Factors Affecting the Distribution of H2O2 in Surface Waters

12 Factors Affecting the Distribution of H O in Surface Waters 2

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William J. Cooper , Chihwen Shao , David R. S. Lean , Andrew S. Gordon , and Frank E . Scully, Jr.

Downloaded by UNIV OF QUEENSLAND on April 26, 2016 | http://pubs.acs.org Publication Date: May 5, 1994 | doi: 10.1021/ba-1994-0237.ch012

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Drinking Water Research Center, Florida International University, Miami, FL 33199 National Water Research Institute, Burlington, Ontario L7R 4A6, Canada Department of Biological Sciences and Department of Chemical Sciences, Old Dominion University, Norfolk, VA 23529

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This chapter presents a review of the factors that affect both the formation and the decay of hydrogen peroxide, H O , in fresh waters. Although biological and chemical (nonphotochemical) processes form H O , their contribution to surface waters is generally insignificant. The formation of hydrogen peroxide results principally from the UV portion of sunlight exciting humic substances in the water and thereby leads to the formation of superoxide ion, which reacts with itself to form H O . Because this production is limited to the depth of UV light penetration, its vertical distribution provides a sensitive tracer for mixing processes. The known chemical pathways for the decay of H O appear to be insignificant in freshwater systems. Although some algae and zooplankton show catalase and peroxidase activity, the major organisms responsible for the decay of H O are heterotrophic bacteria. 2

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HYDROGEN PEROXIDE IN AQUEOUS SOLUTION

can act as e i t h e r an o x i d i z i n g or a r e d u c i n g agent (I ). T h e presence of h y d r o g e n p e r o x i d e has b e e n r e p o r t e d i n fresh waters (2-18), m a r i n e waters (19-25), a n d estuarine e n v i r o n m e n t s (26-28). H 0 affects redox c h e m i s t r y i n m a r i n e e n v i r o n m e n t s (15, 21, 24, 29-32) a n d m a y also b e i m p o r t a n t i n m e t a l c y c l i n g i n o t h e r natural waters (33-39) a n d i n t h e fate o f pollutants i n the e n v i r o n m e n t (7, 40-45). A s a strong oxidant, it m a y affect b o t h biological processes (46-48) a n d c h e m i c a l 2

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0065-2393/94/0237-0391$09.00/0 © 1994 American Chemical Society

Baker; Environmental Chemistry of Lakes and Reservoirs Advances in Chemistry; American Chemical Society: Washington, DC, 1994.

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ENVIRONMENTAL CHEMISTRY O F L A K E S A N D RESERVOIRS

processes a n d , as a result, m a y shape ecosystem b i o g e o c h e m i s t r y . T o u n derstand its d i s t r i b u t i o n i n natural waters, it is necessary to u n d e r s t a n d t h e mechanisms of H 0 formation a n d decay. 2

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T h e major i n situ process that results i n t h e formation o f H 0 is u n d o u b t e d l y p h o t o c h e m i c a l (e.g., 12, 15, 49, 50). P h o t o c h e m i c a l f o r m a t i o n o f H 0 i n fresh a n d salt waters p r o b a b l y results f r o m t h e d i s p r o p o r t i o n a t i o n of t h e superoxide i o n radical, 0 ~ (8, 9, 15, 5 1 , 52). T h e kinetics o f super oxide d i s p r o p o r t i o n a t i o n are w e l l established (53), a n d its steady-state c o n centration can b e calculated. Because o f the k n o w n effects o f superoxide i o n i n cells (47), its presence i n surface waters may b e i m p o r t a n t i n b i o l o g i c a l l y m e d i a t e d processes. H o w e v e r , other sources, such as b i o l o g i c a l f o r m a t i o n (e.g., 45, 54), redox c h e m i s t r y (21, 24, 29, 31, 32), w e t (e.g., 55) a n d d r y (50, 56, 57) d e p o s i t i o n , a n d surfaces (e.g., 58) m a y also b e i m p o r t a n t . 2

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Several studies o n t h e d e c o m p o s i t i o n o f H 0 i n natural waters strongly suggest that m i c r o b i o l o g i c a l processes play an i m p o r t a n t role (13, 14, 16, 45). T h e relative i m p o r t a n c e o f c h e m i c a l processes i n t h e d e c o m p o s i t i o n o f H 0 has not b e e n evaluated, b u t i t appears to b e s m a l l . A l t h o u g h early studies i n t h e m a r i n e e n v i r o n m e n t s h o w e d little d i e l v a r i a b i l i t y i n t h e surface-water H 0 concentration (22, 23), i n i t i a l obser vations o f rather h i g h concentrations o f H 0 i n surface waters o f lakes l e d us to examine t h e factors affecting its v a r i a b i l i t y a n d d i s t r i b u t i o n . T h i s chapter p r o v i d e s a c r i t i c a l r e v i e w o f t h e literature o n H 0 f o r m a t i o n a n d decay, integrated w i t h recent results o f b o t h f i e l d a n d laboratory studies. T h e f i e l d studies w i l l focus o n t h e f o r m a t i o n a n d d i s t r i b u t i o n o f H 0 i n a w i d e range o f lakes c o m p a r e d w i t h that o b t a i n e d i n an estuarine system, the C h e s a p e a k e B a y . L a b o r a t o r y studies o n t h e d e c o m p o s i t i o n o f H 0 i n natural waters, f i l t e r e d natural waters (using various size filters), a n d waters w i t h p u r e cultures o f two bacteria [Vibrio alginolyticus, a c o m m o n estuarine b a c t e r i u m (59, 60), a n d Enterobacter cloacae, a c o m m o n freshwater bac t e r i u m ] w i l l clarify t h e role o f bacteria i n t h e decay processes. 2

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Materiah and Methods H 0 Determination. T h e analytical m e t h o d f o r d e t e r m i n a t i o n o f H 0 measures t h e loss i n fluorescence o f scopoletin b y t h e peroxidasem e d i a t e d d e c o m p o s i t i o n of H 0 (11, 61-64). Separate standard curves w e r e d e t e r m i n e d for each water o r c u l t u r e s t u d i e d because t h e slope o f the c u r v e is affected b y d i s s o l v e d organic carbon (65, 66). 2

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Microbiological Studies. Bacterial n u m b e r s for t h e C h e s a p e a k e B a y samples a n d t h e p u r e cultures w e r e d e t e r m i n e d b y a c r i d i n e orange d i r e c t counts ( A O D C ) (67). Those for the lakes w e r e d e t e r m i n e d b y epifluorescence (68) u s i n g D A P I ( 4 ' , 6 - d i a m i d i n o - 2 - p h e n y l i n d o l e ) w i t h a final stain c o n c e n tration o f 1.0 μ g / m L , a process that is d e s c r i b e d i n d e t a i l elsewhere (69).


12.

COOPER ET AL.

Distribution

of H 0 2

in Surface Waters

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393

Bacterial cells f o r the laboratory studies w e r e p r e p a r e d b y g r o w i n g V. alginolyticus i n a M 9 m i n i m a l salts bacterial g r o w t h m e d i u m w i t h 8 m M glucose as the c a r b o n a n d e n e r g y source (70). T h e standard M 9 m e d i u m was m o d i f i e d b y a d d i t i o n o f 21 g / L o f N a C l ( S W M 9 ) . W a t e r u s e d for a l l studies was d e i o n i z e d a n d passed t h r o u g h a reverse osmosis m e m b r a n e ( M i l l i - Q ) . C e l l s w e r e transferred f r o m an o v e r n i g h t l i q u i d c u l t u r e to fresh m e d i u m a n d g r o w n o v e r n i g h t (~18 h) o n a gyrorotary shaker at r o o m t e m p e r a t u r e . T h e cells w e r e harvested b y centrifugation (11,000 g , 10 min) a n d resusp e n d e d i n sterile assay buffer (0.01 M phosphate buffer, N a salt, 0.26 M N a C l , p H 6.78; the p H p r i o r to sterilization was 7.20). T h e c e l l c o n c e n t r a t i o n was adjusted to a p p r o x i m a t e l y 5 X 1 0 / m L as j u d g e d b y o p t i c a l d e n s i t y o f the s o l u t i o n . T h e actual n u m b e r s i n d i l u t i o n s o f the c e l l suspensions w e r e d e t e r m i n e d b y d i r e c t counts. E. cloacae was g r o w n as d e s c r i b e d , except that the M 9 c o n t a i n e d 0.5 g / L o f N a C l .


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H 0 Formation Studies. F o r m a t i o n rates at specific depths o r at the surface w e r e d e t e r m i n e d b y u s i n g quartz glass tubes w i t h q u a r t z glass stoppers. T h e tubes w e r e f i l l e d w i t h t h e selected waters a n d p l a c e d at t h e surface o r at p r e d e t e r m i n e d depths i n t h e w a t e r c o l u m n . P l a c i n g t h e glass tubes i n t h e a m b i e n t water e n s u r e d that a constant t e m p e r a t u r e was m a i n t a i n e d a n d m i n i m i z e d the tube w a l l effects. I n a l l samples a n i n i t i a l H 0 concentration was d e t e r m i n e d . T h e samples w e r e t h e n exposed to s u n l i g h t for 1 h , after w h i c h t h e H 0 concentration was again d e t e r m i n e d . T h e f o r m a t i o n rate (per hour) was calculated b y subtracting t h e i n i t i a l c o n c e n tration f r o m the final H 0 concentration. 2

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H 0 Decay Studies. U n f i l t e r e d lake waters w e r e stored i n w a s h e d 2 - L p o l y e t h y l e n e bottles i n the dark, a n d t h e H 0 concentrations w e r e m e a s u r e d at specified intervals. L a k e waters w e r e f i l t e r e d t h r o u g h 0.2-, 1.0-, 5.0-, a n d 12.0-μπι microfilters (Nuclepore). Z o o p l a n k t o n w e r e r e m o v e d w i t h 30-μπι w o v e n n y l o n (Nitex) screens. G e n e r a l l y 1 L of filtrate was u s e d . Samples for d e t e r m i n i n g decay rates o f H 0 i n C h e s a p e a k e B a y water w e r e m a i n t a i n e d as close to a m b i e n t water t e m p e r a t u r e as possible. T h e decay studies w e r e c o n d u c t e d i n 1 - L glass bottles m a i n t a i n e d i n t h e dark w i t h o u t shaking. 2

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T h e studies o n p u r e cultures w e r e c o n d u c t e d at 25 °C i n the laboratory. Chesapeake B a y water samples w e r e f i l t e r e d t h r o u g h the f o l l o w i n g filters: 0 . 1 - μ η ι T u f f r y n M e m b r a n e , H T 1 0 0 (Gelman); 0 . 2 2 - μ π ι M P G L 06S H 2 ( M i l lipore); a n d 0.45-μΐΏ G N - 6 (Gelman). Sample Collection. W a t e r samples f r o m t h e lakes a n d t h e C h e s a peake B a y w e r e o b t a i n e d f r o m either standard 6 - L N i s k i n sample bottles o r a p u m p i n g system e m p l o y e d to collect samples for rare earth elements (71).


394


Irradiation Measurements. A n E p p l y p h o t o m e t e r w i t h sensors for total global irradiance, photosynthetic active radiation ( P A R ) , a n d u l t r a v i o l e t ( U V ) radiation ( 2 9 5 - 3 8 5 nm) was u s e d to measure irradiance c o n t i n u o u s l y and averaged a m e a s u r e m e n t e v e r y 0 . 5 h .


Study Areas T h e studies r e p o r t e d h e r e w e r e c o n d u c t e d i n several different e n v i r o n m e n t s . T h e lakes s t u d i e d i n c l u d e d L a k e E r i e , L a k e O n t a r i o ( H a m i l t o n H a r b o r at the e x t r e m e w e s t e r l y e n d o f L a k e Ontario), a n d Jacks L a k e a n d R i c e L a k e i n O n t a r i o , C a n a d a . T h e locations of the stations a n d study areas are s h o w n i n F i g u r e 1; m o r e details are d e s c r i b e d elsewhere (13, 14). T h e study sites i n t h e Chesapeake B a y are s h o w n i n F i g u r e 2. D e p t h profiles w e r e o b t a i n e d at b o t h t h e N o r t h a n d S o u t h B a s i n locations, w h e r e the w a t e r c o l u m n was oxic t h r o u g h o u t a n d h a d a fairly constant 0 c o n c e n tration o f 5 m g / L . T h e surface-water t e m p e r a t u r e , a p p r o x i m a t e l y 10 ° C , r e m a i n e d constant at t h e S o u t h B a s i n t h r o u g h o u t t h e w a t e r c o l u m n w h i l e decreasing i n t h e N o r t h B a s i n to slightly less than 9 ° C i n t h e l o w e r 18 m of the water c o l u m n . A t b o t h locations t h e surface water (approximately t h e top 10 m) was r e l a t i v e l y fresh, w i t h a saltwater w e d g e at t h e b o t t o m . T h e surface-water salinity increased f r o m t h e N o r t h B a s i n (10.6% ) to t h e S o u t h B a s i n (12.3%). 2

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Bancroft

Figure 1. Lake study areas and sampling locations.


Distribution

of H 0 2

2

in Surface Waters


COOPER ET AL.

Figure 2. Sampling locations in the Chesapeake Bay.


396


T h e transect began i n t h e u p p e r reaches o f t h e b a y i n w a t e r that h a d a surface salinity o f 0.21%> a n d p r o c e e d e d i n a s o u t h e r l y d i r e c t i o n w i t h sam p l i n g at five locations, T 1 - T 5 , w h e r e the salinity was 7.9%>. T h e d a y o f t h e transect, A p r i l 13, 1988, was clear a n d s u n n y , w i t h w i n d s o f 1 8 - 2 5 knots.

Results and Discussion D e t a i l e d studies o f H 0 d i s t r i b u t i o n i n m a r i n e systems a n d factors affecting its f o r m a t i o n have r e s u l t e d p r i m a r i l y f r o m the w o r k o f Z i k a a n d co-workers (9, 11, 12, 20-24, 30, 31). T h e s e studies i n d i c a t e d that t h e surface ocean, 5 m a n d less d e e p , was close to 100 n M i n H 0 . S o m e d i e l v a r i a b i l i t y was r e p o r t e d i n subtropical surface waters, b u t the variation f r o m n i g h t to d a y was a p p r o x i m a t e l y 1 0 - 2 0 % . I n i t i a l studies o f Jacks L a k e , O n t a r i o , C a n a d a (13), s h o w e d surface water (1 m a n d less) d i e l v a r i a b i l i t y o f f r o m < 1 0 n M at n i g h t to > 5 0 0 n M d u r i n g t h e day. T h e contrasting d i e l p a t t e r n o b s e r v e d i n t h e t w o systems l e d us to the next phase o f o u r e x p e r i m e n t s . 2

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W e d e t e r m i n e d the net f o r m a t i o n rates i n discrete samples at several depths i n the water c o l u m n , w i t h a n d w i t h o u t f i l t r a t i o n , u s i n g waters f r o m several lakes. W e also investigated the decay processes, i n the dark, for w h o l e lake waters, lake waters filtered t h r o u g h v a r y i n g m e s h size filters, a n d i n p u r e bacterial cultures. T h e s e results a d d e d to o u r u n d e r s t a n d i n g o f the processes responsible for the o b s e r v e d d i s t r i b u t i o n o f H 0 . O u r c u r r e n t research activities (18) are r e v i e w e d a n d s y n t h e s i z e d i n this chapter. 2

Formation of

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H0 2

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Photochemical Formation. T h e major pathway l e a d i n g to t h e for m a t i o n o f H 0 i n surface waters (fresh a n d marine) results f r o m p h o t o c h e m i c a l l y (sunlight) m e d i a t e d reactions o f d i s s o l v e d organic c a r b o n (e.g., 12, 15). T h e p o r t i o n o f the sunlight most responsible for the f o r m a t i o n o f H 0 is that p o r t i o n b e l o w 400 n m . T h e i n t e r m e d i a t e i n t h e process appears to b e 0 * ~ (8, 9, 12, 15, 51, 52, 72). T h u s , those reactions that l e a d to t h e formation o f 0 *~ i n natural waters w i l l increase t h e f o r m a t i o n o f H 0 , a n d those that lead to the loss o f 0 *~ w i l l result i n l o w e r concentrations o f H 0 i n natural waters. T h e f o l l o w i n g g e n e r a l i z e d reaction m e c h a n i s m has b e e n p r o p o s e d (12, 15): 2

2

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JDOC - ^ t }DOC* i 1 D O C * or f D O C * [DOC 0

+

2

+ e~] + e " a q

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>[DOC >DOC*

+

+

?DOC*

2

(1)

+ e ]

(2)

+ e "

(3)

a q

> ΟΓ


(4)

12.

COOPER ET AL.

Distribution

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0

2

» DOC

fDOC* +

3

0

2

> èDOC + 0

l

fDOC* + RNH

+

+ 0 -

>DOC*

+

(6)

2

+ 0 -

(7)

2

2

>D O C " + RNH

+ 0

2

> IOOC

JDOC + Ό

2

» endoperoxides

DOC"

(5)

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l

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397

in Surface Waters

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?DOC* +

iDOC + 0


of H 0

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(8)

+

+ 0 -

(9)

2

>DOC + H 0 2

2

(10)

w h e r e D O C is the sunlight-absorbing d i s s o l v e d organic c a r b o n , ( / D O C is the g e n e r a l i z e d electronic g r o u n d state, ^ D O C * is t h e g e n e r a l i z e d elec tronically excited singlet state, j D O C * is t h e g e n e r a l i z e d e l e c t r o n i c a l l y ex c i t e d t r i p l e t state, a n d I S C is intersystem crossing. T h e equations suggest that the rate o f formation s h o u l d b e related to the concentration o f d i s s o l v e d organic carbon. T h i s relationship has b e e n d e m o n s t r a t e d (12, 15, 18), a l t h o u g h natural v a r i a b i l i t y does exist. T h e s e results have b e e n e x t e n d e d to several natural waters obtained f r o m various temperate lakes a n d t h e G r e a t L a k e s . D a t a for net formation rates o f H 0 at t h e surface are s u m m a r i z e d i n Table I, b u t i n each e x p e r i m e n t i n c i d e n t a l l i g h t was not c o n t r o l l e d . I n c i d e n t a l l i g h t varies w i t h latitude, season, a n d c l o u d cover. In earlier studies i t was p r e s u m e d that filtration w o u l d not significantly affect formation rates because major decay processes w e r e p r e s u m e d to b e c h e m i c a l l y m e d i a t e d (11,12). Therefore little attention was g i v e n to f i l t e r e d versus u n f i l t e r e d formation rates. H o w e v e r , w e have s h o w n that m i c r o b i a l processes are i m p o r t a n t (16). Therefore, the formation rate of H 0 i n b o t h filtered (0.2-μιη) a n d u n f i l t e r e d (whole) lake water was d e t e r m i n e d i n this study. I n most o f the samples the formation rate o f t h e f i l t e r e d w a t e r was h i g h e r than that o f the w h o l e (unfiltered) lake water, a result i n d i c a t i n g that p a r t i c l e - m e d i a t e d (biological) decay processes are i m p o r t a n t o n 1-h t i m e scales. Q u a n t u m y i e l d s (reflecting the efficiency o f c o n v e r t i n g sunlight e n e r g y to t h e formation o f H 0 at several wavelengths) i n natural waters ( F i g u r e 3) suggest that i n h i g h - h u m i c waters most o f the H 0 f o r m a t i o n w i l l o c c u r i n the near-surface water (11, 12). That is, the q u a n t u m y i e l d s are highest at the l o w wavelengths that are absorbed i n the waters near t h e surface. F i g u r e 4 shows t h e H 0 formation rate variation w i t h d e p t h (up to 1 m) i n Sharpes B a y ( D O C = 5 . 7 m g / L , w i t h filtered water). T h e rate was deter m i n e d b y i n c u b a t i n g the sample for 1 h at a n integrated solar U V i r r a d i a t i o n of 3.02 L a n g l e y s . T h e formation rate at d e p t h is c o n s i d e r a b l y slower than at t h e surface. T h e effect of c l o u d cover o n t h e formation of H 0 was established d u r i n g a d i e l study o f H 0 i n surface waters (13). H o w e v e r , the effect o f d e p t h o n the formation rate has not b e e n r e p o r t e d . F i g u r e 4 shows that o n a hazy 3

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Table I. H 0 Formation Rate at the Surface i n Natural Waters Under Natural Sunlight Conditions 2

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Water

Weather

Sample Condition'

DOC (mgih)

Formation Rate (nM/h)

Un F F F Un F F Un

6 ± 0.5 5.7

120-360 126-221 44 310-350 373 102 218 202

F Un

4.2

Jacks Lake Sharpes Bay


Brooks Bay Hamilton Harbor

sunny cloudy sunny sunny cloudy

Lake Erie Station 23 Lake Ontario Station 41

1

F Un F Un F Un

Station 212 Rice Lake Greifensee Glatt Zurichsee Etang de la Gruere

7.2

4.1

3.4 7.9 4-4.5 -4.5 1.5 13

51 29 70 51 43 31 526 451 160-300 180 -30 1000

Réf.

this this this this this this this

13 study study study study study study study

this study this study this this this this this this

study study study study study study 15 15 15 15

"Un is unfiltered; F is filtered (0.2-μηι filter).

Ο SPRING WATER Δ WELL WATER • LAKE WATER

0.002 9 ill

I i

0.001 ι

ζ Lu CL
2H 0 + 0 2

2

(13)

2


and for peroxidase: peroxidase + H 0 2

2

> perox I

(14) (15)

perox I + A H

2

> perox II + A H -

perox II + A H

2

> peroxidase + A H - + H 0

(16)

2

w h e r e perox I a n d II are " a c t i v a t e d " peroxidase states a n d A H is a gener2

alized hydrogen donor. T h e s e e n z y m e systems are w i d e s p r e a d i n nature (90, 91). S e v e r a l lines of investigation have l e d to the c o n c l u s i o n that these processes may account for most b i o l o g i c a l l y m e d i a t e d decay of H 0 o b s e r v e d i n natural waters. 2

2

Enzyme Decay. M o f f e t t a n d Z a f i r i o u (I) differentiated catalase- a n d p e r o x i d a s e - m e d i a t e d decay i n coastal (marine) waters b y u s i n g O - l a b e l e d H 0 a n d 0 , a n d b y d e t e r m i n i n g the l a b e l e d e n d p r o d u c t s . E q u a t i o n 13 shows that the products of catalase d e c o m p o s i t i o n are H 0 a n d 0 . I n c o n trast, peroxidase d e c o m p o s i t i o n results i n the f o r m a t i o n of H 0 w i t h o u t 0 . F r o m the m e a s u r e m e n t of the relative a m o u n t of l a b e l e d p r o d u c t s it is possible to d e t e r m i n e the c o n t r i b u t i o n of b o t h e n z y m e s i n the decay of the H 0 . I n the coastal water, 6 5 - 8 0 % of the d e c o m p o s i t i o n was a t t r i b u t e d to catalase a n d the rest to peroxidase (I). T h e s e studies are the first to use this t e c h n i q u e . T h e approach s h o u l d be e x t e n d e d to freshwater ecosystems to see i f the same pattern w o u l d be f o u n d . l s

2

2

2

2

2

2

2

2

2

A n o t h e r approach uses the c o u p l i n g reaction of p - a n i s i d i n e . I n the presence of H 0 a n d peroxidase (16), an oxidation p r o d u c t that contains t w o aromatic rings, b e n z o q u i n o n e - 4 - m e t h o x y a n i l i n e , is f o r m e d s t o i c h i o m e t r i cally (92). E q u a t i o n s 1 4 - 1 6 indicate that an e l e c t r o n d o n o r or h y d r o g e n d o n o r is r e q u i r e d for p e r o x i d a s e - m e d i a t e d d e c o m p o s i t i o n o f H 0 . I n t w o natural waters a n d one soil suspension, peroxidatic activity was i d e n t i f i e d b y the s t o i c h i o m e t r i c r e m o v a l of p - a n i s i d i n e b y the a d d i t i o n o f H 0 (in the dark) (16). T h i s p r o c e d u r e p r o v i d e s an i n d e p e n d e n t c o r r o b o r a t i o n of the results o b t a i n e d b y M o f f e t t a n d Z a f i r i o u (J). H o w e v e r , this m e t h o d does not quantify the relative i m p o r t a n c e of peroxidases versus catalases i n the d e c o m p o s i t i o n of H 0 . 2

2

2

2

2

2

2


2

12.

COOPER ET AL.

Distribution

of H 0 2

2

403

in Surface Waters

F i l t r a t i o n S t u d i e s . W e e x a m i n e d b i o l o g i c a l l y m e d i a t e d decay o f H 0 by m e a s u r i n g decay rates o n lake waters filtered t h r o u g h filters w i t h various m e s h sizes. T h e filters u s e d w e r e 64 μπι to r e m o v e z o o p l a n k t o n , 12 μηι to r e m o v e large algae, 1.0 μπι to r e m o v e s m a l l algae, a n d 0.2 μηι to r e m o v e bacteria. E x a m p l e s of the effect of filtration o n the decay rate o f H 0 i n natural waters are s h o w n i n Table II, a n d a d d i t i o n a l data are p r o v i d e d b y L e a n et a l . (28). A p p a r e n t l y r e m o v a l o f the z o o p l a n k t o n a n d large algae causes little difference i n H 0 decay. H o w e v e r , w h e n smaller particles (small algae a n d bacteria) are r e m o v e d , H 0 b e c o m e s q u i t e stable i n the water. T h e s e observations are consistent w i t h data o b t a i n e d (93) w h e n i n h i b i t o r s of m i c r o b i a l activity w e r e a d d e d to solutions of s u s p e n d e d sediments a n d natural waters. W h e n f o r m a l d e h y d e o r Hg(II) was a d d e d , the H 0 was stable a n d no decay o c c u r r e d . I n other w o r d s , decay is r e l a t e d to particles i n the water. T h e s e particles are l i k e l y to b e s m a l l p l a n k t o n a n d bacteria. 2

2

2

2

2

2


2

2

2

2

P u r e C u l t u r e Studies. T w o bacteria w e r e c u l t u r e d to s t u d y the d e c o m p o s i t i o n of H 0 , Vibrio alginolyticus a n d Enterobacter cloacae. V. alginolyticus was selected because it is an e x t r e m e l y c o m m o n inhabitant of e n v i r o n m e n t s l i k e the C h e s a p e a k e B a y . V i b r i o s m a y p r o v i d e u p to 5 0 % of the c u l t u r a b l e bacterial species i n the bay (60). E. cloacae was s t u d i e d because it is c o m m o n l y f o u n d i n freshwater e n v i r o n m e n t s (94). D e c a y studies u s i n g V. alginolyticus w e r e c o n d u c t e d at a constant H 0 concentration as a f u n c t i o n of c e l l concentration, a n d at a constant c e l l c o n centration as a f u n c t i o n of H 0 concentration. T h e five c e l l concentrations represent various e n v i r o n m e n t s , f r o m h i g h l y p r o d u c t i v e areas to o l i g o t r o p h i c waters, 10 to 10 c e l l s / m L , respectively. T r i p l i c a t e e x p e r i m e n t s w e r e c o n d u c t e d at each c e l l concentration, a n d the c o m b i n e d results are s u m m a r i z e d i n T a b l e III. A t each c e l l concentration of V. alginolyticus the rate of d e c o m p o s i t i o n t h r o u g h the first one o r two half-lives was o b t a i n e d b y least2

2

2

2

7

2

2

5

Table II. The Loss of H 0 i n Sharpes Bay (Jacks Lake) Water and Filtrates of Lake Water 2

2

Lake Water

Sharpes Bay Vertical Profile

Filter Size

Organisrns

tin (h)

Depth (m)

Unfiltered 64 μηι 12 μηι 1.0 μιτι 0.2 μηι

Natural assemblage Zooplankton removed Large algae removed Small algae removed Bacteria removed

4.4 4.7 6.4 19.1 58.7

Surface 1 2 3 4 5 6

Rate Constant (h~*) 0.122 0.119 0.120 0.130 0.110 0.124 0.115

tj/i (h) 5.7 5.8 5.8 5.3 6.3 5.5 6.0

N O T E : The half-life (f ) was determined at 20 ° C as it would be for a first-order kinetic process (i.e., the In 2 divided by the decay rate constant). 1/2


404


Table III. Hydrogen Peroxide Decomposition by a Marine Bacterium Vibrio alginolyticus Culture (H Oj


2

0

(nM)

Rate Constant (min *)

2175 1120 1052 530 540 114 108 31.9 28.9

tl/2 (h) 0.79 0.72 0.78 0.64 0.67 0.35 0.42 0.39 0.69

-0.015 -0.016 -0.015 -0.018 -0.017 -0.033 -0.028 -0.030 -0.017

Cells! mL(x 14 7 1.4 0.7 0.14

10 ) 6

0.49 1.08 2.67 15.8 37.3

-0.024 -0.011 -0.0043 -0.00073 -0.00031

N O T E ; In the experiments with varying [H 0 ], the V. alginolyticus concentration was 1.4 Χ 10 cells/mL. In the experiments with varying cell concentration, the [H 0 ] was 132 nM. The culture medium was 0.01 M phosphate, pH 6.78, containing 15 g/L of NaCl and kept at 25 °C. 2

2

7

2

2

squares regression analysis at t i m e t of In ( [ H 0 ] ) . T h e decay rate constants are also s u m m a r i z e d i n T a b l e III. 2

2

t

A t a c e l l concentration of 1.4 Χ 10 c e l l s / m L , the H 0 decay rate was m e a s u r e d w i t h i n the [ H O ] range f r o m 28.9 to 2175 n M . T h i s range brackets surface water concentrations f o u n d i n various e n v i r o n m e n t s , a l t h o u g h the highest H 0 concentrations s t u d i e d have n e v e r b e e n o b s e r v e d i n n a t u r a l waters. A decrease i n decay rate was o b s e r v e d at h i g h e r H 0 concentrations. T h i s decrease is p r o b a b l y caused b y some i n h i b i t i o n of the organisms at h i g h H 0 concentrations. 7

2

2

2

2

2

0

2

2

2

2

2

S e v e r a l e x p e r i m e n t s , u s i n g solutions o f H 0 to w h i c h organisms h a d b e e n a d d e d , w e r e a l l o w e d to c o n t i n u e u n t i l no f u r t h e r d e c o m p o s i t i o n was o b s e r v e d . I n e v e r y case the H 0 concentration was 2 - 5 n M . T o d e t e r m i n e w h e t h e r this result was an artifact of the analytical m e t h o d , excess catalase was a d d e d to several solutions a n d H 0 was m e a s u r e d after several h o u r s . I n a l l cases i n w h i c h excess catalase h a d b e e n a d d e d , the H 0 c o n c e n t r a t i o n was r e d u c e d to b e l o w the detection l i m i t , 1 n M . T h i s l o w e r l i m i t for H 0 concentration m a y indicate b i o l o g i c a l f o r m a t i o n o f H 0 , as suggested b y P a l e n i k (87, 88). F u r t h e r studies are r e q u i r e d to d e t e r m i n e the reason for the l o w steady-state concentrations o f H 0 i n the c u l t u r e s . 2

2

2

2

2

2

2

2

2

2

2

2

2


2

12.

COOPER ET AL.

Distribution

of H 0 2

in Surface Waters

2

405

H 0 decay i n p u r e cultures o f V. alginolyticus was s h o w n to b e second o r d e r o v e r a l l a n d first o r d e r i n [ H 0 ] a n d c e l l c o n c e n t r a t i o n , as s h o w n b y e q 17: 2

2

2

-d[H 0 ] 2

2

2

=

fcbajH202][cells]

(

1

7

)

dt w h e r e fc is the second-order rate constant for a specific b a c t e r i u m , a n d [cells] is i n organisms p e r m i l l i l i t e r . baot

F o r V. alginolyticus at 132 n M H 0 a n d v a r y i n g b a c t e r i a l c e l l c o n c e n tration, t h e second-order rate constant was: Downloaded by UNIV OF QUEENSLAND on April 26, 2016 | http://pubs.acs.org Publication Date: May 5, 1994 | doi: 10.1021/ba-1994-0237.ch012

2

fc

Va

2

= 2.3 Χ 1 0 " m L / c e l l s - m i n

(18)

9

S i m i l a r studies c a r r i e d out u s i n g E. cloacae s h o w e d that decay was s l o w e r at t h e h i g h e r concentrations o f H 0 than at t h e l o w e r concentrations (Table IV). H o w e v e r , t h e r e l a t i v e l y h i g h concentration o f H 0 m a y have i n h i b i t e d m i c r o b i a l activity. A t other concentrations t h e decay rate s e e m e d to b e firsto r d e r i n H 0 concentration a n d first-order i n c o n c e n t r a t i o n o f organisms, g i v i n g an o v e r a l l rate constant at 25 ° C : 2

2

2

2

2

2

k

Ec

= 5.1 X 1 0 ~ m L / c e l l s - m i n

(19)

9

T h u s , b o t h p u r e cultures w e r e efficient i n r e m o v i n g H 0 2

2

from solution and

the o v e r a l l rate constants w e r e v e i y s i m i l a r . Table IV. Hydrogen Peroxide Decomposition by a Freshwater Bacterium Enterobacter cloacae Culture [HiOJ.

(nM)

Rate Constant (min *)

ti/2 (h)

-0.00781 -0.00962 -0.0110

1.5 1.2 1.1 0.53 0.59

1726 1176 558 121 17.5

Cells/mL

-0.0218 -0.0196

(Χ 10 ) 6

10 5 1 0.5 0.1

0.23 0.40 2.59 15.4 30.4

-0.0499 -0.0290 -0.00446 -0.00075 -0.00038

N O T E : In the experiments with varying [H 0 ], the V. alginolyticus concentration was 1.4 X 10 cells/mL. In the experiments with varying cell concentration, the [H 0 ] was 132 n M . The culture medium was 0.01 M phosphate, p H 6.8, containing 15 g/L of NaCl and kept at 25 °C. 2

2

7

2

2


406


Several experiments w e r e c o n d u c t e d to characterize t h e H 0 decay i n the cultures a n d m e d i a . T h e s e experiments w e r e a l l c o n d u c t e d at H 0 concentrations l i k e l y to b e f o u n d i n natural waters. F i r s t , to test t h e p a r t i c l e associated d e c o m p o s i t i o n o f H 0 , V. alginolyticus was c u l t u r e d , c e n t r i f u g e d , and r e s u s p e n d e d i n fresh m e d i a . A p o r t i o n o f this r e s u s p e n d e d c u l t u r e was w i t h d r a w n , c e n t r i f u g e d , a n d filtered t h r o u g h a 0. l - μ η ι filter. T h e cell-free filtrate (from a c e l l suspension that was 5 . 6 X 10 c e l l s / m L ) was d i l u t e d to give an e q u i v a l e n t o f 1.4 X 1 0 c e l l s / m L at 126 n M H O . T h e c e l l suspension that h a d not b e e n filtered was also d i l u t e d i n t h e same s t e r i l i z e d m e d i u m to give a c e l l concentration o f 1.4 X 1 0 c e l l s / m L . T h e H 0 d e c o m p o s i t i o n rate constant for t h e l i v i n g cells was - 0 . 0 3 9 2 c e l l / m i n , w i t h a half-life o f 17.7 m i n (Table III). T h e filtrate s h o w e d n o loss o f H 0 d u r i n g a 5 0 - h p e r i o d . T h i s result establishes that the processes for t h e d e c o m p o s i t i o n o f H 0 i n these p u r e cultures is associated w i t h t h e l i v i n g organism a n d is n o t associated w i t h extracellular e n z y m e s o r metabolites. 2

2

2

2

2

2

8

7

2


7

2

a

2

2

2

2

2

S e c o n d , cultures o f V. alginolyticus w e r e heated i n a n i n c u b a t o r for 4 5 m i n at 62 ° C . T h i s relatively m i l d treatment w o u l d result i n a m i n i m u m change to n o n c e l l u l a r organic a n d inorganic c o m p o u n d s that m a y b e r e sponsible for H 0 d e c o m p o s i t i o n . A n aliquot (1 m L ) p l a t e d onto t r y p t i c soy agar (Difco) s h o w e d n o g r o w t h . T h e c e l l suspension was viscous after h e a t i n g , a result that i n d i c a t e d that c e l l lysis p r o b a b l y h a d o c c u r r e d . T h e h e a t - k i l l e d c e l l suspension was d i l u t e d i n s t e r i l i z e d m e d i u m , 126 n M H 0 , to a n e q u i v alent o f 1 0 c e l l s / m L . N o d e c o m p o s i t i o n o f H 0 was o b s e r v e d o v e r 50 h . T h i r d , azide i o n was a d d e d to d e t e r m i n e t h e effect o f this i n h i b i t o r . T h e respiration rate o f V. alginolyticus is s l o w e d b y t h e a d d i t i o n o f 10 m M azide i o n (92). O u r studies suggest that the a d d i t i o n o f azide i o n i n h i b i t s most o r all o f the d e c o m p o s i t i o n o f H 0 i n some natural waters and/or soil suspen sions (16). T h e r e f o r e , solutions o f H 0 w e r e p r e p a r e d i n s t e r i l i z e d m e d i u m . I n o n e flask o n l y N a N (10 m M ) was a d d e d . T o t h e other t w o flasks, 1.4 X 10 c e l l s / m L of V. alginolyticus w e r e a d d e d . A f t e r t h e d e c o m p o s i t i o n o f H 0 e q u i v a l e n t to one half-life, N a N (10 m M ) was a d d e d to o n e o f these flasks. I n t h e flask to w h i c h n o bacteria w e r e a d d e d , n o d e c o m p o s i t i o n o f the H 0 o c c u r r e d over 4 h . T h e rate o f H 0 d e c o m p o s i t i o n i n t h e p r e s e n c e o f 1.4 X 1 0 c e l l s / m L was - 0 . 0 3 9 2 c e l l / m i n , a n d n o change i n t h e rate o f d e c o m position was o b s e r v e d after t h e a d d i t i o n o f azide i o n . T h i s result indicates that for these laboratory cultures N " d i d not noticeably affect t h e m e c h a n i s m responsible for t h e decay o f H 0 . 2

2

2

7

2

2

2

2

2

2

2

3

7

2

2

2

2

3

2

2

7

3

2

2

Field Studies. E x p e r i m e n t s c o n d u c t e d at Jacks L a k e (13), L a k e E r i e a n d L a k e O n t a r i o (14,18), a n d u n d e r laboratory conditions u s i n g s u s p e n d e d sediments a n d natural waters (16,17) have a l l i m p l i c a t e d b i o l o g i c a l processes i n H 0 decay. U n f i l t e r e d Jacks L a k e w a t e r (Sharpes Bay) h a d a half-life (t ) for H 0 o f 7.8 h . F i l t r a t e f r o m 64-, 12-, a n d 5 - μ ι η filters w e r e a l l similar, w i t h an average t o f 8.6 h . T h e filtrate o f l - μ η ι filtration h a d 2

m

2

2

2

m


12.

COOPER ET AL.

Distribution

of H 0 2

2

407

in Surface Waters

a t o f 31 h , a n d t h e filtrate o f a 0 . 4 5 - μ η ι filter s h o w e d n o decay i n 24 h (13). m

T o d e t e r m i n e the H 0 decay rate correlated w i t h d e p t h , t w o locations w e r e s t u d i e d : station 212 i n L a k e O n t a r i o a n d Station 23 i n L a k e E r i e . A t b o t h s a m p l i n g locations t h e rate decreased w i t h d e p t h (i.e., t h e H 0 halflife increased. F o r example, at station 212, t h e t i n c r e a s e d f r o m 14.7 h i n the surface-water sample to 2 1 . 6 h i n t h e sample o b t a i n e d at 10 m . A t station 23 t h e surface t was 9.6 h , a n d it increased to 2 0 . 2 h i n t h e sample f r o m a w a t e r d e p t h o f 16.4 m . 2

2

2

2

m

m

A s u m m a r y o f o u r most recent studies o n b i o l o g i c a l l y m e d i a t e d decay is s h o w n i n F i g u r e 5. I n situ H 0 decay was d e t e r m i n e d b y u s i n g the natural l o g a r i t h m of the n i g h t t i m e areal concentration p l o t t e d versus t i m e . T h e decay rate constant was taken as t h e slope o f t h e l i n e . D e c a y rate constants c a l c u l a t e d u s i n g i n situ values w e r e s i m i l a r to w a t e r samples i n c u b a t e d i n bottles k e p t i n t h e dark i n t h e laboratory. T h e decay rate constants s e e m e d to correlate w i t h bacteria n u m b e r s . T h e t e m p e r a t u r e effect o n t h e decay rate o f H 0 i n u n f i l t e r e d Sharpes B a y water was d e t e r m i n e d b y a l l o w i n g samples to e q u i l i b r a t e at several temperatures ( F i g u r e 6). H 0 was s p i k e d i n a l l samples, a n d t h e decay was f o l l o w e d for several half-lives. W i t h l o w e r water temperatures t h e decay rate constants w e r e l o w e r . A s y e t this has not b e e n v e r i f i e d o v e r a season. A s w a t e r temperatures change t h e relationship m a y differ f o r cold-tolerant species. H 0 decay studies have also b e e n c o n d u c t e d i n waters f r o m t h e


2

2

2

2

2

2

2

2

0.15

ω ζ Ο Ο LU

Ο

BOTTLES

A

IN SITU

WEST Ο Stn 357ff SHARPES Ο (Sept.)

0.10

CHESAPEAKE BAY

CENTRAL Q Stn 84 w

SHARPES

(June)

Γ£ 0.05 ϋ LU Ο

EAST Stn 23

0.00 6

1

BACTERIA NUMBERS (X 10 mL" ) Figure 5. Hydrogen peroxide decay rate constants in surface-water samples from Sharpes Bay (in June and September), Jacks Lake, Ontario, Canada, from the East (Station 23), Central (Station 84), and West Basin (Station 357) of Lake Erie and the Chesapeake Bay, plotted as a function of bacteria numbers.


408



0.25

TEMPERATURE (°C) Figure 6. Decay rate constants for H 0 in unfiltered Sharpes Bay lake water contained in glass bottles in the dark at temperatures from 3 to 35 °C. Initial concentrations were about 270 nM. (Reproduced with permission from reference 17, Copyright 1990 Academic Press.) 2

2

u p p e r reaches o f t h e C h e s a p e a k e B a y . D e c a y studies w e r e p e r f o r m e d o n two d e p t h profiles a n d for surface samples starting i n t h e u p p e r B a y a n d p r o c e e d i n g south ( F i g u r e 2). Table V s u m m a r i z e s t h e h y d r o g e n p e r o x i d e concentration w i t h d e p t h , the decay rate constants o b t a i n e d for t h e N o r t h a n d S o u t h Basins, a n d t h e bacterial c e l l counts ( A O D C ) . B o t h stations w e r e s a m p l e d o n c l o u d y days, A p r i l 12, 1988, a n d A p r i l 14, 1988, N o r t h a n d S o u t h B a s i n , respectively. Because o f t h e l o w a m b i e n t concentrations o f H 0 , it was necessary to a d d H 0 p r i o r to m e a s u r i n g t h e decrease i n c o n c e n t r a t i o n w i t h t i m e . A t b o t h stations decay rates w e r e slower i n surface w a t e r t h a n i n d e e p e r water, a t r e n d opposite to that o b s e r v e d i n t h e samples o b t a i n e d f r o m L a k e O n t a r i o a n d L a k e E r i e . A l l o f the decay rates o b t a i n e d are c o m parable to, o r faster t h a n , those o b t a i n e d i n o t h e r coastal (estuarine) e n v i r o n m e n t s (W. J . C o o p e r , u n p u b l i s h e d data) a n d c o m p a r a b l e to those f o u n d i n some o f the freshwater lakes s a m p l e d . 2

2

2

2

T a b l e V I s u m m a r i z e s t h e s a m p l i n g location a n d t i m e , surface-water sal i n i t y , t h e m e a s u r e d surface-water H 0 concentration, t h e decay rate c o n stants, a n d bacterial c e l l counts for t h e five samples o b t a i n e d o n t h e transect. A l t h o u g h t h e a m b i e n t concentration o f H 0 r e m a i n e d s i m i l a r t h r o u g h o u t the transect, t h e decay rate decreased to g i v e H 0 half-lives o f 2 . 5 - 1 2 h . T h e c e l l n u m b e r s w e r e s i m i l a r at a l l s a m p l i n g locations, a n d t h e decay rate d i d n o t appear to correlate w e l l . F o r some u n e x p l a i n e d reason t h e increase 2

2

2

2

2

2


12.

COOPER ET AL.

Distribution

of H 0 2

2

409

in Surface Waters

Table V. Hydrogen Peroxide Profile and Decay at Two Stations i n the Chesapeake Bay


Water Depth (m)

Rate Constant (min )

H 0/ (nm) 2

t (h)

li9

l

Bacterial cells/mL (x W)

North Basin, L a t 38°55'57" N ; Lon 76°23'17" W Surface 38.0 2.7 -0.00183 6.3 2.8 32.0 3.1 -0.00152 7.6 5.7 3.1 6.6 6.3 -0.00176 8.7 5.5 3.4 4.3 -0.00211 12.0 3.3 2.8 -0.00258 4.5 15.3 3.2 3.3 -0.00257 4.5 South Basin, L a t 38°40'58" N ; Lon 76°25'25" W Surface 24.0 2.8 -0.00242 4.8 5.0 12.2 4.2 3.9 -0.00273 10.0 4.1 4.0 6.3 -0.00289 12.1 4.0 10.3 -0.00255 4.5 15.1 3.2 3.9 NA -0.00364 20.2 NA 3.9 4.5 -0.00298 25.0 NA 3.4 3.8 -0.00338 26.5 NA 5.4 2.2 -0.00533 b

N O T E : Decay was determined in the dark at approximately 10 °C. "Ambient concentration when water samples were brought on board. NA indicates not analyzed. fe

i n salinity m a y have r e s u l t e d i n l o n g e r half-lives. A d d i t i o n a l w o r k is necessary to b e t t e r u n d e r s t a n d these results. S e v e r a l s h i p b o a r d e x p e r i m e n t s w e r e c o n d u c t e d i n a n attempt to determ i n e t h e relative i m p o r t a n c e o f b i o l o g i c a l a n d c h e m i c a l processes i n t h e decay o f H 0 . A water sample f r o m 2.8 m ( N o r t h Basin) was h e a t e d to 6 2 - 6 5 °C for 30 m i n , a n d t h e decay of H 0 was m e a s u r e d . I n a p a r a l l e l e x p e r i m e n t , w a t e r f r o m 15.3 m was b o i l e d for 10 m i n a n d the H 0 c o n 2

2

2

2

2

2

Table V I . Hydrogen Peroxide Decay i n Surface-Water Samples i n the U p p e r Chesapeake Bay Sample (h) Tl Tl T2 T3 T4 T5

1025 1230 1350 1515 1624 1818

Salinity

Decay Rate (min' )

tl/* (h)

0.21 0.21 2.4 5.0 6.8 7.9

-0.00464 -0.00533 -0.00336 -0.00170 -0.00150 -0.00095

2.49 2.17 3.44 6.80 7.70 12.2

1

[HfiJo (nM) 81.5 99.4 71.7 72.6 75.6 83.5

Bacterial cells! mL(x 10 ) 6

2.1 2.3 2.7 3.6 2.6 3.0

N O T E : Samples were taken within 1 m of the water surface.


410


centration was m e a s u r e d w i t h t i m e . I n b o t h eases the H 0 c o n c e n t r a t i o n r e m a i n e d u n c h a n g e d after the treatment, for the d u r a t i o n o f the e x p e r i m e n t , a p p r o x i m a t e l y 30 h . T w o water samples o b t a i n e d at 5.7 m w e r e f i l t e r e d t h r o u g h m e m b r a n e filters. F i l t r a t i o n t h r o u g h e i t h e r 0.45- or 0 . 2 - μ π ι filters c o m p l e t e l y i n h i b i t e d H 0 decay over a 24-h p e r i o d . A t e v e r y s a m p l i n g p o i n t a l o n g the transect an u n f i l t e r e d a n d f i l t e r e d (0.22-μπι filter) sample was o b t a i n e d . A t a l l five locations the sample that h a d b e e n passed t h r o u g h a 0.22-μΐΉ filter s h o w e d no loss of H 0 over a 24-h p e r i o d . 2

2

2

2


2

2

O n e a d d i t i o n a l surface-water sample was o b t a i n e d f r o m the l o w e r reaches of the bay (location 6 i n F i g u r e 2) o n A p r i l 23, 1988. T h e salinity was 19°/^ o n an e b b i n g t i d e . T h e water, at 12 °C, c o n t a i n e d 5.4 Χ 10 b a c t e r i a / m L . T h e sample was r e t u r n e d to the laboratory a n d a l l o w e d to c o m e to r o o m t e m p e r a t u r e (29 °C o n the day of the study). H y d r o g e n p e r oxide was a d d e d at six concentrations (137, 216, 227, 541, 1076, a n d 2321 n M ) a n d the decay rate was d e t e r m i n e d . T h e decay rate constant was - 0 . 0 0 4 1 7 ± 0.00016 m i n (t = 2.8 h) for a l l samples, a result i n d i c a t i n g little or no effect of H 0 concentration o n the decay rate o v e r this range. T h i s result confirms that the decay rate constant is a robust p a r a m e t e r for use i n future m o d e l s . Because it is constant, it also shows that the decay rate is not a p p r o a c h i n g the m a x i m a l rate, w h e r e a d o u b l i n g of the c o n c e n tration w o u l d halve the rate constant. 6

1

2

m

2

T h e H 0 decay results o b t a i n e d i n the water samples o f the C h e s a p e a k e B a y are consistent w i t h b i o l o g i c a l processes i n the s h o r t - t e r m (M

in+1)+

2

>

M

+ OH- + O H "

(»+D+ + O H '

(20) (21)

If this m e c h a n i s m is i m p o r t a n t i n natural systems, i t w o u l d also l e a d to t h e formation o f the strongly o x i d i z i n g h y d r o x y l radical. T h i s process c o u l d have a significant effect o n the fate a n d transport of pollutants.

Distribution of

H0 2

2

H 0 has b e e n r e p o r t e d i n a l l surface waters s t u d i e d . I n lakes t h e d i s t r i b u t i o n is l i m i t e d to t h e e p i l i m n i o n a n d is consistent w i t h a s u n l i g h t (photochemical) pathway, a surface m a x i m u m , a n d decreasing concentration w i t h i n c r e a s i n g depth. W e measured H 0 i n the metalimnion and observed it i n the h y p o l i m n i o n . T h i s observation m a y b e e v i d e n c e of biologically m e d i a t e d (dark) formation, o r it may b e an e x p e r i m e n t a l artifact r e s u l t i n g f r o m l o w e r i n g t h e sampling equipment. 2

2

2

2


412


T h e s u n l i g h t - a b s o r b i n g matter is substantially m o r e c o n c e n t r a t e d i n the small lakes w e s t u d i e d than i n the m a r i n e systems (13). T h i s concentration results i n a d i s t r i b u t i o n p r i n c i p a l l y restricted to the e p i l i m n i o n , w h i c h m a y be as shallow as several meters. T h a t is, the total s u n l i g h t available for i n i t i a t i n g reactions that lead to the f o r m a t i o n of H 0 is the same as i n oceanic e n v i r o n m e n t s at s i m i l a r latitudes, b u t it is absorbed nearer to the surface i n lakes. A s a result, h i g h e r concentrations are o b s e r v e d i n the s m a l l h i g h h u m i c ( D O C ) freshwater systems e x a m i n e d . T h e G r e a t L a k e s are closer to oceanic systems i n terms of the d i s s o l v e d organic carbon, b u t the e p i l i m n i o n i n L a k e E r i e a n d L a k e O n t a r i o is usually less than 20 m (14). Downloaded by UNIV OF QUEENSLAND on April 26, 2016 | http://pubs.acs.org Publication Date: May 5, 1994 | doi: 10.1021/ba-1994-0237.ch012

2

2

T h e decay rates w e o b s e r v e d i n the freshwater systems (13, 14, 18) are h i g h e r than those r e p o r t e d for o l i g o t r o p h i c m a r i n e systems b u t s i m i l a r to near-shore (coastal) measurements (96). T h e increased decay rate w i t h red u c e d l i g h t penetration leads to larger d i e l variability i n H 0 concentrations. 2

2

W e m e a s u r e d H 0 v e r t i c a l profiles i n L a k e E r i e (14, 18) a n d n o t e d the s i m i l a r i t y w i t h oceanic profiles (23, 24). T h e major difference is the d e p t h to w h i c h H 0 is m i x e d i n oceanic e n v i r o n m e n t s . T o e m p h a s i z e the effect of solar radiation a n d w i n d speed o n the d i s t r i b u t i o n of H 0 i n the e p i l i m n i o n , w e m e a s u r e d four v e r t i c a l profiles of H 0 concentration a n d t e m perature i n Jacks L a k e o n 4 days, S e p t e m b e r 1 1 - 1 4 , 1990, a l l at 4:00 p . m . T h e 4 successive days w e r e q u i t e different i n w i n d speed a n d solar radiation. F i g u r e 7 shows the w i n d speed for the 4 successive days, a n d Table V I I summarizes the solar radiation m e a s u r e d o n the 4 days. T h e w i n d speed o n the c a l m days was v e r y s i m i l a r , a n d , except for the m o r e w i n d y early m o r n i n g o n the c l o u d y a n d w i n d y day, the w i n d y days w e r e q u i t e similar. F i g u r e 8 shows the v e r t i c a l water t e m p e r a t u r e a n d H 0 profiles o b t a i n e d at 4:00 p . m . for the 4 days. T h e s u n n y a n d c a l m day r e s u l t e d i n some surface w a r m i n g , b u t i n general the profiles are those t y p i c a l o f a w e l l m i x e d e p i l i m n i o n a n d p r o v i d e no c l u e to the H 0 profiles. Surface-water H 0 concentration was elevated o n the s u n n y a n d c a l m day ( S e p t e m b e r 11, 1990) a n d r a p i d l y decreased i n concentration w i t h d e p t h , as w o u l d be p r e d i c t e d f r o m the f o r m a t i o n rate studies c o n d u c t e d i n q u a r t z tubes a n d p r e s e n t e d i n F i g u r e 4. O n the f o l l o w i n g day, w h e n the w i n d speed was substantially h i g h e r a n d the insolation a p p r o x i m a t e l y the same, the H 0 was m i x e d d o w n t h r o u g h 7 - 8 m . Integration of the H 0 c o n c e n t r a t i o n o v e r the top 8 m of the water c o l u m n for the 2 days (Table V I I ) shows that the total a m o u n t of H 0 f o r m e d was v e r y s i m i l a r , 430 a n d 434 m g / m , a n d that the d i s t r i b u t i o n was g o v e r n e d b y p h y s i c a l m i x i n g . T h e 2 days w i t h clouds r e s u l t e d i n f o r m a t i o n of a decreased integrated concentration of H 0 , 281 a n d 176 m g / m . T h e c a l m day (September 13, 1990) s h o w e d features s i m i l a r to the s u n n y c a l m day except for the r e d u c e d surface H 0 c o n c e n t r a t i o n . T h e integrated H 0 concentration was h i g h e r for S e p t e m b e r 13, 1990, than for the c l o u d y w i n d y day because of h i g h e r solar radiation. 2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2


2

2

12.

COOPER ET AL.

6+

Distribution

Ο • Δ •

of H 0 2

in Surface Waters

2

413

SUNNY AND CALM SUNNY AND WINDY HAZY AND CALM CLOUDY AND WINDY

4+


2+

.

A ,

a

Α *

Ι

Α

/

A

A

"

p e T W »

Λ

"Α

,

10

Δ

20

TIME OF DAY (h) Figure 7. Wind speed in Sharpes Bay, Jacks Lake, September 11-14, 1990. T h e integrated H 0 concentration was d i r e c t l y r e l a t e d to t h e a l l o f the radiation measurements, b u t correlated best w i t h t h e u l t r a v i o l e t p o r t i o n ( r = 0.985). T o use this l i m i t e d data set, three assumptions n e e d to satisfied: 2

2

2

1. that H 0 days; 2

2. that H 0 2

2

decay is t h e same i n t h e water c o l u m n o v e r t h e 4

2

decay is t h e same w i t h d e p t h ; a n d

3. that H 0 decay is i n d e p e n d e n t o f H 0 the concentration range o b s e r v e d . 2

2

2

2

concentration o v e r

Table V I I . Daily Total Solar Radiation at the Surface of Jacks Lake and Integrated H 0 Concentration 2

2

Energy (langleys) Total Global

PAR"

UV

H0 (mg m )

505 456 241 113

254 229 129 63

22.1 20.4 11.8 6.6

430 434 281 176

2

Date Sept. Sept. Sept. Sept.

11, 1990 12, 1990 13, 1990 14, 1990

b

2

2

"PAR is photosynthetic active radiation. ''Calculated by integrating the H 0 concentration through the water column to 8 m. 2

2




414

H 0 2

2

CONCENTRATION (nM)

Figure 8. Temperature (top) and hydrogen peroxide (bottom) profiles in Sharpes Bay, Jacks Lake, Ontario, Canada, measured on September 11,1990, when conditions were sunny with no wind and on subsequent days that were sunny and windy, hazy and fairly calm, and cloudy and windy.


12.

COOPER ET AL.

Distribution

of H 0 2

2

in Surface Waters

415

W e d i d not measure decay rates o n successive days; h o w e v e r , other m e a surements give n o reason to expect large variations o v e r this short p e r i o d . T h e H 0 decay rate was d e t e r m i n e d at several depths o n o n e o f t h e days a n d was s h o w n to b e s i m i l a r i n a l l samples (Table II). W e have s h o w n o n several occasions that, i n the range of H 0 concentrations o b s e r v e d , t h e decay rate was first o r d e r w i t h respect to t h e o b s e r v e d H 0 concentrations. A l t h o u g h this approach is greatly s i m p l i f i e d , it appears that m o r e d e t a i l e d studies w o u l d h e l p to quantify t h e relationship o f solar radiation a n d H 0 formation a n d c y c l i n g i n natural waters. 2

2

2

2

2

2

2

T h e t e m p e r a t u r e data ( F i g u r e 8) suggest a w e l l - m i x e d e p i l i m n i o n . H o w ever, o n a short t i m e scale, t h e data f r o m t h e H 0 v e r t i c a l profiles indicate that t h e e p i l i m n i o n was not w e l l m i x e d , e v e n o n the w i n d y days. W e can c o n c l u d e f r o m this data that l o w - r e s o l u t i o n t e m p e r a t u r e - d e r i v e d m i x i n g rates are not applicable to H 0 d y n a m i c s i n these freshwater systems. I n fact, m a n y b i o l o g i c a l processes o f interest occur o n t i m e scales far shorter than 24 h . T h e possibility o f H 0 as a short-term tracer is i n t r i g u i n g , because it is a sensitive tracer for v e r t i c a l m i x i n g processes. 2


2

2

2

2

2

2

P h y s i c a l processes are i m p o r t a n t i n d e t e r m i n i n g t h e d i s t r i b u t i o n o f H 0 i n natural waters. I n oceanic e n v i r o n m e n t s a m o d e l that i n c l u d e s p h o t o c h e m i c a l formation a n d w i n d - a n d t e m p e r a t u r e - d r i v e n m i x i n g has b e e n d e v e l o p e d (25). I n freshwater systems, w h e r e the f o r m a t i o n of H 0 is r e s t r i c t e d to the u p p e r regions (

Factors Affecting the Distribution of H2O2 in Surface Waters

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