Bull. Environ. Contam. Toxicol. (1992) 49:593-599 9 1992 Springer-Verlag New York Inc.
i
Envirorm'mntal
Effects of Chromium, Copper, Nickel, and Zinc on Survival and Feeding of the Cladoceran Moina macrocopa C. K. Wong Department of Biology, The Chinese University of Hong Kong, Shatin, N. T., Hong Kong Heavy metals are widely recognized as highly toxic and dangerous (Mance 1987). Past research activities on h e a v y m e t a l p o l l u t i o n in Hong Kong have e m p h a s i z e d coastal environments (Chan et al. 1974; Phillips 1989; Chu et al. 1990). Since the main sources of heavy metals are the discharge and spillage of w a s t e w a t e r from electroplating factories, concentrations of heavy metals in streams and pools near industrial areas may be higher than those in coastal waters. E l e c t r o p l a t i n g wastewater in Hong Kong contains high levels of chromium, copper, nickel and zinc. The toxicity of these heavy metals to aquatic organisms has been extensively reviewed (Mance 1987). Toxicity information for invertebrates shows that crustaceans are among the most sensitive organisms (Mance 1987). Of the crustacean species tested, cladocerans appear to be the most susceptible. Cladocerans are important components of many aquatic ecosystems. Despite their importance in many freshwater communities and their sensitivity to heavy metal toxicity, information on the toxicity of heavy metals to cladocerans is limited e x c e p t for several D a p h n i a species (Biesinger and Christensen 1972; Winner and Farrell 1976; Ingersoll and W i n n e r 1982). In Hong Kong the f r e s h w a t e r cladoceran Moina macrocopa occurs in small ponds and rice paddies and is mass cultured by some farmers as a high quality fish food. The objectives of this study are to determine the effects of various heavy metals on the survival and feeding of M. macrocopa.
MATERIALS
AND
METHODS
The freshwater cladoceran Moina macrocopa came from a continuous laboratory culture raised from a single parthenogenetic female. Experiments were carried out Send reprint requests to C.K.Wong at the above address
593
w i t h c o h o r t s of n e w b o r n (< 24 hr) n e o n a t e s o b t a i n e d by isolating egg-bearing adult females from the stock culture. Stock s o l u t i o n s (i.0 g/L) of m e t a l ions w e r e p r e p a r e d by d i s s o l v i n g the m e t a l l i c salts K~Cr~O7, C u S O 4 . 5 H ~ O , NicI2.6H20 and ZnSO4.7H20 i n a i s - t i l l e d wate-r. S o l u t i o n s for a c u t e t o x i c i t y e x p e r i m e n t s a n d f e e d i n g e x p e r i m e n t s w e r e p r e p a r e d by a d d i n g a l i q u o t s of s t o c k s o l u t i o n to f i l t e r e d ( W h a t m a n GF/C) u n c o n t a m i n a t e d w a t e r from a large (300 L) aquarium. A c u t e (48 hr) l e t h a l i t y e x p e r i m e n t s w e r e c a r r i e d o u t in 50 m L b e a k e r s c o n t a i n i n g 40 m L of t e s t s o l u t i o n (pH 6.5) a n d i0 a n i m a l s . F o o d c o n s i s t e d of a m i x t u r e of the a l g a e S p i r u l i n a sp. a n d Chlorella pyrenoidosa. Food c o n c e n t r a t i o n was d e t e r m i n e d f l u o r o m e t r i c a l l y by m e a s u r i n g t h e a m o u n t of c h l o r o p h y l l _a in the water w i t h a T u r n e r M o d e l 112 f l u o r o m e t e r . Initial food concentration w a s f i x e d a t i0 u g C h l a / L b e c a u s e r e s u l t s of an e a r l i e r s t u d y (Wong 1989) s h o w e d t h a t the gut fullness of M__~. m a c r o c o p a feeding o n C__~. p y r e n o i d o s a i n c r e a s e d w i t h f o o d c o n c e n t r a t i o n up to a b o u t i0 ug c h l a / L and then r e m a i n e d unchanged. Each m e t a l ion w a s t e s t e d at 6 to 7 c o n c e n t r a t i o n s . Four r e p l i c a t e s w e r e u s e d for e a c h c o n c e n t r a t i o n . The beakers were weakly illuminated during day time by n a t u r a l light. Temperature during experiments ranged from 24 to 27 ~ C. Test s o l u t i o n s w e r e r e n e w e d after 24 h r . Newborn animals produced a t 24 h r w e r e removed. The n u m b e r of s u r v i v i n g a n i m a l s was c o u n t e d after 24 and 48 hr of exposure. Moribund animals were examined under a dissecting microscope. Individuals w i t h o u t h e a r t b e a t s w e r e c o n s i d e r e d dead. The effects of v a r i o u s m e t a l s o n feeding o f M__~. m a c r o c o p a w e r e s t u d i e d at an e x p o s u r e e q u i v a l e n t to the 48 hr LC50 of each metal. For each experiment, 20 a n i m a l s w e r e e x p o s e d in a i00 m L b e a k e r c o n t a i n i n g 60 mL of test solution. Animals maintained in u n c o n t a m i n a t e d w a t e r w e r e u s e d as controls. Four to 6 r e p l i c a t e s i n v o l v i n g a t o t a l of > i00 a n i m a l s w e r e u s e d for each metal. Food in the form of the alga C__~. p y r e n o i d o s a was i n i t i a l l y p r o v i d e d at a c o n c e n t r a t i o n of a b o u t I0 u g C h l a / L . F e e d i n g of t h e a n i m a l s w a s m e a s u r e d a f t e r 0.5, 24 and 48 hr of m e t a l e x p o s u r e . P r i o r to the s t a r t of an e x p e r i m e n t , the c o n t e n t s of the beaker were examined and dead animals were removed. Feeding experiments began when small a l i q u o t s of C__~.p y r e n o i d o s a w e r e a d d e d to the b e a k e r s to raise the food concentration t o 50 u g C h l a / L . A f t e r 15 to 20 min of feeding, animals were collected on a 0 . 1 2 5 - m m m e s h s c r e e n and i n a c t i v a t e d by freezing. Gut f u l l n e s s (chlorophyll + phaeopigments) w a s u s e d as 594
~6~
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pssodxe
RdoooIEm
"H ]o
(%) X W ~ I g W a o H
(7/6''') UO!),RJ),UeOUOO e
9 I
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t, I
0 ;'0
Jq~ v 01,
I I
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chromium > zinc > n i c k e l has b e e n r e p o r t e d for D a p h n i a h y a l i n a (Baudouin and S c o p p a 1974). P r o b i t a n a l y s i s (Finney 1971) i n d i c a t e d t h a t c o p p e r was c l e a r l y m o r e t o x i c to M_~. m a c r o c o p a t h a n the other m e t a l s (Table i). T h e 24 and 48 h r L C 5 0 v a l u e s for c o p p e r w e r e one to s e v e r a l o r d e r s of m a g n i t u d e l o w e r t h a n t h o s e for the o t h e r m e t a l s . For copper, t h e r e was only a slight difference between t h e 24 h r L C 5 0 and 48 hr LC50. For the other metals, the 48 hr LC50 w a s l o w e r t h a n t h e 24 h r LC50. The difference was about twofold for chromium and zinc, and close to f o u r f o l d for nickel. T h e s e r e s u l t s d e m o n s t r a t e d that t h e r e was an increase in t o x i c i t y f o l l o w i n g p r o l o n g e d exposure. The order of both LC50 v a l u e s was n i c k e l > zinc > c h r o m i u m > copper.
T a b l e i. LCS0 v a l u e s (mg/L) of chromium, copper, nickel and zinc for M__=. m a c r o c o p a . 95% c o n f i d e n c e limits are i n d i c a t e d in p a r e n t h e s e s .
24 hr
48 hr
Cr
0.76
(0.69-0.83)
0.36
(0.29-0.40)
Cu
0.09
(0.08-0.10)
0.08
(0.07-0.09)
Ni
23.59
(12.99-34.19)
6.48
(5.55-7.41)
Zn
2.04
(1.75-2.33)
1.17
(1.02-1.32)
596
200
Cr 150
100
50
I
0
I
200
Cu
15o
100
0k .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
50
~
1 0
0
0
20O
I
Ni
ql,-.
0
I
'
150
100
................................
~ ................................
200
Zn
160
100
50
I
I
24
4B
Time (hr) F i g u r e 2. Gut f u l l n e s s of M. m a c r o c o p a a f t e r 0.5, 24 and 48 hr of e x p o s u r e to chromium, copper, n i c k e l and zinc at a c o n c e n t r a t i o n e q u i v a l e n t to t h e 48 hr LC50 of e a c h metal. Gut f u l l n e s s of c o n t r o l a n i m a l s is expressed as 100%. Each point represents the mean and range of 6 t o i0 fluorometer counts u s i n g a t o t a l of at least 60 animals.
597
C o m p a r i s o n a m o n g species is a p p r o x i m a t e because many e x p e r i m e n t a l v a r i a b l e s m a y a f f e c t toxicity. In t e r m s of L C 5 0 v a l u e s , M_~. m a c r o c o p a w a s l e s s s e n s i t i v e t o h e a v y m e t a l s than some of the D a p h n i a species. The 48 hr L C 5 0 of 0.08 m g C u / L for M__~.m a c r o c o p a w a s s i m i l a r to those reported f o r D__~.m a q n a (Biesinger and C h r i s t e n s e n 1972, K h a n g a r o t and R a y 1987) a n d h i g h e r t h a n t h o s e r e p o r t e d for D__~.p u l e x (Ingersoll and W i n n e r 1982) and D__~.h y a l i n a (Baudouin and Scoppa 1974). For c h r o m i u m , n i c k e l and zinc, 48 hr L C 5 0 v a l u e s for M_~. macrocopa were m u c h h i g h e r than t h o s e for D~. h y a l i n a (Baudouin and S c o p p a 1974). The f e e d i n g of M__~.m a c r o c o p a was m e a s u r e d a f t e r 0.5, 24 a n d 48 h r of e x p o s u r e to m e t a l s at concentrations equivalent t o t h e 48 h r L C 5 0 v a l u e of e a c h m e t a l (Figure 2). Gut fullness of a n i m a l s e x p o s e d to m e t a l s was e x p r e s s e d as a p e r c e n t a g e of the control. R e s u l t s were tested with 2 - w a y A N O V A w i t h e x p o s u r e t i m e and p r e s e n c e o r a b s e n c e of m e t a l as t h e m a i n f a c t o r s . V a r i a b i l i t y in gut fullness was h i g h a m o n g replicates. A s i g n i f i c a n t e f f e c t (P < 0.05) of m e t a l s w a s n o t e d for copper, c h r o m i u m and nickel, w h e r e a s s i g n i f i c a n t effects (P < 0.05) of e x p o s u r e t i m e w a s n o t e d f o r c o p p e r , c h r o m i u m a n d zinc. For all four metals, t h e r e was no e v i d e n c e of i n t e r a c t i o n b e t w e e n the m a i n factors. Animals exposed to c o p p e r for just 0.5 hr showed a 65 % r e d u c t i o n in gut fullness. A t 24 hr, gut fullness was depressed b y m o r e t h a n 50 % in a n i m a l s e x p o s e d to chromium, c o p p e r and nickel, and by a b o u t 30 % in a n i m a l s e x p o s e d to zinc. A c o n t i n u e d , but less pronounced, i n h i b i t o r y e f f e c t was o b s e r v e d at 48 hr. Gut fullness of s u r v i v i n g animals was r e d u c e d by a b o u t 58% in chromium, 77% in nickel, 42 % in z i n c a n d o n l y 14% in c o p p e r . Decreased food intake leads to lower r e p r o d u c t i v e c a p a c i t y which, in turn, may reduce population size. These results s u g g e s t e d that feeding is a u s e f u l i n d i c a t o r of m e t a l exposure.
Acknowledgments. The a u t h o r t h a n k s Ms. S.W. Hui for her h e l p in p e r f o r m i n g the experiments. This w o r k was supported by a grant from the Croucher Foundation, H o n g Kong. REFERENCES B i e s i n g e r KE, c h r i s t e n s e n GM (1972) E f f e c t s of v a r i o u s metals on survival, growth, reproduction, and m e t a b o l i s m of D a p h n i a maqna. J Fish Res Bd Can 29: 1691-1700 Baudouin MF, Scoppa P (1974) Acute toxicity of various metals to freshwater zooplankton. Bull Environ Contam Toxicol 12:745-751 598
Chan JP, Cheung MT, Li FP (1974) Trace metals in Hong Kong waters. Mar Pollut Bull 5 : 1 7 1 - 1 7 4 Chu KH, C h e u n g WM, Lau SK (1990) T r a c e m e t a l s in b i v a l v e s and s e d i m e n t s from T o l o H a r b o u r , H o n g Kong. Environ Internat 1 6 : 3 1 - 3 6 D a g g MJ (1983) A m e t h o d for the d e t e r m i n a t i o n of copepod feeding rates during short-time intervals. Mar Biol 7 5 : 6 3 - 6 7 Finney DJ (1971) Probit analysis. Cambridge University Press, London Ingersoll CG, Winner RW (1982) Effect on Daphnia pulex (De Geer) of d a i l y p u l s e e x p o s u r e s to c o p p e r or cadmium. Environ Toxicol Chem i: 321-327 Khangarot BS, Ray PK (1987) Correlation between heavy m e t a l acute t o x i c i t y v a l u e s in D a p h n i a m a q n a and fish. Bull Environ Contam Toxicol 3 8 : 7 2 2 - 7 2 6 Mance G (1987) Pollution threats of heavy metals in aquatic environments. E l s e v i e r A p p l i e d Science, New York Phillips DJH (1989) Trace metals and o r g a n o c h l o r i n e s in the c o a s t a l w a t e r s of Hong Kong. Mar P o l l u t Bull 2 0 : 3 1 9 - 3 2 7 W i n n e r RW, F a r r e l l M P (1976) A c u t e a n d c h r o n i c toxicity of copper to four species of Daphnia. J Fish Res Board Can 3 3 : 1 6 8 5 - 1 6 9 1 W o n g CK (1989) E f f e c t s of c a d m i u m on the f e e d i n g behaviour of t h e f r e s h w a t e r cladoceran Moina macrocopa. Chemosphere 1 8 : 1 6 8 1 - 1 6 8 7 Received November 20, 1991; accepted April 9, 1992.
599
i
Envirorm'mntal
Effects of Chromium, Copper, Nickel, and Zinc on Survival and Feeding of the Cladoceran Moina macrocopa C. K. Wong Department of Biology, The Chinese University of Hong Kong, Shatin, N. T., Hong Kong Heavy metals are widely recognized as highly toxic and dangerous (Mance 1987). Past research activities on h e a v y m e t a l p o l l u t i o n in Hong Kong have e m p h a s i z e d coastal environments (Chan et al. 1974; Phillips 1989; Chu et al. 1990). Since the main sources of heavy metals are the discharge and spillage of w a s t e w a t e r from electroplating factories, concentrations of heavy metals in streams and pools near industrial areas may be higher than those in coastal waters. E l e c t r o p l a t i n g wastewater in Hong Kong contains high levels of chromium, copper, nickel and zinc. The toxicity of these heavy metals to aquatic organisms has been extensively reviewed (Mance 1987). Toxicity information for invertebrates shows that crustaceans are among the most sensitive organisms (Mance 1987). Of the crustacean species tested, cladocerans appear to be the most susceptible. Cladocerans are important components of many aquatic ecosystems. Despite their importance in many freshwater communities and their sensitivity to heavy metal toxicity, information on the toxicity of heavy metals to cladocerans is limited e x c e p t for several D a p h n i a species (Biesinger and Christensen 1972; Winner and Farrell 1976; Ingersoll and W i n n e r 1982). In Hong Kong the f r e s h w a t e r cladoceran Moina macrocopa occurs in small ponds and rice paddies and is mass cultured by some farmers as a high quality fish food. The objectives of this study are to determine the effects of various heavy metals on the survival and feeding of M. macrocopa.
MATERIALS
AND
METHODS
The freshwater cladoceran Moina macrocopa came from a continuous laboratory culture raised from a single parthenogenetic female. Experiments were carried out Send reprint requests to C.K.Wong at the above address
593
w i t h c o h o r t s of n e w b o r n (< 24 hr) n e o n a t e s o b t a i n e d by isolating egg-bearing adult females from the stock culture. Stock s o l u t i o n s (i.0 g/L) of m e t a l ions w e r e p r e p a r e d by d i s s o l v i n g the m e t a l l i c salts K~Cr~O7, C u S O 4 . 5 H ~ O , NicI2.6H20 and ZnSO4.7H20 i n a i s - t i l l e d wate-r. S o l u t i o n s for a c u t e t o x i c i t y e x p e r i m e n t s a n d f e e d i n g e x p e r i m e n t s w e r e p r e p a r e d by a d d i n g a l i q u o t s of s t o c k s o l u t i o n to f i l t e r e d ( W h a t m a n GF/C) u n c o n t a m i n a t e d w a t e r from a large (300 L) aquarium. A c u t e (48 hr) l e t h a l i t y e x p e r i m e n t s w e r e c a r r i e d o u t in 50 m L b e a k e r s c o n t a i n i n g 40 m L of t e s t s o l u t i o n (pH 6.5) a n d i0 a n i m a l s . F o o d c o n s i s t e d of a m i x t u r e of the a l g a e S p i r u l i n a sp. a n d Chlorella pyrenoidosa. Food c o n c e n t r a t i o n was d e t e r m i n e d f l u o r o m e t r i c a l l y by m e a s u r i n g t h e a m o u n t of c h l o r o p h y l l _a in the water w i t h a T u r n e r M o d e l 112 f l u o r o m e t e r . Initial food concentration w a s f i x e d a t i0 u g C h l a / L b e c a u s e r e s u l t s of an e a r l i e r s t u d y (Wong 1989) s h o w e d t h a t the gut fullness of M__~. m a c r o c o p a feeding o n C__~. p y r e n o i d o s a i n c r e a s e d w i t h f o o d c o n c e n t r a t i o n up to a b o u t i0 ug c h l a / L and then r e m a i n e d unchanged. Each m e t a l ion w a s t e s t e d at 6 to 7 c o n c e n t r a t i o n s . Four r e p l i c a t e s w e r e u s e d for e a c h c o n c e n t r a t i o n . The beakers were weakly illuminated during day time by n a t u r a l light. Temperature during experiments ranged from 24 to 27 ~ C. Test s o l u t i o n s w e r e r e n e w e d after 24 h r . Newborn animals produced a t 24 h r w e r e removed. The n u m b e r of s u r v i v i n g a n i m a l s was c o u n t e d after 24 and 48 hr of exposure. Moribund animals were examined under a dissecting microscope. Individuals w i t h o u t h e a r t b e a t s w e r e c o n s i d e r e d dead. The effects of v a r i o u s m e t a l s o n feeding o f M__~. m a c r o c o p a w e r e s t u d i e d at an e x p o s u r e e q u i v a l e n t to the 48 hr LC50 of each metal. For each experiment, 20 a n i m a l s w e r e e x p o s e d in a i00 m L b e a k e r c o n t a i n i n g 60 mL of test solution. Animals maintained in u n c o n t a m i n a t e d w a t e r w e r e u s e d as controls. Four to 6 r e p l i c a t e s i n v o l v i n g a t o t a l of > i00 a n i m a l s w e r e u s e d for each metal. Food in the form of the alga C__~. p y r e n o i d o s a was i n i t i a l l y p r o v i d e d at a c o n c e n t r a t i o n of a b o u t I0 u g C h l a / L . F e e d i n g of t h e a n i m a l s w a s m e a s u r e d a f t e r 0.5, 24 and 48 hr of m e t a l e x p o s u r e . P r i o r to the s t a r t of an e x p e r i m e n t , the c o n t e n t s of the beaker were examined and dead animals were removed. Feeding experiments began when small a l i q u o t s of C__~.p y r e n o i d o s a w e r e a d d e d to the b e a k e r s to raise the food concentration t o 50 u g C h l a / L . A f t e r 15 to 20 min of feeding, animals were collected on a 0 . 1 2 5 - m m m e s h s c r e e n and i n a c t i v a t e d by freezing. Gut f u l l n e s s (chlorophyll + phaeopigments) w a s u s e d as 594
~6~
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pssodxe
RdoooIEm
"H ]o
(%) X W ~ I g W a o H
(7/6''') UO!),RJ),UeOUOO e
9 I
9 9
"I e x n S T ~
IR;al/M 7.
t, I
0 ;'0
Jq~ v 01,
I I
I
t'L
9L
Jqg~ *
~,L I
OL I
09
uz 9 i
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- og -OOL
I' ~~-o v
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chromium > zinc > n i c k e l has b e e n r e p o r t e d for D a p h n i a h y a l i n a (Baudouin and S c o p p a 1974). P r o b i t a n a l y s i s (Finney 1971) i n d i c a t e d t h a t c o p p e r was c l e a r l y m o r e t o x i c to M_~. m a c r o c o p a t h a n the other m e t a l s (Table i). T h e 24 and 48 h r L C 5 0 v a l u e s for c o p p e r w e r e one to s e v e r a l o r d e r s of m a g n i t u d e l o w e r t h a n t h o s e for the o t h e r m e t a l s . For copper, t h e r e was only a slight difference between t h e 24 h r L C 5 0 and 48 hr LC50. For the other metals, the 48 hr LC50 w a s l o w e r t h a n t h e 24 h r LC50. The difference was about twofold for chromium and zinc, and close to f o u r f o l d for nickel. T h e s e r e s u l t s d e m o n s t r a t e d that t h e r e was an increase in t o x i c i t y f o l l o w i n g p r o l o n g e d exposure. The order of both LC50 v a l u e s was n i c k e l > zinc > c h r o m i u m > copper.
T a b l e i. LCS0 v a l u e s (mg/L) of chromium, copper, nickel and zinc for M__=. m a c r o c o p a . 95% c o n f i d e n c e limits are i n d i c a t e d in p a r e n t h e s e s .
24 hr
48 hr
Cr
0.76
(0.69-0.83)
0.36
(0.29-0.40)
Cu
0.09
(0.08-0.10)
0.08
(0.07-0.09)
Ni
23.59
(12.99-34.19)
6.48
(5.55-7.41)
Zn
2.04
(1.75-2.33)
1.17
(1.02-1.32)
596
200
Cr 150
100
50
I
0
I
200
Cu
15o
100
0k .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
50
~
1 0
0
0
20O
I
Ni
ql,-.
0
I
'
150
100
................................
~ ................................
200
Zn
160
100
50
I
I
24
4B
Time (hr) F i g u r e 2. Gut f u l l n e s s of M. m a c r o c o p a a f t e r 0.5, 24 and 48 hr of e x p o s u r e to chromium, copper, n i c k e l and zinc at a c o n c e n t r a t i o n e q u i v a l e n t to t h e 48 hr LC50 of e a c h metal. Gut f u l l n e s s of c o n t r o l a n i m a l s is expressed as 100%. Each point represents the mean and range of 6 t o i0 fluorometer counts u s i n g a t o t a l of at least 60 animals.
597
C o m p a r i s o n a m o n g species is a p p r o x i m a t e because many e x p e r i m e n t a l v a r i a b l e s m a y a f f e c t toxicity. In t e r m s of L C 5 0 v a l u e s , M_~. m a c r o c o p a w a s l e s s s e n s i t i v e t o h e a v y m e t a l s than some of the D a p h n i a species. The 48 hr L C 5 0 of 0.08 m g C u / L for M__~.m a c r o c o p a w a s s i m i l a r to those reported f o r D__~.m a q n a (Biesinger and C h r i s t e n s e n 1972, K h a n g a r o t and R a y 1987) a n d h i g h e r t h a n t h o s e r e p o r t e d for D__~.p u l e x (Ingersoll and W i n n e r 1982) and D__~.h y a l i n a (Baudouin and Scoppa 1974). For c h r o m i u m , n i c k e l and zinc, 48 hr L C 5 0 v a l u e s for M_~. macrocopa were m u c h h i g h e r than t h o s e for D~. h y a l i n a (Baudouin and S c o p p a 1974). The f e e d i n g of M__~.m a c r o c o p a was m e a s u r e d a f t e r 0.5, 24 a n d 48 h r of e x p o s u r e to m e t a l s at concentrations equivalent t o t h e 48 h r L C 5 0 v a l u e of e a c h m e t a l (Figure 2). Gut fullness of a n i m a l s e x p o s e d to m e t a l s was e x p r e s s e d as a p e r c e n t a g e of the control. R e s u l t s were tested with 2 - w a y A N O V A w i t h e x p o s u r e t i m e and p r e s e n c e o r a b s e n c e of m e t a l as t h e m a i n f a c t o r s . V a r i a b i l i t y in gut fullness was h i g h a m o n g replicates. A s i g n i f i c a n t e f f e c t (P < 0.05) of m e t a l s w a s n o t e d for copper, c h r o m i u m and nickel, w h e r e a s s i g n i f i c a n t effects (P < 0.05) of e x p o s u r e t i m e w a s n o t e d f o r c o p p e r , c h r o m i u m a n d zinc. For all four metals, t h e r e was no e v i d e n c e of i n t e r a c t i o n b e t w e e n the m a i n factors. Animals exposed to c o p p e r for just 0.5 hr showed a 65 % r e d u c t i o n in gut fullness. A t 24 hr, gut fullness was depressed b y m o r e t h a n 50 % in a n i m a l s e x p o s e d to chromium, c o p p e r and nickel, and by a b o u t 30 % in a n i m a l s e x p o s e d to zinc. A c o n t i n u e d , but less pronounced, i n h i b i t o r y e f f e c t was o b s e r v e d at 48 hr. Gut fullness of s u r v i v i n g animals was r e d u c e d by a b o u t 58% in chromium, 77% in nickel, 42 % in z i n c a n d o n l y 14% in c o p p e r . Decreased food intake leads to lower r e p r o d u c t i v e c a p a c i t y which, in turn, may reduce population size. These results s u g g e s t e d that feeding is a u s e f u l i n d i c a t o r of m e t a l exposure.
Acknowledgments. The a u t h o r t h a n k s Ms. S.W. Hui for her h e l p in p e r f o r m i n g the experiments. This w o r k was supported by a grant from the Croucher Foundation, H o n g Kong. REFERENCES B i e s i n g e r KE, c h r i s t e n s e n GM (1972) E f f e c t s of v a r i o u s metals on survival, growth, reproduction, and m e t a b o l i s m of D a p h n i a maqna. J Fish Res Bd Can 29: 1691-1700 Baudouin MF, Scoppa P (1974) Acute toxicity of various metals to freshwater zooplankton. Bull Environ Contam Toxicol 12:745-751 598
Chan JP, Cheung MT, Li FP (1974) Trace metals in Hong Kong waters. Mar Pollut Bull 5 : 1 7 1 - 1 7 4 Chu KH, C h e u n g WM, Lau SK (1990) T r a c e m e t a l s in b i v a l v e s and s e d i m e n t s from T o l o H a r b o u r , H o n g Kong. Environ Internat 1 6 : 3 1 - 3 6 D a g g MJ (1983) A m e t h o d for the d e t e r m i n a t i o n of copepod feeding rates during short-time intervals. Mar Biol 7 5 : 6 3 - 6 7 Finney DJ (1971) Probit analysis. Cambridge University Press, London Ingersoll CG, Winner RW (1982) Effect on Daphnia pulex (De Geer) of d a i l y p u l s e e x p o s u r e s to c o p p e r or cadmium. Environ Toxicol Chem i: 321-327 Khangarot BS, Ray PK (1987) Correlation between heavy m e t a l acute t o x i c i t y v a l u e s in D a p h n i a m a q n a and fish. Bull Environ Contam Toxicol 3 8 : 7 2 2 - 7 2 6 Mance G (1987) Pollution threats of heavy metals in aquatic environments. E l s e v i e r A p p l i e d Science, New York Phillips DJH (1989) Trace metals and o r g a n o c h l o r i n e s in the c o a s t a l w a t e r s of Hong Kong. Mar P o l l u t Bull 2 0 : 3 1 9 - 3 2 7 W i n n e r RW, F a r r e l l M P (1976) A c u t e a n d c h r o n i c toxicity of copper to four species of Daphnia. J Fish Res Board Can 3 3 : 1 6 8 5 - 1 6 9 1 W o n g CK (1989) E f f e c t s of c a d m i u m on the f e e d i n g behaviour of t h e f r e s h w a t e r cladoceran Moina macrocopa. Chemosphere 1 8 : 1 6 8 1 - 1 6 8 7 Received November 20, 1991; accepted April 9, 1992.
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