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Determination of mercury in fish from rivers and lakes in Hungary by atomic absorption technique
Toxicology, 7 (1977) 349--355 © Elsevier/North-Holland Scientific Publishers, Ltd.
DETERMINATION OF MERCURY IN FISH FROM RIVERS AND LAKES IN HUNGARY BY ATOMIC ABSORPTION TECHNIQUE
ANNA GERGELY, KATALIN SO(~S, L/kSZL6 ERDELYI and VILMOS CIELESZKY Institute of Nutrition, 1097 Budapest Gy6li ut 3/a (Hungary)
(Received September 14th, 1976) (Revision received December 4th, 1976) (Accepted January 10th, 1977)
SUMMARY In 1975, in cooperation with 8 C o u n t y Hygienic Stations, total mercury content in fish from rivers and lakes in Hungary was measured. The mercury c o n t e n t in fish muscle-tissue from 164 fish samples averaged 0.36 mg/kg. Average levels in different fish species ranged from 0.10 to 0.57 mg/kg. The a m o u n t of mercury in fish from rivers and lakes, with the exception of the Danube, was, in general, lower than the tolerance level {0.50 mg/kg) as adopted in m a n y countries. Mercury levels in fish from Lak~ Balaton did n o t a m o u n t to more than 0.30 mg/kg. The circulating cold vapour atomic absorption m e t h o d was used to determine the mercury content in the fish samples.
INTRODUCTION As a result of industrial development all over the world, the concentration of mercury in rivers and lakes may have increased, causing a rise of mercury levels in aquatic plants, animals, shell-fish and fish. It has been reported that the average mercury level in fish in 1940 in the U.S.A. ranged from 1.6 to 14 pg/kg, while in 1964 levels were as high as 60 pg/kg. In Japan .in 1964 mercury levels in fish were 10 times higher, 540 pg/kg [1], while in 1970 in Canada, near the coast of the Atlantic Ocean considerable mercury content -20--1000 pg/kg was found in fish [2]. In 1950, in the vicinity of Minamata Bay, Japan, a mass mercury poisoning occurred after consumption of mercury contaminated fish [3]. Even though since that time no severe toxic cases have been reported, the mercury problem still appears to be unsolved. The main sources of the mercury contamination in rivers and lakes are mostly industrial effluents (from electronic-, paper-, colour-industry, etc.}. According to data reported in the U.S.A., mercury contamination of agri-
349
cultural origin amounts to no more than 4.6% of all cases [2]. Since 1949 this Institute has monitored mercury contamination. In the period 1950--1970 residue levels of mercury in bread were investigated in order to control the eventual mixing of untreated cereals with those treated with mercury containing seed dressings. Until 1967 these measurements were performed according to Cieleszky [4], and later by the method described by So6s [5]. Both methods involve sample digestion and the determination of mercury(II) by the dithizone colorimetric procedure. Mercury levels in fish were investigated by the m e t h o d of So6s. The sensitivity, however, of the dithizone colorimetric procedure is not high enough for the assessment of low mercury levels (<0.1 mg/kg), present in fish in Hungary. Therefore, from 1974 the measurements were performed by a cold vapour atomic absorption technique. In 1975, in cooperation with some County Hygienic Stations, mercury levels in fish from rivers and lakes in Hungary were investigated. The County Hygienic Stations of B~cs-Kiskun, B~k6s, Csongr~d, Hajdu-Bihar, Heves, Tolna and Veszp%m counties participated in the collection of the fish samples and their preparation for atomic absorption examination. METHODS AND MATERIALS
Sampling A total of 164 fish specimens were collected from all important rivers and lakes in Hungary. Most samples were obtained from the largest river (Danube) and the largest lake (Balaton), but specimens from artificial ponds (i.e. fish-hatcheries) were also collected. Every species of fish living in Hungary was represented according to frequency of occurrence. Fish fillets of all specimens and liver and kidney from some specimens were examined. Twelve t r o u t samples, serving as controls, were obtained from a mountain river in Hungary, Szalajka, which is not exposed either to industrial or to agricultural mercury contamination, any mercury in this river originating from natural sources.
Analytical procedures Preparation of the samples was carried out according to the procedure recommended by the Perkin-Elmer Co. [6]. One gram of homogenized fish (muscle-tissue, liver or kidney) was transferred to an iodine number flask and 30 ml of concentrated sulfuric acid was slowly added. The stoppered flask was allowed to stand at room temperature for about 15 min, then carefully swirled to help disperse the sample and placed in a water bath of 60°C for 2 h. If, after removal from the water bath, particles were still visible, 5 ml of concentrated sulfuric acid was added and digestion at 60°C was continued for an additional hour. The flask was allowed to cool at room temperature and the solution was slowly poured
350
into another flask containing 50 ml of mercury-free double distilled water (during this procedure the temperature should not rise over 60°C). In small portions 2 g of potassium permanganate crystals was added and the solution was heated at 60°C in a water bath for a few minutes (until KMnO4 dissolved). The permanently purplish red solution was made up with water to 100 ml and kept in a polyethylene flask until analysis (the acid samples may
Absorbanoe
0,300
#~
0,200
0,100
t
J
0,2
I
J
0,4
,
,
0,6
I
I
0,8
i
~
I
J
I
~--
1,0 1,2 pg Hg
Fig. 1. Standard curve f o r a t o m i c a b s o r p t i o n measurement of mercury,
351
be stored in a p o l y e t h y l e n e flask w i t h o u t m ercury loss for 2 weeks). Special a t t e n t i o n should be paid to m e r c u r y levels in all chemicals especially in sulfuric acid. All chemicals used were of analytical reagent quality. Reagent blanks were run with every set of samples, the average value being 0.04 pg m e r c u r y (range 0.02--0.07). Mercury contents were corrected for reagent blanks. To the 100 ml solution, 1--2 drops of 5% KMnO4 solution and 5 ml of 5,6-n-HNO3 were added, and the flask was allowed to stand for 15 sec. After the addition of 5 ml of 18-n-H2SO4 the mixture was allowed to stand for a n o t h e r 45 sec. The excess permanganate was reduced by the addition of 5 ml 1.5% h y d r o x y l a m i n e hydrochloride. If clarification of the solution was n o t achieved, a second 5 ml por t i on of 1.5% h y d r o x y l a m i n e h y d r o c h l o r i d e was added. Then the solution was transferred to the aerator and after the addition o f 5 ml of 10% stannous chloride solution the circulating p u m p was started. Analyses were p e r f o r m e d by a Perkin-Elmcr 403 apparatus, based on the m e t h o d of Hatch and Ott [7], with the following operating conditions: wavelength, 253.7 nm; slit, 4 (0.7 nm); source, mercury hollow cathode lamp. In Fig. 1 the standard curve used in our measurements is presented. It was reproducible at any time. To 1 g o f hom oge ni z e d carp samples amounts of 0.05, 0.1, 0.5 and 1.0 pg m e r c u r y were added in the form of HgC12. Generally 2--4 parallel measurements were made. Average recovery _+ S.D. with 11 samples was 95 -+ 6.7%. In consideration of this almost 100% recovery correction was regarded as unnecessary. To establish w he t he r a l-g specimen taken from a fish fillet can be regarded a representative for the whole sample, 1-g amounts of fish-muscle tissue were removed from 4 different parts of a carp and homogenized. From the toxico-hygienic viewpoint the differences among the results were n o t notable (the m er c ur y c o n t e n t ranged f r om 0.11 to 0.15 mg/kg). RESULTS AND DISCUSSION Mercury c o n t e n t in different fish species from Hungary is presented in Table I. It may be seen that m e r cur y levels, in the species examined, generally do n o t exceed or only slightly exceed the level permitted in most countries, namely 0.5 mg/kg. Especially in carp, most frequently used in Hungary for h u man consumption, m e r cur y c o n t e n t is relatively low. In bass and crucian the mer cu r y c o n t e n t seems to be higher than in ot her fishes because of one exceptionally high value (in brackets) f o und in each species. By omitting the latter the average value in the case of bass does not a m o u n t to more than 0.12 mg/kg and in the case of crucian to more than 0.43 mg/kg. These results are very close to values obtained from ot her fish species. Mercury levels in muscle-tissue, liver and kidney of 3 species most f r eq u en tly consumed in Hungary are presented in Table II.
352
TABLE I M ER C UR Y CONTENT IN MUSCLE-TISSUE OF FISH SPECIES IN H U N G A R Y Fish species
Carp Cyprinus carpio Bream Abramis brama Pike-perch Lucioperca sandra Silure Amiurus nebulosus Hypophthalamyctis molitrix et nobilis Pike Esox lucius Tench 7~nca vulgaris Bass Perca fluviatilis Aspius rapax Crucian Eupomotis aureus Other fishes Trout (controls) Salmo fario
S'E" = - V
Number of samples (n)
Mercury content + S.E. (mg/kg)
63
0.24 +- 0.06
28
0.42 -+ 0.11
13
0.57 + 0.10
11 11
0.56 + 0.19 0.10 -+ 0.03
6
0.25 -+ 0.03
6
0.47 -+ 0.06
5 4
1.16 + 0.75 [3.8] 0.10 -+ 0.05
4 14
0.82 -+ 0.41 [2.0] 0.30 -+ 0.12
12
0.14 + 0.02
n ( n - - 1)
In t h e l i v e r o f t h e 3 f i s h s p e c i e s l o w e r m e r c u r y l e v e l s w e r e f o u n d t h a n in t h e m u s c l e - t i s s u e . A c c o r d i n g t o d a t a in l i t e r a t u r e in g e n e r a l m e r c u r y s e e m s t o b e m o r e e n r i c h e d in l i v e r t h a n in m u s c l e - t i s s u e [ 8 , 9 ] . H o w e v e r , t h i s t r e n d a p p e a r s t o b e t y p i c a l o n l y f o r fish o r i g i n a t i n g f r o m w a t e r s h i g h l y c o n t a m i nated with mercury. I n T a b l e I I I m e r c u r y l e v e l s o f fish s a m p l e s o b t a i n e d f r o m d i f f e r e n t sites are s u m m a r i z e d . TABLE II MER C UR Y CONTENT IN MUSCLE-TISSUE AND ORGANS OF FISHES FROM" HUNGARY Fish species
Carp Bream Pikeperch
Musle-tissue
Liver
Hg (mg/kg) + S.E.
n
0.24 -+ 0.06 0.42 +- 0.11 0.57 -+ 0.10
Kidney
Hg (mg/kg) -+ S.E.
n
63 28
0.13 + 0.04 0.16 -+ 0.19
20 11
13
0.23 + 0.00
5
a
a
Hg (mg/kg) -+ S.E.
n a
0.34 + 0.33 0.03
6 1
--
--
a n = number of samples.
353
TABLE III MERCURY CONTENT IN MUSCLE-TISSUE OF FISH FROM DIFFERENT SITES OF SAMPLING Site of sampling
Number of samples
Mercury content (mg/kg) Average
Range
Lake Balaton
27
0.30
0.00--1.80
Other lakes and artificial ponds
74
0.25
0.00--3.40
River Danube
27
0.59
0.00--1.30
Tisza and other rivers
36
0.42
0.00--3.80
Szalajka a
12
0.14
0.05--0.25
Average of all samples (1975) 164 0.36 0.00--3.80 a Especially clean (uncontaminated) mountain river, ~ontrol territory. F r o m t h e s e d a t a it can be seen t h a t in H u n g a r y m e r c u r y c o n t e n t in fish f r o m rivers is in general higher t h a n t h a t in fish f r o m lakes and artificial p o n d s , t h o u g h in s o m e cases the l a t t e r m a y also c o n t a i n - h i g h a m o u n t s . T h e f a c t t h a t m e r c u r y levels in fish f r o m L a k e B a l a t o n are a p p r o x i m a t e l y identical to t h e levels o b s e r v e d in fish originating, a c c o r d i n g to literature, f r o m m e r c u r y u n c o n t a m i n a t e d rivers and lakes, is v e r y f a v o u r a b l e f r o m t h e hygienic p o i n t o f view [ 1 0 ] . T h e average m e r c u r y c o n t e n t in fish f r o m all rivers and lakes in H u n g a r y , with t h e e x c e p t i o n o f the D a n u b e , is l o w e r t h a n t h e t o l e r a n c e level established in several c o u n t r i e s (0.5 m g / k g ) . It s h o u l d also be n o t e d t h a t in 1 9 7 2 H u n g a r y r e c o m m e n d e d to t h e WHO, c o n s i d e r i n g fish c o n s u m p t i o n figures in t h a t c o u n t r y , t h a t 0.5 m g / k g o f m e r c u r y s h o u l d be r e g a r d e d as p e r m i s s i b l e in i m p o r t e d sea fish p r o d u c t s . ACKNOWLEDGEMENTS T h a n k s are due t o t h e C o u n t y H y g i e n i c S t a t i o n s f o r t h e h e l p in s a m p l e p r e p a r a t i o n s , as well as to M a g d o l n a L~n~rd and J u d i t Kosty~il f o r t e c h n i c a l assistance. REFERENCES 1 A.G. Hugunin, J. Milk Food Technol., 38 (1975) 354. 2 F.M. D'Itri, The Environmental Mercury Problem, CRC Press, Cleveland, Ohio, 1972. 3 L. Kurland, S.N. Faro and H. Seidler, World Neurol., 1 (1960) 370.
354
4 5 6 7 8 9
V. Cieleszky, Kiserletugyi Kozl., 47--49 (1947) 70. K. So6s, Elelmiszervizsgalati Kozl., 13 (1967) 215. Perkin-Elmer Mercury Analysis System, Instructions, Norwalk, Connecticut, 1972. W.R. Hatch and W.L. Ott, Anal. Chem., 40 (1968) 2085. A.A. Reimer and R. Reimer, Bull. Environ. Contam. Toxicol., 14 (1975) 105. J.B. Rivers, J.E. Pearson and C.D. Schultz, Bull. Environ. Contain. Toxicol., 8 (1972) 257. 10 J.G. Saha, Residue Rev., 42 (1972) 103.
355
DETERMINATION OF MERCURY IN FISH FROM RIVERS AND LAKES IN HUNGARY BY ATOMIC ABSORPTION TECHNIQUE
ANNA GERGELY, KATALIN SO(~S, L/kSZL6 ERDELYI and VILMOS CIELESZKY Institute of Nutrition, 1097 Budapest Gy6li ut 3/a (Hungary)
(Received September 14th, 1976) (Revision received December 4th, 1976) (Accepted January 10th, 1977)
SUMMARY In 1975, in cooperation with 8 C o u n t y Hygienic Stations, total mercury content in fish from rivers and lakes in Hungary was measured. The mercury c o n t e n t in fish muscle-tissue from 164 fish samples averaged 0.36 mg/kg. Average levels in different fish species ranged from 0.10 to 0.57 mg/kg. The a m o u n t of mercury in fish from rivers and lakes, with the exception of the Danube, was, in general, lower than the tolerance level {0.50 mg/kg) as adopted in m a n y countries. Mercury levels in fish from Lak~ Balaton did n o t a m o u n t to more than 0.30 mg/kg. The circulating cold vapour atomic absorption m e t h o d was used to determine the mercury content in the fish samples.
INTRODUCTION As a result of industrial development all over the world, the concentration of mercury in rivers and lakes may have increased, causing a rise of mercury levels in aquatic plants, animals, shell-fish and fish. It has been reported that the average mercury level in fish in 1940 in the U.S.A. ranged from 1.6 to 14 pg/kg, while in 1964 levels were as high as 60 pg/kg. In Japan .in 1964 mercury levels in fish were 10 times higher, 540 pg/kg [1], while in 1970 in Canada, near the coast of the Atlantic Ocean considerable mercury content -20--1000 pg/kg was found in fish [2]. In 1950, in the vicinity of Minamata Bay, Japan, a mass mercury poisoning occurred after consumption of mercury contaminated fish [3]. Even though since that time no severe toxic cases have been reported, the mercury problem still appears to be unsolved. The main sources of the mercury contamination in rivers and lakes are mostly industrial effluents (from electronic-, paper-, colour-industry, etc.}. According to data reported in the U.S.A., mercury contamination of agri-
349
cultural origin amounts to no more than 4.6% of all cases [2]. Since 1949 this Institute has monitored mercury contamination. In the period 1950--1970 residue levels of mercury in bread were investigated in order to control the eventual mixing of untreated cereals with those treated with mercury containing seed dressings. Until 1967 these measurements were performed according to Cieleszky [4], and later by the method described by So6s [5]. Both methods involve sample digestion and the determination of mercury(II) by the dithizone colorimetric procedure. Mercury levels in fish were investigated by the m e t h o d of So6s. The sensitivity, however, of the dithizone colorimetric procedure is not high enough for the assessment of low mercury levels (<0.1 mg/kg), present in fish in Hungary. Therefore, from 1974 the measurements were performed by a cold vapour atomic absorption technique. In 1975, in cooperation with some County Hygienic Stations, mercury levels in fish from rivers and lakes in Hungary were investigated. The County Hygienic Stations of B~cs-Kiskun, B~k6s, Csongr~d, Hajdu-Bihar, Heves, Tolna and Veszp%m counties participated in the collection of the fish samples and their preparation for atomic absorption examination. METHODS AND MATERIALS
Sampling A total of 164 fish specimens were collected from all important rivers and lakes in Hungary. Most samples were obtained from the largest river (Danube) and the largest lake (Balaton), but specimens from artificial ponds (i.e. fish-hatcheries) were also collected. Every species of fish living in Hungary was represented according to frequency of occurrence. Fish fillets of all specimens and liver and kidney from some specimens were examined. Twelve t r o u t samples, serving as controls, were obtained from a mountain river in Hungary, Szalajka, which is not exposed either to industrial or to agricultural mercury contamination, any mercury in this river originating from natural sources.
Analytical procedures Preparation of the samples was carried out according to the procedure recommended by the Perkin-Elmer Co. [6]. One gram of homogenized fish (muscle-tissue, liver or kidney) was transferred to an iodine number flask and 30 ml of concentrated sulfuric acid was slowly added. The stoppered flask was allowed to stand at room temperature for about 15 min, then carefully swirled to help disperse the sample and placed in a water bath of 60°C for 2 h. If, after removal from the water bath, particles were still visible, 5 ml of concentrated sulfuric acid was added and digestion at 60°C was continued for an additional hour. The flask was allowed to cool at room temperature and the solution was slowly poured
350
into another flask containing 50 ml of mercury-free double distilled water (during this procedure the temperature should not rise over 60°C). In small portions 2 g of potassium permanganate crystals was added and the solution was heated at 60°C in a water bath for a few minutes (until KMnO4 dissolved). The permanently purplish red solution was made up with water to 100 ml and kept in a polyethylene flask until analysis (the acid samples may
Absorbanoe
0,300
#~
0,200
0,100
t
J
0,2
I
J
0,4
,
,
0,6
I
I
0,8
i
~
I
J
I
~--
1,0 1,2 pg Hg
Fig. 1. Standard curve f o r a t o m i c a b s o r p t i o n measurement of mercury,
351
be stored in a p o l y e t h y l e n e flask w i t h o u t m ercury loss for 2 weeks). Special a t t e n t i o n should be paid to m e r c u r y levels in all chemicals especially in sulfuric acid. All chemicals used were of analytical reagent quality. Reagent blanks were run with every set of samples, the average value being 0.04 pg m e r c u r y (range 0.02--0.07). Mercury contents were corrected for reagent blanks. To the 100 ml solution, 1--2 drops of 5% KMnO4 solution and 5 ml of 5,6-n-HNO3 were added, and the flask was allowed to stand for 15 sec. After the addition of 5 ml of 18-n-H2SO4 the mixture was allowed to stand for a n o t h e r 45 sec. The excess permanganate was reduced by the addition of 5 ml 1.5% h y d r o x y l a m i n e hydrochloride. If clarification of the solution was n o t achieved, a second 5 ml por t i on of 1.5% h y d r o x y l a m i n e h y d r o c h l o r i d e was added. Then the solution was transferred to the aerator and after the addition o f 5 ml of 10% stannous chloride solution the circulating p u m p was started. Analyses were p e r f o r m e d by a Perkin-Elmcr 403 apparatus, based on the m e t h o d of Hatch and Ott [7], with the following operating conditions: wavelength, 253.7 nm; slit, 4 (0.7 nm); source, mercury hollow cathode lamp. In Fig. 1 the standard curve used in our measurements is presented. It was reproducible at any time. To 1 g o f hom oge ni z e d carp samples amounts of 0.05, 0.1, 0.5 and 1.0 pg m e r c u r y were added in the form of HgC12. Generally 2--4 parallel measurements were made. Average recovery _+ S.D. with 11 samples was 95 -+ 6.7%. In consideration of this almost 100% recovery correction was regarded as unnecessary. To establish w he t he r a l-g specimen taken from a fish fillet can be regarded a representative for the whole sample, 1-g amounts of fish-muscle tissue were removed from 4 different parts of a carp and homogenized. From the toxico-hygienic viewpoint the differences among the results were n o t notable (the m er c ur y c o n t e n t ranged f r om 0.11 to 0.15 mg/kg). RESULTS AND DISCUSSION Mercury c o n t e n t in different fish species from Hungary is presented in Table I. It may be seen that m e r cur y levels, in the species examined, generally do n o t exceed or only slightly exceed the level permitted in most countries, namely 0.5 mg/kg. Especially in carp, most frequently used in Hungary for h u man consumption, m e r cur y c o n t e n t is relatively low. In bass and crucian the mer cu r y c o n t e n t seems to be higher than in ot her fishes because of one exceptionally high value (in brackets) f o und in each species. By omitting the latter the average value in the case of bass does not a m o u n t to more than 0.12 mg/kg and in the case of crucian to more than 0.43 mg/kg. These results are very close to values obtained from ot her fish species. Mercury levels in muscle-tissue, liver and kidney of 3 species most f r eq u en tly consumed in Hungary are presented in Table II.
352
TABLE I M ER C UR Y CONTENT IN MUSCLE-TISSUE OF FISH SPECIES IN H U N G A R Y Fish species
Carp Cyprinus carpio Bream Abramis brama Pike-perch Lucioperca sandra Silure Amiurus nebulosus Hypophthalamyctis molitrix et nobilis Pike Esox lucius Tench 7~nca vulgaris Bass Perca fluviatilis Aspius rapax Crucian Eupomotis aureus Other fishes Trout (controls) Salmo fario
S'E" = - V
Number of samples (n)
Mercury content + S.E. (mg/kg)
63
0.24 +- 0.06
28
0.42 -+ 0.11
13
0.57 + 0.10
11 11
0.56 + 0.19 0.10 -+ 0.03
6
0.25 -+ 0.03
6
0.47 -+ 0.06
5 4
1.16 + 0.75 [3.8] 0.10 -+ 0.05
4 14
0.82 -+ 0.41 [2.0] 0.30 -+ 0.12
12
0.14 + 0.02
n ( n - - 1)
In t h e l i v e r o f t h e 3 f i s h s p e c i e s l o w e r m e r c u r y l e v e l s w e r e f o u n d t h a n in t h e m u s c l e - t i s s u e . A c c o r d i n g t o d a t a in l i t e r a t u r e in g e n e r a l m e r c u r y s e e m s t o b e m o r e e n r i c h e d in l i v e r t h a n in m u s c l e - t i s s u e [ 8 , 9 ] . H o w e v e r , t h i s t r e n d a p p e a r s t o b e t y p i c a l o n l y f o r fish o r i g i n a t i n g f r o m w a t e r s h i g h l y c o n t a m i nated with mercury. I n T a b l e I I I m e r c u r y l e v e l s o f fish s a m p l e s o b t a i n e d f r o m d i f f e r e n t sites are s u m m a r i z e d . TABLE II MER C UR Y CONTENT IN MUSCLE-TISSUE AND ORGANS OF FISHES FROM" HUNGARY Fish species
Carp Bream Pikeperch
Musle-tissue
Liver
Hg (mg/kg) + S.E.
n
0.24 -+ 0.06 0.42 +- 0.11 0.57 -+ 0.10
Kidney
Hg (mg/kg) -+ S.E.
n
63 28
0.13 + 0.04 0.16 -+ 0.19
20 11
13
0.23 + 0.00
5
a
a
Hg (mg/kg) -+ S.E.
n a
0.34 + 0.33 0.03
6 1
--
--
a n = number of samples.
353
TABLE III MERCURY CONTENT IN MUSCLE-TISSUE OF FISH FROM DIFFERENT SITES OF SAMPLING Site of sampling
Number of samples
Mercury content (mg/kg) Average
Range
Lake Balaton
27
0.30
0.00--1.80
Other lakes and artificial ponds
74
0.25
0.00--3.40
River Danube
27
0.59
0.00--1.30
Tisza and other rivers
36
0.42
0.00--3.80
Szalajka a
12
0.14
0.05--0.25
Average of all samples (1975) 164 0.36 0.00--3.80 a Especially clean (uncontaminated) mountain river, ~ontrol territory. F r o m t h e s e d a t a it can be seen t h a t in H u n g a r y m e r c u r y c o n t e n t in fish f r o m rivers is in general higher t h a n t h a t in fish f r o m lakes and artificial p o n d s , t h o u g h in s o m e cases the l a t t e r m a y also c o n t a i n - h i g h a m o u n t s . T h e f a c t t h a t m e r c u r y levels in fish f r o m L a k e B a l a t o n are a p p r o x i m a t e l y identical to t h e levels o b s e r v e d in fish originating, a c c o r d i n g to literature, f r o m m e r c u r y u n c o n t a m i n a t e d rivers and lakes, is v e r y f a v o u r a b l e f r o m t h e hygienic p o i n t o f view [ 1 0 ] . T h e average m e r c u r y c o n t e n t in fish f r o m all rivers and lakes in H u n g a r y , with t h e e x c e p t i o n o f the D a n u b e , is l o w e r t h a n t h e t o l e r a n c e level established in several c o u n t r i e s (0.5 m g / k g ) . It s h o u l d also be n o t e d t h a t in 1 9 7 2 H u n g a r y r e c o m m e n d e d to t h e WHO, c o n s i d e r i n g fish c o n s u m p t i o n figures in t h a t c o u n t r y , t h a t 0.5 m g / k g o f m e r c u r y s h o u l d be r e g a r d e d as p e r m i s s i b l e in i m p o r t e d sea fish p r o d u c t s . ACKNOWLEDGEMENTS T h a n k s are due t o t h e C o u n t y H y g i e n i c S t a t i o n s f o r t h e h e l p in s a m p l e p r e p a r a t i o n s , as well as to M a g d o l n a L~n~rd and J u d i t Kosty~il f o r t e c h n i c a l assistance. REFERENCES 1 A.G. Hugunin, J. Milk Food Technol., 38 (1975) 354. 2 F.M. D'Itri, The Environmental Mercury Problem, CRC Press, Cleveland, Ohio, 1972. 3 L. Kurland, S.N. Faro and H. Seidler, World Neurol., 1 (1960) 370.
354
4 5 6 7 8 9
V. Cieleszky, Kiserletugyi Kozl., 47--49 (1947) 70. K. So6s, Elelmiszervizsgalati Kozl., 13 (1967) 215. Perkin-Elmer Mercury Analysis System, Instructions, Norwalk, Connecticut, 1972. W.R. Hatch and W.L. Ott, Anal. Chem., 40 (1968) 2085. A.A. Reimer and R. Reimer, Bull. Environ. Contam. Toxicol., 14 (1975) 105. J.B. Rivers, J.E. Pearson and C.D. Schultz, Bull. Environ. Contain. Toxicol., 8 (1972) 257. 10 J.G. Saha, Residue Rev., 42 (1972) 103.
355