H E L G O ~ D E R MEERESUNTERSUCHUNGEN Helgoltinder Meeresunters. 33,422-433 (1980)
Impact of p o w e r - p l a n t discharges o n marine
z o o p l a n k t o n : A r e v i e w of thermal, m e c h a n i c a l and
biocidal effects
J. M. Capuzzo
Woods Hole Oceanographic Institution; Woods Hole, Massachusetts 02543, USA
ABSTRACT: The relative importance of thermal, mechanical and biocidal stresses to marine zooplankton entrained in cooling waters from coastal power-plant operations is dependent on specific features of power-plant design and siting. Toxic effects of power-plant operations will vary with (1) the degree of mechanical stress induced by pumping velocities of cooling water; (2) the physical and chemical interaction of receiving and discharge waters; (3) the dosage of chlorine or other biocide added to cooling waters for fouling control; (4) the exposure time to stress conditions experienced during passage through condenser conduits and discharge canals~ and (5) the nature of receiving waters, affecting the production and availability of the various halogen toxicants formed upon chlorination of seawater. Because of these variables, the problem of entrainment-induced mortality of zooplankton and the resulting effects on secondary production in receiving waters is difficult to assess. A review of laboratory and field studies addressing these problems is presented and particular emphasis given to the synergistic effect of multiple stresses.
I N T R O D U C T I O N
T h e i n c r e a s e d d e m a n d for coastal p o w e r stations has b e e n c o m p l e m e n t e d b y a n i n c r e a s e d c o n c e r n over the e n v i r o n m e n t a l i m p a c t of p l a n k t o n e n t r a i n m e n t i n a s s o c i a t e d c o o l i n g waters. E n t r a i n e d p l a n k t e r s m a y b e s u b j e c t e d to thermal, m e c h a n i c a l a n d b i o c i d a l stresses d u r i n g their p a s s a g e t h r o u g h c o n d e n s e r conduits. In s e v e r a l r e c e n t field studies, d e c r e a s e d p r o d u c t i v i t y of e n t r a i n e d p h y t o p l a n k t o n ( M o r g a n & Stross, 1969; H a m i l t o n et al., 1970; C a r p e n t e r et al., 1972) a n d r e d u c e d s u r v i v a l of e n t r a i n e d zoo- p l a n k t o n ( C a r p e n t e r et al., 1974a~ Davies & J e n s e n , 1975; H e i n l e , 1976) h a v e b e e n o b s e r v e d a n d h a v e r e s u l t e d i n c o n c e r n that p o w e r - p l a n t e n t r a i n m e n t a n d d i s c h a r g e s m i g h t alter p r i m a r y a n d s e c o n d a r y p r o d u c t i o n i n coastal r e c e i v i n g waters.
E n t r a i n m e n t - i n d u c e d m o r t a l i t y of m a r i n e z o o p l a n k t o n m a y b e a result of t h e r m a l shock d u e to excessive i n c r e a s e s i n A T b e y o n d the t h e r m a l t o l e r a n c e s of e n t r a i n e d species, r a p i d p r e s s u r e c h a n g e s a n d a b r a s i o n a s s o c i a t e d w i t h m e c h a n i c a l stress, or the b i o c i d a l a c t i o n of c h l o r i n e or other biocides. C u r r e n t c h l o r i n a t i o n practices for f o u l i n g control at coastal p o w e r stations v a r y from c o n t i n u o u s l o w - l e v e l a p p l i c a t i o n (0.1 m g 1-1 total r e s i d u a l chlorine), c o m m o n l y p r a c t i c e d i n G r e a t Britain (Beauchamp, 1969), to i n t e r m i t t e n t a d d i t i o n s (2-3 h p e r day), c o m m o n l y p r a c t i c e d i n t h e U n i t e d States (Becket & Thatcher, 1973). I n t h e latter i n s t a n c e c o n c e n t r a t i o n s of c h l o r i n e i n d i s c h a r g e d c o o l i n g w a t e r s are i n t h e r a n g e of 0.05-1.00 m g 1 -~ total r e s i d u a l c h l o r i n e (Brungs, 1973) a n d
Power-plant discharges 423
concentrations within this range have been shown to be toxic to serveral species of marine zooplankton (Roberts et al., 1975; Capuzzo et al., 1976; Capuzzo, 1979a). Evaluating the toxicity of chlorine to marine zooplankton is complicated by the produc- tion of several halogen toxicants upon chlorination of seawater. Wong & Davidson (1977) confirmed that chlorine is readily replaced by free bromine compounds in seawater with low ammonia concentrations. In the presence of high ammonia and/or organic concen- trations, significant production of combined halogen compounds as haloamines (Johan- nesson, 1958) and organohalogen compounds (Jolley, 1975) may occur.
The relative importance of thermal, mechanical and biocidal stresses to marine zooplankton entrained in cooling waters from coastal power-plant operations will vary with specific features of power-plant design, siting and operating procedures. The objective of this review is to summarize and evaluate the existing data from field and laboratory studies on the impact of coastal power plants on populations of marine zooplankton.
FIELD STUDIES
Carpenter et al. (1974a) reported copepod mortality of ~ 70 % as a result of entrain- ment in the cooling water system of the Millstone Nuclear Power Station, located on Long Island Sound (USA). They concluded that the observed mortality was due predo- minantly to mechanical damage; the impact of thermal and chlorine stresses could not be identified in the absence of mechanical stress. Zooplankters were not immediately killed by power-plant passage but died after several days in the effluent ponds adjacent to the power plant. The authors estimated that this loss of copepods resulted in a reduction of 0.1-0.3 % of the zooplankton production of Long Island Sound. In further studies (Carpenter et al., 1974b), no decrease in zooplankton populations could be detected in the receiving waters adjacent to the power plant; however, the authors concluded that conventional sampling techniques were inadequate in assessing small changes in zooplankton abundance.
Heinle (1976) compared zooplankton entrainment at three fossil-fueled power plants in Maryland (USA) and concluded that thermal and mechanical stresses had little effect on entrained zooplankton but extensive zooplankton mortality was observed during periods of chlorination. In earlier studies by Heinle (1969) at the Chalk Point power plant survival of entrained zooplankton was poor when discharge temperatures
exceeded 30 ~ presumably due to the combined effects of thermal and chlorine
stresses; however, standing crop and production of Acartia tonsa (the dominant zoo-
plankter) were somewhat greater during the summer following power-plant operations in comparison with pre-operational studies.
Gentile et al. (1976) in field studies at a power plant located on Narragansett Bay
observed complete mortality of the copepod Acartia tonsa during periods of chlorination
(1-3 mg 1-1) but no mortality in the absence of chlorination; other species of copepods
{e.g., Acartia clausl) were susceptible to thermal stress as well.
424 J . M . Capuzzo
mortality was observed; however, prolonged exposure of both cold and warm acclimated zooplankton to a high AT resulted in reduced survival The responses of entrained zooplankton to chlorination were varied at different power plants, but might have been related to synergistic effects of temperature, exposure time, salinity and water quality of receiving waters. Although reduced survival of entrained zooplankton had been observed by Davies and Jensen, little reduction in zooplankton populations could be detected beyond the mixing zone of the discharged effluent. Youngbluth (1976), how- ever, concluded that power-plant operations in a subtropical area resulted in a reduction
in diversity of the zooplankton community, where Acartia tonsa was the dominant
zooplankton in a thermal cove receiving discharged effhients.
To assess the sublethal effects of thermal discharges on zooplankton populations,
Gaudy (1977) compared the respiratory metabolism of the copepod Acartia d a u s i
coUected at the intake and discharge (AT -- 6 ~ of the Martigues-Ponteau power plant in the Gulf of Fos, Mediterranean Sea, and adjacent receiving waters affected by the heated effluents. Seasonal variations in respiration rates and Q10 were observed, but organisms collected from the heated effluents had reduced metabolic rates; copepods exposed to a simulated thermal stress showed similar reductions in metabolic rates.
Gaudy suggested that the reductions in respiration rates of Acartia clausi might offer
some physiological advantage in compensating the effects of thermal shock but further identification of these metabolic responses was needed.
As part of a three-year research program at the Woods Hole Oceanographic Institu- tion to assess the combined effects of temperature and chlorine on marine plankton,
collections of the copepod Acartia tonsa were made at the intake and discharge of the
Cape Cod Canal Generating Station on Cape Cod Bay, Massachusetts {USA), and the Montaup Generating Station, Narragansett Bay, Massachusetts (USA); respiration rates were determined for organisms from the intake samples and compared with organisms from the discharge samples taken during periods with and without chlorination. Sam- ples of zooplankton were collected using a 316-/tm plankton net and the temperature and residual chlorine level of each sample were recorded. Immediately after collection,
three replicates of twenty individuals of A. tonsa were isolated from each sample and
placed in 5-ml microrespirometer flasks (Grunbaum et at., 1955) with 4 ml filtered seawater. Respiration rates of copepods were measured at 22 ~ at 15-min intervals for 90 min. The results of these experiments are presented in Table I.
Copepods coUected in the discharge at the Montaup Plant for the periods May through October 1976 and 1977 survived plant passage but showed a significant reduction (P < 0.05) in respiration rate compared with organisms collected at the intake; no significant difference, however, was observed between organisms collected before and during chlorination. Copepods collected during July and August 1976 and 1977 at the Cape Cod Canal Plant did not survive plant passage, probably because of the high AT of discharge waters. The results of respiration rate measurements of copepods collected during September and October 1976 and 1977 were similar to results obtained at Montaup.
P o w e r - p l a n t d i s c h a r g e s 425
Table 1. Acartia tonsa. Respiration rates of individuals collected at the intake and discharge of the Montaup Generating Station (Narragansett Bau and the Cape Cod Canal Generating Station {Cape Cod Bay, USA}. Mean temperatures recorded during June through September at Montaup and September through early October at Cape Cod Canal. Total chlorine residual (C12mg1-1) measured by amperometric titration {Fischer and Porter Model No. 17T1010). Respiration rates
measured at 22 ~ (_+ 1 standard error~ N = 15)
Power plant Sample T ~ C12 mg 1-1 Respiration rate
(/~1 02 [h 9 100 animals] -1)
Montaup Intake 22.4 - - 9.2 (0.02)
Discharge 28.8 - - 3.4 {0.02}
Discharge + C12 28.8 0.08 3.2 {0.2)
Cape Cod Canal Intake 17.2 - - 8.4 (0.2}
Discharge 29.8 - - 3.6 {0.2}
Discharge + C l 2 29.8 0.10 3.4 (0.2}
c o p e p o d s w e r e fed d a i l y rations of the d i a t o m P h a e o d a c t y l u m t r i c o r n u t u m {1 • 104 cells m1-1) a n d e g g p r o d u c t i o n w a s e v a l u a t e d after 1 w e e k . E g g - p r o d u c t i o n rates of f e m a l e c o p e p o d s from i n t a k e a n d d i s c h a r g e s a m p l e s are p r e s e n t e d i n T a b l e 2. A s i g n i f i c a n t d e c r e a s e (P < 0.05) i n e g g p r o d u c t i o n w a s m e a s u r e d a m o n g copepods collected i n the c h l o r i n a t e d d i s c h a r g e s a m p l e s from b o t h p o w e r plants. No s i g n i f i c a n t difference, how- ever, w a s o b s e r v e d a m o n g c o p e p o d s collected i n the i n t a k e a n d n o n - c h l o r i n a t e d dis- c h a r g e s a m p l e s from b o t h p o w e r p l a n t s .
A s u m m a r y of the v a r i o u s field s t u d i e s is p r e s e n t e d i n T a b l e 3. As e v i d e n c e d b y the w i d e r a n g e of r e s p o n s e s of e n t r a i n e d z o o p l a n k t o n o b s e r v e d i n the v a r i o u s studies, the d e g r e e of e n t r a i n m e n t - i n d u c e d stress w i l l v a r y w i t h specific e n v i r o n m e n t a l v a r i a b l e s - i n c l u d i n g t e m p e r a t u r e , w a t e r q u a l i t y a n d d u r a t i o n of stress. I n order to o b t a i n r e l i a b l e d a t a for u s e i n p r e d i c t i n g the i m p a c t of e n t r a i n m e n t o n z o o p l a n k t o n p o p u l a t i o n s , s e v e r a l l a b o r a t o r y s t u d i e s s i m u l a t i n g p o w e r - p l a n t c o n d i t i o n s h a v e b e e n c o n d u c t e d .
Table 2. Acartia tonsa. Egg production rates of individuals collected at the intake and discharge of the Montaup Generating Station (Narragansett Bay, USA) and the Cape Cod Canal Generating Station (Cape Cod Bay, USA). Mean egg production rates measured at 20 ~ and a food density of
1 • 104 cells m1-1 (+- 1 standard error~ N = 15)
Power plant Sample Egg production rate
(eggs [female 9 d] -1)
Montaup Intake 3.2 (0.2)
Discharge 3.4 (0.1)
Discharge +C12 1.9 (0.1)
Cape Cod Canal Intake 3.8 (0.2)
Discharge 3.4 (0.2)
426 J . M . C a p u z z o L A B O R A T O R Y STUDIES
T h e s i n g u l a r a n d c o m b i n e d effects of t h e r m a l a n d c h l o r i n a t i o n stress on m a r i n e z o o p l a n k t o n h a v e b e e n e v a l u a t e d in s e v e r a l l a b o r a t o r y studies. H e i n l e (1969) f o u n d the u p p e r l i m i t of t h e r m a l t o l e r a n c e for Acartia tonsa to b e b e t w e e n 30 o a n d 35 ~ w h e n a c c l i m a t i o n t e m p e r a t u r e s w e r e b e t w e e n 20 ~ a n d 25 ~ a n d b e t w e e n 25 o a n d 30 ~ w h e n a c c l i m a t i o n t e m p e r a t u r e s w e r e b e t w e e n 5 ~ a n d 10 ~ R e e v e & C o s p e r (1972), h o w e v e r , f o u n d t h a t a s u b t r o p i c a l p o p u l a t i o n of A. tonsa, a c c l i m a t e d to 30 ~ c o u l d s u r v i v e at
Table 3. Summary of zooplankton entrainment studies at coastal power plants
Location
Power plant
Generating Water
capacity demand
(gw) (m 3 h "l)
Principal stress Reference
Millstone Point 650 95,000
Long Island Sound (USA)
Chalk Point 730 114,000
Patuxent River, MD (USA)
Vienna 240 12,600
Nanticoke River, MD (USA)
Morgantown 1140 222,000
Potomac River, MD (USA)
Brayton Point 650 154,000
Narragansett Bay (USA)
Marshall Station 2136 230,400
Lake Norman, NC (USA)
Chesterfield 1 4 1 6 1 5 8 , 4 0 0
James River, VA (USA)
Indian River 347 61,200
Indian River, DL (USA)
Guayanilla Bay 1 0 7 3 138,000-
(Puerto Rico) 234,000
Martigues-Ponteau - - - -
Mediterranean Sea (France)
Montaup 500 12,250
Narragansett Bay (USA)
Cape Cod Canal 1100 78,000
Cape Cod Bay (USA)
mechanical Carpenter et al.
(1974a, h) chlorine, slight Heinle (1976) thermal
no significant stress Heinle (1976)
chlorine, slight Heinle (1976) thermal
chlorine, thermal Gentile et al. (1976)
thermal Davies & Jensen
(1975)
thermal, Davies & Jensen
chlorine (>0.50 mgl 1) (1975}
mechanical (?) Davies & Jensen chlorine (>1.00 mgl 1) (1975)
thermal
thermal, chlorine
thermal, chlorine
Youngbluth (1976) Gaudy (1977) this study
Power-plant discharges
427
35 ~ G o n z a l e s (1974) c o m p a r e d t h e critical t h e r m a l m a x i m a a n d u p p e r l e t h a l t e m p e r a - tures of A. tonsa a n d A. clausi. A. tonsa w a s f o u n d to h a v e a w i d e r t h e r m a l r a n g e t h a n A. clausi a n d therefore has a r e l a t i v e l y b e t t e r capacity to w i t h s t a n d t h e r m a l stress. G o n z a l e s s u g g e s t e d that the t h e r m a l a d a p t a t i o n of A. tonsa is m a n i f e s t e d i n the shifting of l e t h a l limits, r e p r o d u c t i o n a n d m e t a b o l i c activities i n r e s p o n s e to the a c c l i m a t i o n t e m p e r a t u r e , a l l o w i n g this species to tolerate a w i d e r a n g e of t h e r m a l stresses. O n e could c o n c l u d e from t h e s e f i n d i n g s that a c c l i m a t i o n t e m p e r a t u r e is a n i m p o r t a n t factor i n t h e r m a l t o l e r a n c e a n d that t h e r m a l stress from p o w e r - p l a n t o p e r a t i o n s is less severe for e u r y t h e r m a l s p e c i e s t h a n s t e n o t h e r m a l ones.
To c o m p a r e t h e effects of free a n d c o m b i n e d h a l o g e n toxicants a n d t e m p e r a t u r e o n
Acartia tonsa, c o n t i n u o u s flow b i o a s s a y u n i t s w e r e d e s i g n e d t o a l l o w short-term toxicant a n d / o r t h e r m a l stress, r a p i d e l i m i n a t i o n of these stress conditions, a n d s u b s e q u e n t l o n g - t e r m o b s e r v a t i o n of t h e test o r g a n i s m s (Capuzzo et al., 1976). T h e toxicity of free c h l o r i n e a n d c h l o r a m i n e to copepods a c c l i m a t e d at 10 ~ w i t h A 0 ~ A 5 o a n d A 10 ~ i n c r e a s e s i n e x p o s u r e t e m p e r a t u r e a n d copepods a c c l i m a t e d at 20 ~ w i t h A 0 o, A 5 ~ A 8 o a n d A 10 ~ i n c r e a s e s i n e x p o s u r e t e m p e r a t u r e w e r e compared. C o p e p o d s w e r e e x p o s e d to the t e m p e r a t u r e - t o x i c a n t stress for 30 m i n a n d m o r t a l i t y w a s a s s e s s e d 48 h later u s i n g the n e u t r a l r e d s t a i n i n g t e c h n i q u e d e s c r i b e d b y C a p u z z o (1979b}. After the 3 0 - m i n exposure, r e s i d u a l h a l o g e n l e v e l s w e r e c h e m i c a l l y e l i m i n a t e d b y the a d d i t i o n of s o d i u m t h i o s u l f a t e a n d t h e t e m p e r a t u r e w a s r e d u c e d to the a c c l i m a t i o n t e m p e r a t u r e . Control e x p e r i m e n t s i n c l u d e d e x p o s u r e of copepods to the t e m p e r a t u r e stresses with no toxicant a d d i t i o n s a n d e x p o s u r e to s e a w a t e r p r e v i o u s l y d e c h l o r i n a t e d w i t h s o d i u m thiosulfate. T h e c o p e p o d s w e r e n o t fed d u r i n g the e x p o s u r e p e r i o d b u t w e r e m a i n t a i n e d o n t h e d i a t o m P h a e o d a c t y l u m tricornutum (1 • 104 cells m1-1) d u r i n g the r e m a i n d e r of the 48-h e x p e r i m e n t a l period.
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Pig. 1. Acartia tonsa. Percent mortality 48 h after 30-min exposure to applied free chlorine at 10 ~ 15 ~ and 20 ~ copepods acclimated at 10 ~ open circles - control mortality; open half-circles - dechlorinated before addition of
test organisms
Pig. 2. Acartia tonsa. Percent mortality 48 h after 30-min exposure to applied chloramine at 10 ~ 15 ~ and 20 ~ copepods acclimated at 10 ~ open circles - control mortality; open half-circles - dechlorinated before addition of
428 J . M . C a p u z z o
20~, c . . . . , , , , i , , ~ , l e e / - - , ~
5 0 ~
2 5 ~ ~ / / o
>., '~ 5s
I IIIIII I I " "i ";,"l~,": 1
5C ,, i " ~ ~ '-4
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I i i l l l l J l j , , I , , , , I0.t 0.5 t.0 5.0 t0.0 2 5 . 0 A p p l i e d f r e e c h l o r i n e ( m g / I )
Fig. 3. Acartia tonsa. Percent mortality 48 h after 30-rain exposure to applied free chlorine at
20 ~ 25 ~ and 28 ~ copepods acclimated at 20 ~ open circles - control mortality; open half-circles - dechlorinated before addition of
test organisms
t 0 0 2 6 o c ' ' I ' ' " 1 ' ' I ~/~'1 '
2 5 ~ ~ / . o .# >.
-~ 5 0 . . ~ ~ -
;-,T, J
0 l I I I I , , I . . . . t i ~ ,i I
2 8 ~ / ,
o , ,-"TT .... I , ,,I .... I o.t 0.5 t.0 5.0 ~0,0 2 5 . 0
A p p L i e d c h L o r a m i n e ( m g / L )
Fig. 4. Acartia tonsa. Percent mortality 48 h after 30-rain exposure to applied chloramine at 20 ~ 25 ~ and 28 ~ copepods acclimated at
20 ~ open circles - control mortality; open half-circles - dechlorinated before addition of
test organisms
T o x i c a n t c o n c e n t r a t i o n s are reported as b o t h a p p l i e d a n d r e s i d u a l levels. I n all tests c h l o r a m i n e w a s more toxic t h a n free c h l o r i n e to copepods. For c o p e p o d s a c c l i m a t e d at 10 ~ there w a s n o effect of t e m p e r a t u r e o n the toxicity of e i t h e r h a l o g e n form (Figs 1 a n d 2). For copepods a c c l i m a t e d at 20 ~ no effect of t e m p e r a t u r e w a s o b s e r v e d at 25 ~ or 28 ~ (Figs 3 a n d 4); however, at 30 ~ t h e r m a l stress a l o n e r e s u l t e d i n 60 % m o r t a l i t y of test o r g a n i s m s a n d h i g h e r mortality w a s o b s e r v e d w i t h e x p o s u r e to t h e toxicants. A c o m p a r i s o n of LCs0 v a l u e s ( a p p l i e d a n d residual) at the v a r i o u s t o x i c a n t - t e m p e r a t u r e stresses is p r e s e n t e d i n T a b l e 4. It is c o n c l u d e d , therefore, that t h e r m a l effects o n c h l o r i n e toxicity are only i m p o r t a n t w h e n this species' t h e r m a l l i m i t is a p p r o a c h e d .
In l a b o r a t o r y e x p e r i m e n t s w i t h other species of z o o p l a n k t o n - b o t h h o l o p l a n k t o n i c a n d m e r o p l a n k t o n i c forms - the s y n e r g i s t i c effect of t e m p e r a t u r e i n e n h a n c i n g the toxic effects of c h l o r i n a t e d c o o l i n g waters h a s b e e n d e m o n s t r a t e d (Capuzzo, 1979a); this effect is p o s s i b l y d u e to a n i n t e r a c t i o n of u p t a k e rates a n d r e g u l a t i o n of p h y s i o l o g i c a l rates a n d the greatest e n h a n c e m e n t i n s e n s i t i v i t y could b e e x p e c t e d at the u p p e r l i m i t of t h e r m a l tolerance. G e n t i l e et al. {1976) a n d H e i n l e & B e a v e n {1977) h a v e d e m o n s t r a t e d the s y n e r g i s t i c effect of exposure time o n the toxicity of c h l o r i n a t e d s e a w a t e r to m a r i n e copepods.
T h e o n l y e s t i m a t e s of the toxicity of a l t e r n a t i v e b i o c i d e s ( b r o m i n e chloride, ozone, etc.) to m a r i n e z o o p l a n k t o n are the d a t a r e p o r t e d b y B r a d l e y (1977) o n the c o m p a r i s o n of b r o m i n e chloride a n d chlorine toxicity to the copepods Eurytemora affinis a n d Acartia tonsa. T h e r e w a s n o s i g n i f i c a n t difference i n the toxicity of e i t h e r b i o c i d e a n d this m i g h t s u g g e s t that the a d d i t i o n of b r o m i n e chloride to s e a w a t e r results i n the p r o d u c t i o n of h a l o g e n toxicants s i m i l a r to those p r o d u c e d u p o n c h l o r i n a t i o n of seawater.
P o w e r - p l a n t d i s c h a r g e s 429
Table 4. Acartia tonsa. Comparison of LCs0 values of chlorine and chloramine for individuals acclimated at 10 ~ and 20 ~
Temperature (~ Chlorine LCs0 - mg 1 t Chlorine*
Acclimation Exposure toxicant applied residual +
10 10 free chlorine 4.80 0.82
15 4.80 0.82
2O 4.80 O.82
10 chloramine 2.10 0.34
15 1.50 0.23
20 1.50 0.23
20 20 free chlorine 4.80 0.82
25 5.00 0.86
28 4.80 0.82
20 chloramine 2.00 0.32
25 2.00 0.32
28 2.00 0.32
*LCs0 values determined by log-probit analysis (Finney, 1971)
+ Chlorine (or its derivatives) disappears from seawater fairly rapidly but the reasons for this disappearance or "chlorine d e m a n d " have b e e n difficult to identify (Goldman et al., 1979). The "lost chlorine" must remain suspect as the basis for potentially toxic compounds to marine biota. In these experiments y (residual) = 0.18 x (applied) - 0.04, r = 0.88, N = 30
e x p o s u r e p e r i o d c o p e p o d s w e r e m a i n t a i n e d o n a d i a t o m c u l t u r e of P h a e o d a c t y l u m (1 X 104 c e l l s m1-1) at 20 ~ a n d e g g p r o d u c t i o n w a s e v a l u a t e d for I w e e k f o l l o w i n g e x p o s u r e . A l t h o u g h t h e g r o w t h r a t e s of i n d i v i d u a l c o p e p o d s t a g e s w e r e n o t e s t i m a t e d , t h e d u r a t i o n of d e v e l o p m e n t f r o m e g g to a d u l t w a s e s t i m a t e d for b o t h c o n t r o l a n d e x p o s e d g r o u p s .
T h e e g g - p r o d u c t i o n r a t e s of e a c h g r o u p of c o p e p o d s a r e p r e s e n t e d i n T a b l e 5. E g g - p r o d u c t i o n r a t e s w e r e s i g n i f i c a n t l y r e d u c e d (P < 0.05) for b o t h c h l o r i n e a n d c h l o r a m i n e e x p o s e d g r o u p s , b u t t h e r e w a s n o s i g n i f i c a n t d i f f e r e n c e i n t h e e f f e c t of e i t h e r t o x i c a n t or i n d e v e l o p m e n t t i m e ( ~ 18 days) for a n y of t h e t h r e e g r o u p s . F r o m t h e m e a n v a l u e s of e g g s p e r f e m a l e p e r d a y (E) a n d t h e d u r a t i o n of d e v e l o p m e n t (D), t h e d a i l y p o p u l a t i o n r e p r o d u c t i v e r a t e (B) w a s c a l c u l a t e d (B = E / D ) . T h e s e r e s u l t s a r e p r e s e n t e d i n T a b l e 5. Table 5. Acartia tonsa. Egg production of individuals exposed to free chlorine or chloramine in laboratory experiments. M e a n e g g production rates measured at 20 ~ and a food density of I X 104
cells ml "t ( _ 1 standard error; N = 12)
Toxicant Eggs (female-day) -z Daily population reproductive rate
(E) (B)
C o n t r o l 4.0 (0.1) 0.22
Free chlorine* 1.8 (0.2) 0.10
(1.00 m g 1-1)
Chloramine* 1.6 (0.1) 0.09
(1.00 m g 1 "1)
430 J . M . C a p u z z o
In a s i m i l a r s t u d y (Capuzzo, 1979b) the effects of the h a l o g e n t o x i c a n t s on the
f e e d i n g r a t e s a n d e g g p r o d u c t i o n r a t e s of the rotifer
Brachionus pficatilis
w e r e e v a l u -ated. Rotifers s u r v i v i n g e x p o s u r e to e i t h e r c h l o r i n e or c h l o r a m i n e h a d s i g n i f i c a n t l y l o w e r f e e d i n g r a t e s a n d e g g - p r o d u c t i o n r a t e s t h a n c o n t r o l a n i m a l s . T h e r e d u c e d r e p r o d u c t i o n r a t e s w e r e not s u s t a i n e d b y t h e s e c o n d g e n e r a t i o n of rotifers a n d it w o u l d a p p e a r t h a t s h o r t - t e r m e x p o s u r e to c h l o r i n a t e d s e a w a t e r d o e s not r e s u l t in a p e r m a n e n t a l t e r a t i o n in the r e p r o d u c t i v e p o t e n t i a l of z o o p l a n k t o n p o p u l a t i o n s .
In l a b o r a t o r y b i o a s s a y s w i t h m e r o p l a n k t o n i c o r g a n i s m s , t h e s e n s i t i v i t y of l a r v a l
l o b s t e r s
(Homarus americanus;
C a p u z z o et al., 1976), l a r v a l o y s t e r s(Crassostrea vir-
ginica;
C a p u z z o , 1979a) a n d j u v e n i l e k i l l i f i s h(Pundulus heteroclitus;
C a p u z z o , 1979a) to c h l o r i n a t e d s e a w a t e r h a s b e e n d e m o n s t r a t e d . In a d d i t i o n to a c u t e toxic effects, e x p o s u r e of l a r v a l l o b s t e r s to s u b l e t h a l c o n c e n t r a t i o n s r e s u l t e d i n r e d u c e d r e s p i r a t i o n r a t e s a n d g r o w t h r a t e s (Capuzzo, 1977), s u g g e s t i n g t h a t the h a l o g e n t o x i c a n t s i n t e r f e r e w i t h e n e r g y m e t a b o l i s m .C O N C L U S I O N S
A i t h o u g h m e c h a n i c a l , t h e r m a l a n d b i o c i d a l stresses of c o n d e n s e r p a s s a g e h a v e b e e n s h o w n to affect the s u r v i v a l of z o o p l a n k t o n e n t r a i n e d at c o a s t a l p o w e r stations, a l t e r a t i o n s in s e c o n d a r y p r o d u c t i o n of r e c e i v i n g w a t e r s h a v e not b e e n d e m o n s t r a t e d . A t p o w e r - p l a n t sites w h e r e a d e q u a t e d i l u t i o n of c o o l i n g w a t e r s is p r o v i d e d e v e n t h e effects of b i o c i d a l stress to z o o p l a n k t o n p o p u l a t i o n s m a y not c a u s e a s e r i o u s r e d u c t i o n in s e c o n d a r y p r o d u c t i v i t y b e c a u s e of the s m a l l p e r c e n t a g e of t h e z o o p l a n k t o n a f f e c t e d a n d t h e h i g h r e p r o d u c t i v e r a t e s of u n a f f e c t e d z o o p l a n k t o n . T h e m o s t s e r i o u s i m p a c t of p o w e r - p l a n t e n t r a i n m e n t m a y b e the r e d u c e d s u r v i v a l a n d / o r g r o w t h of t h e m e r o p l a n k - ton c o m p o n e n t of t h e z o o p l a n k t o n b e c a u s e of t h e i r s e a s o n a l a n d s p o r a d i c o c c u r r e n c e in the p l a n k t o n . Location of p o w e r p l a n t s , h o w e v e r , at sites w i t h p o o r d i l u t i o n of c o o l i n g w a t e r s a n d c o n t i n u o u s c r o p p i n g of t h e s a m e z o o p l a n k t o n p o p u l a t i o n s c o u l d r e s u l t in l o c a l i z e d r e d u c t i o n s in s e c o n d a r y p r o d u c t i v i t y , p o s s i b l e c h a n g e s in z o o p l a n k t o n com- m u n i t i e s a n d r e d u c e d l a r v a l r e c r u i t m e n t .
S p e c i f i c r e c o m m e n d a t i o n s to m i n i m i z e t h e i m p a c t of z o o p l a n k t o n e n t r a i n m e n t are: (1) c a r e f u l s i t i n g of n e w c o a s t a l p o w e r p l a n t s to p r o v i d e a d e q u a t e d i l u t i o n of effluents; (2) controi of t h e r m a l i n c r e a s e s to c o i n c i d e w i t h s e a s o n a l a m b i e n t t e m p e r a t u r e s a n d the t h e r m a l t o l e r a n c e s of d o m i n a n t z o o p l a n k t o n ; a n d (3) l o w - l e v e l c h l o r i n a t i o n c o m b i n e d w i t h d e c h l o r i n a t i o n a n d / o r r a p i d d i l u t i o n of c o o l i n g w a t e r s .
M o r e c o n c e r n s h o u l d b e p l a c e d on t h e i m p a c t of e n t r a i n m e n t - i n d u c e d stresses on l a r v a l o r g a n i s m s , p a r t i c u l a r l y w h e r e c o m m e r c i a l l y i m p o r t a n t s p e c i e s m a y b e a f f e c t e d a n d s i g n i f i c a n t r e d u c t i o n s in h a r v e s t a b l e crop m a y occur. T h e p h y s i o l o g i c a l a n d b e h a v i o r a l l i m i t a t i o n s of e n t r a i n e d l a r v a l s t a g e s a n d t h e p o s s i b l e a c c u m u l a t i o n a n d t r a n s f e r of o r g a n o h a l o g e n c o m p o u n d s in m a r i n e food c h a i n s h a v e not b e e n fully e x p l o r e d ; b o t h t h e s e p r o b l e m s m a y h a v e m o r e s e r i o u s c o n s e q u e n c e s for p o p u l a t i o n s of m a r i n e o r g a n i s m s t h a n t h e p r o b l e m of e n t r a i n m e n t - i n d u c e d m o r t a l i t y a n d s h o u l d b e the s u b j e c t of m o r e e x t e n s i v e r e s e a r c h .
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