a l c u l a t e d by m u l t i p l y i n g a b s o r bance of p a r t i c u l a t e - f r e e e s t u a r i n e water by 2.303 and the d i s t r i b u t i o n f u n c t i o n (D) ( 1 4 ) . D r e f e r s t o the mean p a t h l e n g t h o f l i g h t i n an h o r i z o n t a l l a y e r o f the water sample d i v i d e d by t h i c k n e s s o f t h e l a y e r ( 1 1 ) , and i n our experments i t was 1.1. F o r a n a l y s i s o f p a r t i c u l a t e o r g a n i c carbon and p a r t i c u l a t e n i t r o g e n , 500 ml o f water was passed s e q u e n t i a l l y through two Gelman type A g l a s s f i b e r f i l t e r s which has been precombusted a t 500°C. The f i l t e r s were r i n s e d w i t h 0.01 N HC1 t o remove i n o r g a n i c carbon and d r i e d and s t o r e d i n a 60°C oven. P a r t i c u l a t e o r g a n i c carbon on the f i l t e r s was determined by t h e methods of Menzel and Vaccaro ( 1 5 ) . P a r t i c u l a t e o r g a n i c n i t r o g e n was determined by t h e c l a s s i c a l micro-Dumas method as d e s c r i b e d by S t r i c k l a n d and Parsons ( 1 6 ) . The a n a l y s i s o f d i s s o l ved o r g a n i c carbon c o n s i s t e d o f the wet o x i d a t i o n o f f i l t e r e d e s t u a r i n e water by p o t a s s i u m p e r s u l f a t e i n a s e a l e d g l a s s ampoule. Samples were s u b s e q u e n t l y a n a l y z e d by t h e methods o f Menzel and


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Vaccaro ( 1 5 ) . N i t r a t e and phosphate were a n a l y z e d by methods d e s c r i b e d by S t r i c k l a n d and Parsons ( 1 6 ) . Apparent Quantum Y i e l d (0 ) of the D i r e c t P h o t o l y s i s of C h i o r o p h e n o l s . The s p e c t r a l data and s u n l i g h t p h o t o l y s i s r a t e c o n s t a n t s of both a c t i n o m e t e r valerophenone and the compound, and r e a c t i o n quantum y i e l d of valerophenone were used t o c a l c u l a t e 0 of c h l o r o phenols u s i n g GCSOLAR program ( 1 3 ) . r

r


Results P h o t o l y s i s of v a r i o u s c h l o r o p h e n o l s as a f u n c t i o n of time a r e shown i n F i g . 1. The p h o t o - t r a n s f o r m a t i o n and p h o t o - m i n e r a l i z a t i o n of the compounds f o l l o w e d a f i r s t - o r d e r e q u a t i o n In ( C /C) * k p t , where C and C are the c o n c e n t r a t i o n s of the compound a t time zero and time t , w h i l e kp i s the f i r s t - o r d e r p h o t o l y s i s r a t e c o n s t a n t . The photol y s i s h a l f - l i v e s of the compounds were c a l c u l a t e d u s i n g the e q u a t i o n t-1/2 = 0.693/kp. The r e l a t i v e r a t e s of p h o t o l y s i s i n e s t u a r i n e water decreased i n the o r d e r 2 , 4 , 5 - t r i c h l o r o p h e n o l , 2 , 4 - d i c h l o r o p h e n o l , p e n t a c h l o r o p h e n o l , p - c h l o r o p h e n o l , phenol (Table I ) . The p h o t o - t r a n s f o r m a t i o n r a t e c o n s t a n t s f o r 2 , 4 - d i c h l o r o p h e n o l , 2 , 4 . 5 - t r i c h l o r o p h e n o l , and p e n t a c h l o r o p h e n o l ranged from 0.3 t o 1.2 h r " l w i t h h a l f - l i v e s r a n g i n g from 0.6 t o 3 hr ( l i g h t h o u r s ) . Phenol and p - c h l o r o p h e n o l were more r e s i s t a n t t o p h o t o l y s i s and t h e i r h a l f l i v e s ranged from 43 t o 118 h r . S i m i l a r d i f f e r e n c e s were observed f o r p h o t o - m i n e r a l i z a t i o n w i t h h a l f - l i v e s r a n g i n g from 6 t o 14 days f o r d i c h l o r o p h e n o l , t r i c h l o r o p h e n o l , and p e n t a c h l o r o p h e n o l and 16 to 334 days f o r phenol and p - c h l o r o p h e n o l . These r e l a t i v e p h o t o l y s i s r a t e s would be p r e d i c t e d by the absorbance and r e a c t i o n quantum y i e l d s f o r the compounds as g i v e n i n Table I I . D i c h l o r o p h e n o l , t r i c h l o r o p h e n o l , and p e n t a c h l o r o p h e n o l had h i g h molar a b s o r p t i v i t i e s i n the u l t r a v i o l e t - b l u e r e g i o n w i t h absorbance maxima a t 304, 310, and 320 nm, r e s p e c t i v e l y . I n c o n t r a s t both phenol and c h l o r o p h e n o l had maxima i n the u l t r a v i o l e t a t 269 and 280 nm, r e s p e c t i v e l y . Listed i n o r d e r o f d e c r e a s i n g quantum y i e l d a r e t r i c h l o r o p h e n o l , d i c h l o r o p h e n o l , p - c h l o r o p h e n o l , and p e n t a c h l o r o p h e n o l . With the e x c e p t i o n of d i c h l o r o p h e n o l and p e n t a c h l o r o p h e n o l , the compounds p h o t o l y z e d a t about the same r a t e i n d i s t i l l e d and e s t u a r i n e water when the a t t e n u a t i o n of l i g h t , i . e . , s c r e e n i n g f a c t o r , by e s t u a r i n e water was taken i n t o account. Dichlorophenol photolyzed at a s i g n i f i c a n t l y h i g h e r r a t e i n e s t u a r i n e water than i n d i s t i l l e d w a t e r . The h i g h e r p h o t o l y s i s r a t e o f 2 , 4 - d i c h l o r o p h e n o l i n e s t u a r i n e water r e l a t i v e t o d i s t i l l e d water suggested t h a t the p h o t o l y s i s of d i c h l o r o p h e n o l i n e s t u a r y i n v o l v e d a p h o t o - s e n s i t i z e d r e a c t i o n . The p h o t o - t r a n s f o r m a t i o n r a t e o f p e n t a c h l o r o p h e n o l was s i g n i f i c a n t l y lower i n e s t u a r i n e r e l a t i v e t o d i s t i l l e d water (Table I ) . T h i s may have been due t o c h l o r i d e i o n s i n c e sodium c h l o r i d e added t o d i s t i l l e d water w i t h a f i n a l c o n c e n t r a t i o n o f 0.5 M ( s a l i n i t y 30 °/oo) i n h i b i t e d p h o t o l y s i s of p e n t a c h l o r o p h e n o l . P h o t o l y s i s of d i c h l o r o phenol and t r i c h l o r o p h e n o l were not a f f e c t e d by c h l o r i d e i o n a d d i tion. There was l i t t l e change i n the pH of the e s t u a r y d u r i n g the y e a r . When the pH of e s t u a r i n e or b u f f e r e d d i s t i l l e d water was changed, t h e r e were changes i n the p h o t o l y s i s r a t e c o n s t a n t s o f the Q


Q



F i g u r e 1. P h o t o l y s i s of c h l o r o p h e n o l s i n e s t u a r i n e water. C h l o r o p h e n o l s were added t o the water sample a t a c o n c e n t r a t i o n of 25 μ g L " l i n December. Temperature was 14°C and pH was 7.6. T r a n s f o r m a t i o n e q u a t i o n s were I n c 3.22-0.01 t ( p - c h l o r o p h e n o l ) , I n c = 3.22-0.44 t ( 2 , 4 - d i c h l o r o p h e n o l ) , I n c 3.220.65 t ( 2 , 4 , 5 - t r i c h l o r o p h e n o l ) , and I n c = 3.22-0.27 t ( p e n t a c h l o r o p h e n o l ) , where c i s the c o n c e n t r a t i o n of t h e c h l o r o p h e n o l at time t . V e r t i c a l bars r e p r e s e n t 1 standard d e v i a t i o n w i t h η = 3. 3

3



b

*

*

a

b

summer winter summer winter

(25) (ID (25) (11)

(25) (18) (25) (18)

(25) (ID (20) (25) (11) (20)

(25) (14) (25) (14)

(24) (10) (24) (10)

+ + + + 1.3 1.1 1.3 1.1

+ 0.2 + 1.0 + 0.5 • 0.2 • 0.4 + 0.5

5.2 1.9 5.2 1.9

+ + + + 1.5 0.8 1.5 0.8

5.3 + 0.5 2.3 + 1.2 5.3 + 0.5 1.2 2.3

5.7 1.8 2.8 5.7 2.5 2.8

5.9 + 0.6 2.7 1.3 5.9 + 0.6 2.7 + 1.3

4.9 2.9 4.9 2.9

8

0.6 0.37 0.37 0.27

1.3 0.61 1.2 0.65

0.82 0.21 0.19 1.00 0.38 0.37

+ 0.1 0.06 + 0.08 + 0.04

+ 0.2 0.08 + 0.3 + 0.06

+ 0.06 0.05 + 0.02 + 0.06 • 0.02 • 0.02

•

0.011 + 0.006 0.007 + 0.002 0.015 + 0.007 0.011 • 0.004

0.015 + 0.006 0.0040 • 0.0002 0.016 + 0.006 0.006 + 0.001

1 2 2 3

0.5 1 0.6 1

0.8 3 4 0.7 2 2

63 99 46 63

46 173 43 118

1

- 1

0.11 0.049 0.12 0.07

+ + •f +

0.04 0.008 0.05 0.01

6 14 6 10

7 14 6 14

6 14

0.12 • 0.05 0.05 + 0.01

0.10 + 0.03 0.050 + 0.009 0.12 + 0.04 0.05 • 0.01

8 14

58 224 53 334

16 169 16 110

0.09 + 0.03 0.049 + 0.005

0.012 + 0.003 0.003 • 0.002 0.013 + 0.004 0.0021 + 0.0005

0.04 + 0.02 0.0041 • 0.0005 0.04 • 0.02 0.0063 + 0.0008

Photo-mineralization Half-life Rate Constant (day) (day" )

D i s t i l l e d water was b u f f e r e d at pH 7.7 ± 0.2 (0.016 M

phosphate).

^ C - l a b e l e d compounds were incubated i n quartz f l a s k s at a c o n c e n t r a t i o n of 25 yg L . The f l a s k s with d i s t i l l e d or estuarine water were exposed during days when there was f u l l s u n l i g h t , i . e . , no c l o u d s . A l l samples were t r e a t e d with formaldehyde (0.4%). Values are expressed as the mean ± standard d e v i a t i o n (n = 3 ) . 2,4d i c h l o r o p h e n o l , 2 , 4 , 5 - t r i c h l o r o p h e n o l , and pentachlorophenol were exposed to midday s u n l i g h t f o r 4 h r , and h a l f l i v e s were reported as " l i g h t hours". Because of slower p h o t o l y s i s rates phenol and p-chlorophenol were exposed to s u n l i g h t and darkness f o r up to 3 days. Degradations of the compounds in darkness were n e g l i g i b l e .

es tuary

Pentachlorophenol distilled

es tuary


summer winter winter summer winter winter



Season (Temp. °C)

2,4,5-Trichlorophenol distilled

es tuary

2,4-Dichlorophenol distilled

estuary

p-Chlorophenol distilled

es tuary

distilled

Compound and Water

2

and C h l o r o p h e n o l s

Photo-trans format ion Half-life Rate Constant (hr) (hr-*)

P h o t o l y s i s of Phenol

Midday Surface Irradiance (Einsteins/m /hr)

Table I.


^

β.

I

5

Ζ Ο m H

0

3C

34


Table

I I . Molar A b s o r p t i v i t i e s and R e a c t i o n Quantum Y i e l d s P h o t o l y s i s of Phenol and C h l o r o p h e n o l s

((tr)

for Direct

a


Molar

A

(M" cra-M

Phenol

p-CP

Absorptivity DC Ρ

295

9

270

1813

2824

1902

297.5

7

161

1715

3219

1948

300

5

116

1683

3554

2134

302.5

3

97

1707

3851

2319

305

2

84

1707

4087

2644

307.5

1

64

1675

4285

2922

310

51

1585

4364

3154

312.5

32

1423

4305

3432

315

26

1171

4087

3757

317.5

19

986

3614

3943

320

618

2962

4035

323.1

350

2113

3803

65

553

2319

59

742

0.080

0.013

Wavelength, nm

330 340 R e a c t i o n Quant urn Yield 0 r b

0.066

0.075

TCP

PCP

• The measurements were conducted i n d i s t i l l e d water b u f f e r e d at pH 7.6. A b b r e v i a t i o n s : p-CP: p - c h l o r o p h e n o l , DCP: 2 , 4 - d i c h l o r o p h e n o l , TCP: 2 , 4 , 5 - t r i c h l o r o p h e n o l , PCP: p e n t a c h l o r o p h e n o l . . S p e c t r a l data and s u n l i g h t p h o t o l y s i s r a t e c o n s t a n t s o f both a c t i n o m e t e r v a l erophenone and c h l o r o p h e n o l s i n p h o s p h a t e - b u f f e r e d s o l u t i o n s (pH 7.6), and r e a c t i o n quantum y i e l d o f valerophenone were used to c a l c u l a t e 0 r o f c h l o r o phenols u s i n g GCSOLAR program ( S k u r l a t o v et a l . , 1983).


3.

HWANG ET AL.


35

c h l o r o p h e n o l s (Table I I I ) . H i g h e s t p h o t o l y s i s r a t e s were o b t a i n e d at h i g h pH (pH 10) where the c h l o r o p h e n o l s e x i s t as the phenoxide i o n . A t pH below the p K the p h o t o l y s i s r a t e s were r e l a t i v e l y low, thus the p h o t o l y s i s r a t e c o n s t a n t f o r d i c h l o r o p h e n o l was 0.13, 1.0, and 1.8 h r " a t pH 5.5, pH 7.6, and pH 10, r e s p e c t i v e l y . B o r o s i l i c a t e g l a s s i s o f t e n used i n p h o t o l y s i s s t u d i e s . However, s e c t i o n s of b o r o s i l i c a t e g l a s s were found to o n l y t r a n s m i t 50% of the l i g h t at 310 nm w h i l e q u a r t z s e c t i o n t r a n s m i t t e d 100% of t h i s l i g h t . T h e r e f o r e , f o r compounds which absorb u l t r a v i o l e t - b l u e l i g h t (280-320 nm), q u a r t z glassware i s n e c e s s a r y f o r p h o t o l y s i s s t u d i e s . F i g u r e 3 shows the p h o t o l y s i s of 2 , 4 , 5 - t r i c h l o r o p h e n o l i n b o r o s i l i c a t e and q u a r t z f l a s k s . The p h o t o l y s i s r a t e c o n s t a n t s were 0.74 h r " and 1.07 h r i n b o r o s i l i c a t e and q u a r t z , r e s p e c t i v e l y , which were shown t o be s i g n i f i c a n t l y d i f f e r e n t by a t - t e s t (p £ 0.05). A l l o t h e r p h o t o l y s i s s t u d i e s used q u a r t z f l a s k s . The p h y s i c a l and c h e m i c a l p r o p e r t i e s of the Skidaway R i v e r measured d u r i n g d i f f e r e n t times of the year are l i s t e d i n T a b l e IV. There were few changes d u r i n g the year i n pH, β3βη (absorbance of the p a r t i c u l a t e - f r e e e s t u a r i n e water at 330 nm) and the s c r e e n i n g f a c t o r . Other p r o p e r t i e s i n c l u d i n g c o n c e n t r a t i o n of suspended p a r t i c u l a t e s , K330 ( d i f f u s e a t t e n u a t i o n c o e f f i c i e n t a t 330 nm) and K ( s p e c i f i c a t t e n u a t i o n c o e f f i c i e n t due t o suspended p a r t i c u l a t e s ) v a r i e d s i g n i f i c a n t l y d u r i n g the y e a r . For examçle, K330 of the e s t u a r i n e water i n c r e a s e d from 0.05 to 0.22 cm~l from w i n t e r t o summer, showing t h a t u l t r a v i o l e t - b l u e l i g h t was a t t e n u a t e d by a f a c t o r of f o u r i n the summer. Thus, w h i l e s u r f a c e i r r a d i a n c e i n c r e a s e d going from w i n t e r t o summer (Table I ) the a t t e n u a t i o n of l i g h t by e s t u a r i n e water was g r e a t e r i n the summer, due t o h i g h conc e n t r a t i o n s of suspended p a r t i c u l a t e s (Table I V ) . As noted above p h o t o l y s i s r a t e s i n e s t u a r i n e water d e c r e a s e d i n the o r d e r t r i c h l o r o p h e n o l , d i c h l o r o p h e n o l , p e n t a c h l o r o p h e n o l , c h l o r o p h e n o l , and p h e n o l . With the e x c e p t i o n of the t r a n s f o r m a t i o n r a t e s f o r p - c h l o r o p h e n o l and the p h o t o l y s i s r a t e s f o r p e n t a c h l o r o p h e n o l , f o r a l l compounds the p h o t o l y s i s r a t e s i n c l u d i n g both p h o t o - t r a n s f o r m a t i o n and p h o t o - m i n e r a l i z a t i o n were h i g h e r i n the summer than i n the w i n t e r ( t - t e s t , ρ £ 0.05; T a b l e I , F i g . 2 ) . For example, the p h o t o - t r a n s f o r m a t i o n r a t e c o n s t a n t of d i c h l o r o p h e n o l i n c r e a s e d from 0.38 to 1.00 h r " going from w i n t e r t o summer, and the photo-miner a l i z a t i o n r a t e c o n s t a n t of phenol i n c r e a s e d from 0.006 to 0.04 day" g o i n g from w i n t e r t o summer. I n a d d i t i o n to changes i n s u n l i g h t i r r a d i a n c e d u r i n g d i f f e r e n t seasons, t h e r e are a l s o changes i n the i r r a d i a n c e d u r i n g the same season, e.g., c l o u d c o v e r . F i g . 3 compares the p h o t o l y s i s r a t e of t r i c h l o r o p h e n o l on a sunny and o v e r c a s t day i n May. A decrease i n the midday s u r f a c e i r r a d i a n c e from 5.4 to 2.6 E i n s t e i n s / m^/hr due t o c l o u d cover r e s u l t e d i n the t r a n s f o r m a t i o n r a t e c o n s t a n t going from 1.07 t o 0.30 h r " . The decrease i n t r i c h l o r o p h e n o l p h o t o l y s i s was p r o p o r t i o n a l l y g r e a t e r than the decrease i n measured i r r a d i a n c e , t h i s may have been due t o c l o u d s a t t e n u a t i n g u l t r a v i o l e t - b l u e l i g h t more than v i s i b l e l i g h t s i n c e the r a d i o m e t e r o n l y measured r a d i a t i o n i n the v i s i b l e r e g i o n (400-700 nm). Maximum absorbance of t r i c h l o r o phenol was at 310 nm (Table I I ) . a

1


1

- 1

8

1

1

1



b

a

a

1.8

±0.3* 1.46 ± 0.09

1.57 ± 0.06

± 0.3

0.7 ± 0.1

0.6 ± 0.1

0.4 ± 0.1

D i s t i l l e d Water

Pentachlorophenol

a

- p K v a l u e s o f d i c h l o r o p h e n o l , t r i c h l o r o p h e n o l , and p e n t a c h l o r o p h e n o l a r e 7.6, 7.0, and 4.8, r e s p e c t i v e l y (Boule ^ t al., E r n s t and Wever, 1978). A s t e r i s k s (*) denote s i g n i f i c a n t d i f f e r e n c e s from the r a t e c o n s t a n t s o b t a i n e d a t pH 7.6 ( t - t e s t ; ρ £ 0.05). - pH of p h o s p h a t e - b u f f e r e d d i s t i l l e d water (0.017 M) or e s t u a r i n e water was a d j u s t e d u s i n g e i t h e r 2N NaOH or 2N H2SO4.

± 0.2*

1.4

pH 10

1.2

1.3 ± 0.2

1.00 ± 0.06

0.82 ± 0.06

0.40 ± 0.05*

0.13 ± 0.04*

0.13 ± 0.06*

pH 7.6

b

0.07 ± 0.06*

pH 5 . 5

E s t u a r i n e Water


E s t u a r i n e Water

A

2,4,5-Trichlorophenol F i r s t Order Rate Constant ( h r ~ )

i n Water


2,4-Dichlorophenol

Table I I I . E f f e c t o f pH on P h o t o l y s i s o f C h l o r o p h e n o l s


c/a

η •< 00 Η m

C

Ο Η Ο η a: m g c/5 H *> •< Ο "Π m < g ζ m ^ >

8

Table

IV. P h y s i c a l and Chemical P r o p e r t i e s of Skidaway R i v e r W a t e r , Physical


Temp (°C)

1

Z99(cm)

0

pH

0.22 ( O c t . 1983) 0.05 (Feb. 1984)

c

21 100

d

(K-Da ) (cm" ) 1

7.7 ± 0.2 (7.4-8.0)

Dissolved organic carbon (mg L " )

( O c t . 1983) ( F e b . 1984)

4.8 ± 0.3

1

P a r t i c u l a t e organic carbon (mg I T )

0.9 ± 0 . 1

P a r t i c u l a t e organic n i t r o g e n (mg I T )

0.20 ± 0.05

1

1

0.15 ( O c t . 1983) 0.01 ( F e b . 1984)

3 3 0

1983-1985

Chemical P r o p e r t i e s

Particulates 31.3 1 17.1 (12.9-68.3)

1

Kicm" )

Properties

21.7 ± 6.3 (7-29)

Suspended (mg L " )

C/N

4.6 ± 1 . 3

Phosphate a

37


3. HWANG ET AL.

(yg-atotn/L)

0.7 ± 0.3

0.05 ± 0.02 (0.030-0.096)

3 3 0

Nitrate 1

1

(ug-atom/L)

1.4 ± 0.3

3

K ( l mg" cm' )* 6.5 χ 1 0 " (Oct. 1983) s

0.6 χ Ι Ο "

3

(Feb. 1984) Salinity

0.85

(°/oo)

22.8 ± 2.4 (18-25)

± 0.04 (0.82-0.88)

a

-

E x p r e s s e d as the annual mean ± s t a n d a r d

b

«

Diffuse attenuation

coefficient.

c

*

Z99 - 4.6/K, p h o t i c

zone

d

«

Component o f Κ due t o l i g h t a t t e n u a t i o n by suspended p a r t i c u l a t e s . a o i the absorbance (1-cm p a t h l e n g t h ) o f the p a r t i c u l a t e - f r e e e s t u a r i n e water. D: d i s t r i b u t i o n c o e f f i c i e n t i n e s t u a r i n e water.

deviation

depth. 8

3 3

e

Photochemistry of Environmental Aquatic Systems - American

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