Arch. Environm. Contain. Toxicol. 8, 279-283 (1979)
Archivesof
Environmental Contamination and Toxicology
Effect of Selenium Dioxide on the Accumulation and Acute Toxicity of Mercuric Chloride in Goldfish J. F. Heisinger, C. D. Hansen and Jong Hwan Kim BiologyDepartment, Universityof South Dakota, Vermillion, SD 57069
Abstract. Acute toxicity tests showed that selenium dioxide was a strong antagonist against mercuric chloride toxicity in goldfish. Paradoxically, whole body accumulations of total mercury were found to be significantly increased with the administration of Se. Maximum binding of Hg to fish was produced by approximately equimolar experimental concentrations of Hg and Se, but higher levels of Se reduced this binding. The greater the Hg accumulation the greater was the ability to survive a given environmental Hg concentration. Much of the Hg was in the skin and surface mucus on the gills and body; however, Se also increased Hg concentration in the inner tissues of the fish. Parizek and Ostadalova (1967) were the first to demonstrate that inorganic Se greatly reduced the acute toxicity of mercuric chloride. Ganther et al. (1972) discovered that Hg and Se were being accumulated in an approximate 1:1 molar ratio in tuna. Despite their high Hg concentrations, tuna added to the methylmercury treated foods of Japanese quail and rats protected these animals. Subsequent numerous studies have verified this protective interaction between Hg and Se in mammals and birds. This implies that the danger for man of Hg in fish (i.e., tuna) may be somewhat less than anticipated. However, knowledge concerning Hg and Se protective interactions in fish is sparse and somewhat contradictory. Huckabee and Griffith (1974) found, paradoxically, that Se and Hg mixtures were more toxic to carp eggs than Hg alone; but K i m et al. (1977) found Se to be protective against mercuric chloride in adult northern creek chubs. This discrepancy might be due to differences in life stages tested. Huckabee and Griffith's report of a protective failure between Hg and Se is not unique. Kasuya (1976) suggested that the adverse effect of Se at high concentrations is additive to the toxicity of methylmercuric chloride in cultured nervous tissue. The specific objectives of this study were: (1) to ascertain if Se protected goldfish against inorganic Hg toxicity; (2) to compare any disparity of Se pretreatment with Se administered simultaneously with Hg; (3) to rneasure any differences in Hg accumulation between Hg only treatments and those with both Hg and Se treatments.
0090-4341/79/0008-0279 $01.00 O 1979 Springer-Verlag New York Inc.
280
J.F. Heisinger et al.
Materials and Methods Goldfish (Carassius auratus) were purchased from a local supplier and kept without mortality for at least one week prior to the experimental procedure. They were fed Tetra Min,| a high protein diet. The fish specimens ranged in length from 4.5 to 6.5 cm and were sorted at random into groups of twenty. Each group of fish was placed in approximately 24 liters of demineralized water (about 1,000,000 ohms/cm at 25~ to which 100 mg/L of CaCOa and the various test substances were added. Experimental water temperature was maintained at 24 to 25~ and the aquaria were oxygenated and lined with polyethylene sheets. Toxicity test substances used were mercuric chloride (HgC12) and selenium dioxide (SeO2). Four simultaneous experimental sets were initiated. All of the fish were subjected to the same concentrations of Hg (0.18, 0.24, 0.32, 0.42 and 0.56 mg/L). In experimental set A, the five groups (consisting of twenty fish per group) were subjected to Hg only, one group to each concentration. In set B 0.5 mg/L Se was given simultaneously with the Hg. Experimental set C consisted of the five groups which received the various Hg concentrations with a simultaneous equimolar concentration of Se. Fish in set D were treated with equimolar Se:Hg but received the Se as a pretreatment (48 hr). Throughout the entire four days of experimentation none of the control fish died. The fish were exposed to the test substances for 48 hr with eight hr interval checks for mortality. Food was withheld during pretreatment and test periods. Survivors were collected at the termination of the testing periods and frozen for future mercury analysis. Later, they were dried to a constant weight at 100~ An experiment was performed to test for Hg loss from the fish through volatilization during dehydration; ten fish were paired by weight and subjected for 48 hr to a solution containing 0.1 mg/L Hg. The fish were then frozen, but five were subsequently dehydrated at 100~ The Hg concentration (mean and standard error) of the heattreated group was 4.29 - 0.42/xg/g wet weight. The unheated group contained 4.09 +--0.42 ~g/g wet weight. No evidence of Hg loss was observed. Eight untreated goldfish were tested for background Hg concentrations. Considerable variation was found, but all contained less than 0.2/zg/g wet weight. An additional experiment, to determine the sites of the Hg in the fish, was performed on the portions of sets A and B which had been treated with 0.32 mg/L Hg. The fish were divided into three compartments; the unskinned head and gills, muscle-viscera, and the body skin. Fish were digested in a mixture of nitric and sulfuric acid with vanadium pentoxide as a catalyst (Deitz et al. 1973); and a Perkin-Elmer Model 360 Atomic Absorption Spectrophotometer was used for Hg analysis. The concentration-percent mortality data were analyzed with a logarithmic-probability (logprobit) program (Dixon 1973) on an IBM 370 computer. Confidence limits for the LCs0 values were derived as described by Cardwell et al. (1976).
Results and Discussion T h e c u m u l a t i v e p e r c e n t m o r t a l i t y o f t h e A g r o u p s ( H g only) i n c r e a s e d rapidly as t h e H g in t h e w a t e r i n c r e a s e d ( F i g u r e 1). T h e a d d i t i o n o f s e l e n i u m d i o x i d e d e c r e a s e d t h e c o m p a r a t i v e p e r c e n t m o r ta li ti e s (sets B, C a n d D) at the v a r i o u s H g c o n c e n t r a t i o n s . T h e m e d i a n lethal c o n c e n t r a t i o n (LCs0) w a s e m p l o y e d to e x p r e s s t h e s e d i f f e r e n c e s in s u r v i v a l ( T a b l e 1). N o n e o f the 95% c o n f i d e n c e limits o f t h e c a l c u l a t e d LCs0s f o r t h e t h r e e s e l e n i u m - t r e a t e d e x p e r i m e n t a l sets o v e r l a p p e d t h a t o f t h e a n i m a l s t r e a t e d o n l y w i t h H g . K i m e t al. (1977) r e p o r t e d similar results; t h e 48-hr LCs0 o f Se p r e t r e a t e d n o r t h e r n c r e e k c h u b s was m u c h h i g h e r (LCso = 0.20 m g / L ) t h a n t h a t o f the H g o n l y g r o u p (LCs0 = 0.10). T h e g r e a t e s t p r o t e c t i o n w a s c o n f e r r e d o n set D, w h i c h w a s g i v e n e q u i m o l a r Se as a 48-hr p r e t r e a t m e n t . S e t B (0.5 p p m selenium) had e s s e n t i a l l y t h e s a m e LCso as set C ( Hg e q u i m o l a r w i t h Se). F i s h t a k e up i n o rg an i c S e s l o w l y ( S a n d h o l m e t al.
Effect of Selenium Dioxide on the Accumulation and Acute Toxicity of Mercury in Goldfish
>..
O
Ioo
A=
9
Hg only
B =
9
Hg=~ Se (0.5mg/L)
A~...~ ~
C ....
~ - - - - - - Hg = Se (equimolar)
D ....
D - - - - - - Hg= Se given as a pretreatment
>
B//.
~ 9 ~
9
//// /
/
//C //2"
~
"c _
O //.
68
//U/
w
281
40
9
/
9
/ / /
/
O/
--d 20 9
O
-71/
.18
24
y."
f/
.32
.42
.56
MERCURY CONCENTRATION (mg/L) Fig. 1. The cumulative percent mortality of goldfish subjected to various concentrations of HgC12 with Se treatments administered to sets B, C and D. Twenty animals were utilized in each set at each concentration.
1973); the pretreated animals obviously had more time to absorb the Se and to allow protective metabolic alterations to occur. Selenium has been shown to increase the retention of Hg in many animals, and we wished to determine if Se promoted high concentrations of Hg in goldfish. All experimental groups had similar whole body mercury concentrations at 0.18 mg/L (Table 2). Selenium-treated survivors, at the four other tested concentrations, always had higher average Hg concentrations. Despite the high body burdens in the B, C and D sets, survival was much better than in group A. When the body concentrations of Hg for all of the experimental sets (A through D) were correlated with the experimental Hg concentrations, the correlation coefficient was statistically significant (r = 0.4444, P < 0.001). Mercury is taken up directly (no food chain required) from the water by goldfish (McKone et aI. 1971; Kim et al. 1977), and the dry-weight body concentrations reported herein are similar to those reported by McKone. Mercury was approximately 65 Table 1. Calculated LC~0s with 95% confidence limits Confidence limits Set
Treatment
A B C D
Hg only Hg ~ Se (0:5 mg/L) Hg = Se (equimolar) Hg = Se (equimolar but Se as a pretreatment)
LCso Hg mg/L
lower
upper
.35 .43 .44
.33 .40 .39
.38 .47 .50
.50
.44
.56
J . F . Heisinger et al.
282
Table 2. Mean a (_ std. error of the mean) whole body mercury concentrations (/~g/g dry weight) Hg
treatment mg/L 0.18 0.24 0.32 0.42
A Hg only
B Hg ~ Se 0.5 mg/L
C Hg = Se equimolar
D Hg = Se pretreatment
30.78 22.27 22.16 Nb = 27.83 N=0
29.94 _+ 2.72 34.00 + 4.07 29.39 _+ 6.62
28.68 -+ 1.75 52.96 -+ 3.41 35.04 -+ 5.40
28.27 - 1.27 52.04 +_ 6.56 61.99 -+ 3.71
40.01 _+ 4.34 N=0
62.49 +- 3.21 N=2 78.23 +- 20.44
46.03 _+ 5.83
_+ 1 . 1 1 _+ 3.81 -+ 1.75 3 -- 3.67
0.56
50.02 -+ 10.31
a Means derived from four animals unless otherwise stated b N = the number in each exception
times more concentrated in the fish than in the experimental solutions [Y = 19.53 + (64.95 9 X)]. However, the quantitative aspects of this phenomenon are noticeably different between Se-treated and untreated fish (Table 2). The Hgtreated fish did not survive at Hg body accumulations above 35/xg/g dry weight (range of survivors 12 to 35 ~g/g). The Se-treated fish survived at Hg body concentrations in the range of 19 to 98/zg/g. Experimental concentrations of Se greater than equimolar (set B) depressed Hg tissue concentrations and may have slightly decreased survival. Preliminary studies indicated that 0.5 mg/L of Se was not lethal in a short term experiment. Fish treated with Hg only (A) displayed no significant differences among compartments (Table 3). However, the fish pretreated with Se in Group D did not exhibit a uniform Hg concentration among compartments but, instead, an altered distribution, with the head showing significantly higher (Student's t-test) amounts of Hg than muscle-viscera or body skin (P < .05). Perhaps much of the head compartment mercury in our study was in the mucus on the gills and head skin.
Table 3. Comparison of mean (-+ std. error) distributions among three experimental compartments of fish from Set A (Hg only) and D (pretreated with Se). Each mean represents samples subjected to 0.32 mg/L Hg a UnsMnnedhead
Muscle-viscera
BodysNn
Hg ~gb
Hg ~g
Hg ~g
33.02 1.13
33.49 10.60
26.18 3.45
74.35 8.17
41.35 8.08
41.72 3.19
Set A JK S~
Set D Sf~
a Four fish were analyzed from each treatment set b Dry weight
Effect of Selenium Dioxide on the Accumulation and Acute Toxicity of Mercury in Goldfish
283
Metals, such as lead and mercury, stimulate mucus secretion and accumulate in the mucus. McKone et al. (1971) found that 79.3% of the total mercury in mercuric chloride-treated goldfish was in the surface mucus. We noted that Se also promoted a copious mucus coat on the gills and skin. Fish pretreated with Se would be predisposed to collect large quantities of Hg on their mucusqaden surfaces. However, the muscle-viscera compartment (without skin) of the Setreated fish also contained more Hg than the animals treated with Hg only (Table 3). This is consistent with data on other vertebrates. Selenium may promote a differential distribution of Hg between the various internal organs. The redistribution of Hg following a Se injection in rats was discussed by Burk et al. (1974). They suggested that detoxication of mercury by inorganic Se compounds probably resulted from an alteration of tissue binding of mercury within the organism. In Se-treated rats, the retention of inorganic Hg was markedly increased in the blood, liver and spleen but reduced in the kidney (Moffit and Clary 1974; Potter and Matrone 1974). These invesitgations suggest that the elimination of Hg from the kidney may produce the protection mechanism. Obviously experiments of longer duration with larger fish and subsequent organ analysis will need to be performed before the question of alteration of Hgbinding by Se-treated fish can be resolved.
References Burk, R. F., K. A. Foster, P. M. Greenfield, and K. W. Kiker: Binding of simultaneously administered inorganic selenium and mercury to a rat plasma protein. Proc. Soc. Exp. Biol. Med. 145, 782 (1974). Cardwell, R. D., D. G. Goreman, T. R. Payne, and D. J. Wilbur: Acute toxicity of selenium dioxide to freshwater fishes. Arch. Environ. Contam. Toxicol. 4, 129 (1976). Deitz, F. D., J. L. Sell, and D. Bristol: Rapid sensitive method for determination of mercury in a variety of biological samples. J. Assoc. Offic. Anal. Chem. 56,378 (1973). Dixon, W. J. (ed.): BMD; biomedical computer programs. 3rd ed. Berkeley: University of California Press (1973). Ganther, H. E., C. Goudie, M. L. Sunde, M. J. Kopecky, P. Wagner, S. Oh, and W. G. Hockstra: Selenium: Relation to decreased toxicity of methylmercury added to diets containing tuna. Science 175, 1122 (1972). Huckabee, J. W., and N. A. Griffith: Toxicity of mercury and selenium to the eggs of carp (Cyprinus carpio). Trans. Amer. Fish. Soc. 4, 822 (1974). Kasuya, M.: Effect of selenium on the toxicity of methylmercury on nervous tissue in culture. Toxicol. Appt. Pharmacol. 35, 11 (1976). Kim, J. H., E. Birks, and J. F. Heisinger: Protective action of selenium against mercury in northern creek chubs. Bull. Environ. Contam. Toxicol. 17, 132 (1977). McKone, C., R. G. Young, C. A. Bache, and D. J. Lisk: Rapid uptake of mercuric ion by goldfish. Environ. Sci. Techol. 5, 1139 (1971). Moffitt, A. E., and J. J. Clary: Selenite-induced binding of inorganic mercury in blood and other tissues in the rat. Res. Commun. Chem. Pathol. Pharmacol. 7, 593 (1974). Parizek, J., and I. Ostadalova: The protective effect of small amounts of selenite in sublimate intoxication. Experientia 23, 142 (1967). Potter, S., and G. Matrone: Effect of selenite on the toxicity of dietary methylmercury and mercuric chloride in the rat. J. of Nutr. 104, 638 (1974). Sandholm, M., H. E. Oksanen, and L. Pesonen: Uptake of selenium by aquatic organisms. Limnol. Oceanogr. 18,496 (1973).
Manuscript received December 12, 1977; accepted July 22, 1978.
Archivesof
Environmental Contamination and Toxicology
Effect of Selenium Dioxide on the Accumulation and Acute Toxicity of Mercuric Chloride in Goldfish J. F. Heisinger, C. D. Hansen and Jong Hwan Kim BiologyDepartment, Universityof South Dakota, Vermillion, SD 57069
Abstract. Acute toxicity tests showed that selenium dioxide was a strong antagonist against mercuric chloride toxicity in goldfish. Paradoxically, whole body accumulations of total mercury were found to be significantly increased with the administration of Se. Maximum binding of Hg to fish was produced by approximately equimolar experimental concentrations of Hg and Se, but higher levels of Se reduced this binding. The greater the Hg accumulation the greater was the ability to survive a given environmental Hg concentration. Much of the Hg was in the skin and surface mucus on the gills and body; however, Se also increased Hg concentration in the inner tissues of the fish. Parizek and Ostadalova (1967) were the first to demonstrate that inorganic Se greatly reduced the acute toxicity of mercuric chloride. Ganther et al. (1972) discovered that Hg and Se were being accumulated in an approximate 1:1 molar ratio in tuna. Despite their high Hg concentrations, tuna added to the methylmercury treated foods of Japanese quail and rats protected these animals. Subsequent numerous studies have verified this protective interaction between Hg and Se in mammals and birds. This implies that the danger for man of Hg in fish (i.e., tuna) may be somewhat less than anticipated. However, knowledge concerning Hg and Se protective interactions in fish is sparse and somewhat contradictory. Huckabee and Griffith (1974) found, paradoxically, that Se and Hg mixtures were more toxic to carp eggs than Hg alone; but K i m et al. (1977) found Se to be protective against mercuric chloride in adult northern creek chubs. This discrepancy might be due to differences in life stages tested. Huckabee and Griffith's report of a protective failure between Hg and Se is not unique. Kasuya (1976) suggested that the adverse effect of Se at high concentrations is additive to the toxicity of methylmercuric chloride in cultured nervous tissue. The specific objectives of this study were: (1) to ascertain if Se protected goldfish against inorganic Hg toxicity; (2) to compare any disparity of Se pretreatment with Se administered simultaneously with Hg; (3) to rneasure any differences in Hg accumulation between Hg only treatments and those with both Hg and Se treatments.
0090-4341/79/0008-0279 $01.00 O 1979 Springer-Verlag New York Inc.
280
J.F. Heisinger et al.
Materials and Methods Goldfish (Carassius auratus) were purchased from a local supplier and kept without mortality for at least one week prior to the experimental procedure. They were fed Tetra Min,| a high protein diet. The fish specimens ranged in length from 4.5 to 6.5 cm and were sorted at random into groups of twenty. Each group of fish was placed in approximately 24 liters of demineralized water (about 1,000,000 ohms/cm at 25~ to which 100 mg/L of CaCOa and the various test substances were added. Experimental water temperature was maintained at 24 to 25~ and the aquaria were oxygenated and lined with polyethylene sheets. Toxicity test substances used were mercuric chloride (HgC12) and selenium dioxide (SeO2). Four simultaneous experimental sets were initiated. All of the fish were subjected to the same concentrations of Hg (0.18, 0.24, 0.32, 0.42 and 0.56 mg/L). In experimental set A, the five groups (consisting of twenty fish per group) were subjected to Hg only, one group to each concentration. In set B 0.5 mg/L Se was given simultaneously with the Hg. Experimental set C consisted of the five groups which received the various Hg concentrations with a simultaneous equimolar concentration of Se. Fish in set D were treated with equimolar Se:Hg but received the Se as a pretreatment (48 hr). Throughout the entire four days of experimentation none of the control fish died. The fish were exposed to the test substances for 48 hr with eight hr interval checks for mortality. Food was withheld during pretreatment and test periods. Survivors were collected at the termination of the testing periods and frozen for future mercury analysis. Later, they were dried to a constant weight at 100~ An experiment was performed to test for Hg loss from the fish through volatilization during dehydration; ten fish were paired by weight and subjected for 48 hr to a solution containing 0.1 mg/L Hg. The fish were then frozen, but five were subsequently dehydrated at 100~ The Hg concentration (mean and standard error) of the heattreated group was 4.29 - 0.42/xg/g wet weight. The unheated group contained 4.09 +--0.42 ~g/g wet weight. No evidence of Hg loss was observed. Eight untreated goldfish were tested for background Hg concentrations. Considerable variation was found, but all contained less than 0.2/zg/g wet weight. An additional experiment, to determine the sites of the Hg in the fish, was performed on the portions of sets A and B which had been treated with 0.32 mg/L Hg. The fish were divided into three compartments; the unskinned head and gills, muscle-viscera, and the body skin. Fish were digested in a mixture of nitric and sulfuric acid with vanadium pentoxide as a catalyst (Deitz et al. 1973); and a Perkin-Elmer Model 360 Atomic Absorption Spectrophotometer was used for Hg analysis. The concentration-percent mortality data were analyzed with a logarithmic-probability (logprobit) program (Dixon 1973) on an IBM 370 computer. Confidence limits for the LCs0 values were derived as described by Cardwell et al. (1976).
Results and Discussion T h e c u m u l a t i v e p e r c e n t m o r t a l i t y o f t h e A g r o u p s ( H g only) i n c r e a s e d rapidly as t h e H g in t h e w a t e r i n c r e a s e d ( F i g u r e 1). T h e a d d i t i o n o f s e l e n i u m d i o x i d e d e c r e a s e d t h e c o m p a r a t i v e p e r c e n t m o r ta li ti e s (sets B, C a n d D) at the v a r i o u s H g c o n c e n t r a t i o n s . T h e m e d i a n lethal c o n c e n t r a t i o n (LCs0) w a s e m p l o y e d to e x p r e s s t h e s e d i f f e r e n c e s in s u r v i v a l ( T a b l e 1). N o n e o f the 95% c o n f i d e n c e limits o f t h e c a l c u l a t e d LCs0s f o r t h e t h r e e s e l e n i u m - t r e a t e d e x p e r i m e n t a l sets o v e r l a p p e d t h a t o f t h e a n i m a l s t r e a t e d o n l y w i t h H g . K i m e t al. (1977) r e p o r t e d similar results; t h e 48-hr LCs0 o f Se p r e t r e a t e d n o r t h e r n c r e e k c h u b s was m u c h h i g h e r (LCso = 0.20 m g / L ) t h a n t h a t o f the H g o n l y g r o u p (LCs0 = 0.10). T h e g r e a t e s t p r o t e c t i o n w a s c o n f e r r e d o n set D, w h i c h w a s g i v e n e q u i m o l a r Se as a 48-hr p r e t r e a t m e n t . S e t B (0.5 p p m selenium) had e s s e n t i a l l y t h e s a m e LCso as set C ( Hg e q u i m o l a r w i t h Se). F i s h t a k e up i n o rg an i c S e s l o w l y ( S a n d h o l m e t al.
Effect of Selenium Dioxide on the Accumulation and Acute Toxicity of Mercury in Goldfish
>..
O
Ioo
A=
9
Hg only
B =
9
Hg=~ Se (0.5mg/L)
A~...~ ~
C ....
~ - - - - - - Hg = Se (equimolar)
D ....
D - - - - - - Hg= Se given as a pretreatment
>
B//.
~ 9 ~
9
//// /
/
//C //2"
~
"c _
O //.
68
//U/
w
281
40
9
/
9
/ / /
/
O/
--d 20 9
O
-71/
.18
24
y."
f/
.32
.42
.56
MERCURY CONCENTRATION (mg/L) Fig. 1. The cumulative percent mortality of goldfish subjected to various concentrations of HgC12 with Se treatments administered to sets B, C and D. Twenty animals were utilized in each set at each concentration.
1973); the pretreated animals obviously had more time to absorb the Se and to allow protective metabolic alterations to occur. Selenium has been shown to increase the retention of Hg in many animals, and we wished to determine if Se promoted high concentrations of Hg in goldfish. All experimental groups had similar whole body mercury concentrations at 0.18 mg/L (Table 2). Selenium-treated survivors, at the four other tested concentrations, always had higher average Hg concentrations. Despite the high body burdens in the B, C and D sets, survival was much better than in group A. When the body concentrations of Hg for all of the experimental sets (A through D) were correlated with the experimental Hg concentrations, the correlation coefficient was statistically significant (r = 0.4444, P < 0.001). Mercury is taken up directly (no food chain required) from the water by goldfish (McKone et aI. 1971; Kim et al. 1977), and the dry-weight body concentrations reported herein are similar to those reported by McKone. Mercury was approximately 65 Table 1. Calculated LC~0s with 95% confidence limits Confidence limits Set
Treatment
A B C D
Hg only Hg ~ Se (0:5 mg/L) Hg = Se (equimolar) Hg = Se (equimolar but Se as a pretreatment)
LCso Hg mg/L
lower
upper
.35 .43 .44
.33 .40 .39
.38 .47 .50
.50
.44
.56
J . F . Heisinger et al.
282
Table 2. Mean a (_ std. error of the mean) whole body mercury concentrations (/~g/g dry weight) Hg
treatment mg/L 0.18 0.24 0.32 0.42
A Hg only
B Hg ~ Se 0.5 mg/L
C Hg = Se equimolar
D Hg = Se pretreatment
30.78 22.27 22.16 Nb = 27.83 N=0
29.94 _+ 2.72 34.00 + 4.07 29.39 _+ 6.62
28.68 -+ 1.75 52.96 -+ 3.41 35.04 -+ 5.40
28.27 - 1.27 52.04 +_ 6.56 61.99 -+ 3.71
40.01 _+ 4.34 N=0
62.49 +- 3.21 N=2 78.23 +- 20.44
46.03 _+ 5.83
_+ 1 . 1 1 _+ 3.81 -+ 1.75 3 -- 3.67
0.56
50.02 -+ 10.31
a Means derived from four animals unless otherwise stated b N = the number in each exception
times more concentrated in the fish than in the experimental solutions [Y = 19.53 + (64.95 9 X)]. However, the quantitative aspects of this phenomenon are noticeably different between Se-treated and untreated fish (Table 2). The Hgtreated fish did not survive at Hg body accumulations above 35/xg/g dry weight (range of survivors 12 to 35 ~g/g). The Se-treated fish survived at Hg body concentrations in the range of 19 to 98/zg/g. Experimental concentrations of Se greater than equimolar (set B) depressed Hg tissue concentrations and may have slightly decreased survival. Preliminary studies indicated that 0.5 mg/L of Se was not lethal in a short term experiment. Fish treated with Hg only (A) displayed no significant differences among compartments (Table 3). However, the fish pretreated with Se in Group D did not exhibit a uniform Hg concentration among compartments but, instead, an altered distribution, with the head showing significantly higher (Student's t-test) amounts of Hg than muscle-viscera or body skin (P < .05). Perhaps much of the head compartment mercury in our study was in the mucus on the gills and head skin.
Table 3. Comparison of mean (-+ std. error) distributions among three experimental compartments of fish from Set A (Hg only) and D (pretreated with Se). Each mean represents samples subjected to 0.32 mg/L Hg a UnsMnnedhead
Muscle-viscera
BodysNn
Hg ~gb
Hg ~g
Hg ~g
33.02 1.13
33.49 10.60
26.18 3.45
74.35 8.17
41.35 8.08
41.72 3.19
Set A JK S~
Set D Sf~
a Four fish were analyzed from each treatment set b Dry weight
Effect of Selenium Dioxide on the Accumulation and Acute Toxicity of Mercury in Goldfish
283
Metals, such as lead and mercury, stimulate mucus secretion and accumulate in the mucus. McKone et al. (1971) found that 79.3% of the total mercury in mercuric chloride-treated goldfish was in the surface mucus. We noted that Se also promoted a copious mucus coat on the gills and skin. Fish pretreated with Se would be predisposed to collect large quantities of Hg on their mucusqaden surfaces. However, the muscle-viscera compartment (without skin) of the Setreated fish also contained more Hg than the animals treated with Hg only (Table 3). This is consistent with data on other vertebrates. Selenium may promote a differential distribution of Hg between the various internal organs. The redistribution of Hg following a Se injection in rats was discussed by Burk et al. (1974). They suggested that detoxication of mercury by inorganic Se compounds probably resulted from an alteration of tissue binding of mercury within the organism. In Se-treated rats, the retention of inorganic Hg was markedly increased in the blood, liver and spleen but reduced in the kidney (Moffit and Clary 1974; Potter and Matrone 1974). These invesitgations suggest that the elimination of Hg from the kidney may produce the protection mechanism. Obviously experiments of longer duration with larger fish and subsequent organ analysis will need to be performed before the question of alteration of Hgbinding by Se-treated fish can be resolved.
References Burk, R. F., K. A. Foster, P. M. Greenfield, and K. W. Kiker: Binding of simultaneously administered inorganic selenium and mercury to a rat plasma protein. Proc. Soc. Exp. Biol. Med. 145, 782 (1974). Cardwell, R. D., D. G. Goreman, T. R. Payne, and D. J. Wilbur: Acute toxicity of selenium dioxide to freshwater fishes. Arch. Environ. Contam. Toxicol. 4, 129 (1976). Deitz, F. D., J. L. Sell, and D. Bristol: Rapid sensitive method for determination of mercury in a variety of biological samples. J. Assoc. Offic. Anal. Chem. 56,378 (1973). Dixon, W. J. (ed.): BMD; biomedical computer programs. 3rd ed. Berkeley: University of California Press (1973). Ganther, H. E., C. Goudie, M. L. Sunde, M. J. Kopecky, P. Wagner, S. Oh, and W. G. Hockstra: Selenium: Relation to decreased toxicity of methylmercury added to diets containing tuna. Science 175, 1122 (1972). Huckabee, J. W., and N. A. Griffith: Toxicity of mercury and selenium to the eggs of carp (Cyprinus carpio). Trans. Amer. Fish. Soc. 4, 822 (1974). Kasuya, M.: Effect of selenium on the toxicity of methylmercury on nervous tissue in culture. Toxicol. Appt. Pharmacol. 35, 11 (1976). Kim, J. H., E. Birks, and J. F. Heisinger: Protective action of selenium against mercury in northern creek chubs. Bull. Environ. Contam. Toxicol. 17, 132 (1977). McKone, C., R. G. Young, C. A. Bache, and D. J. Lisk: Rapid uptake of mercuric ion by goldfish. Environ. Sci. Techol. 5, 1139 (1971). Moffitt, A. E., and J. J. Clary: Selenite-induced binding of inorganic mercury in blood and other tissues in the rat. Res. Commun. Chem. Pathol. Pharmacol. 7, 593 (1974). Parizek, J., and I. Ostadalova: The protective effect of small amounts of selenite in sublimate intoxication. Experientia 23, 142 (1967). Potter, S., and G. Matrone: Effect of selenite on the toxicity of dietary methylmercury and mercuric chloride in the rat. J. of Nutr. 104, 638 (1974). Sandholm, M., H. E. Oksanen, and L. Pesonen: Uptake of selenium by aquatic organisms. Limnol. Oceanogr. 18,496 (1973).
Manuscript received December 12, 1977; accepted July 22, 1978.
