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Passage of metals to freshwater fish from their food
Water Research Vol. 12, pp. 395 to 398. O Pergamon Press Ltd.. 1978. Printed in Greal Britain.
0043-1354/78/0601.0395502.00/0
PASSAGE OF METALS TO FRESHWATER FISH FROM THEIR FOOD F. M. PATRICK* and M. W. Lotrrrr Microbiology Department, Otago University, Dunedin, New Zealand
(Received 22 December 1977) Abstract--Following work showing that Cr, Cu, Mn, Fe, Pb and Zn could be concentrated by tubificid worms aRer ingesting metal-enriched heterotrophic bacteria, experiments were carried out in which fish, fed these worms, showed increased metal levels in their tissues after four days. Only Pb was found in increased concentrations afler a shorter period of two days. Both young and older fish were used in the experiments, and the results indicate that increased levels of most metals in the fish reflect the concentrations of the metals in their food if the fish are exposed to the food for longer than two to four days, and that the age of the fish has an effect on their final metal concentrations.
INTRODUCTION
Previous work indicated that small amounts of metals in effluents could be concentrated by bacteria and passed to tubificids consuming them (Patrick & Loutit, 1976). If metals are passed to fish consuming such tubificids, an explanation may be possible of the high levels of certain metals found in eels collected from below effluent entry points in a river under study (Loutit, Patrick & Malthus, 1973). Studies elsewhere have shown that metal levels in fish increased as metal levels in water, sediment and invertebrates increased (Pillay et al., 1972; Mathis & Cummings, 1973; Walter, June & Brown, 1973; Ratkowsky, Dix & Wilson, 1975) but no experiments showing direct connection between elevated metal levels in tubiflcids and fish have been recorded. The only comparable experiment is that in which tubificids containing the insecticide H E O D were fed to fish, which subsequently showed increased H E O D levels (Chadwick & Brocksen, 1969). As tubificids are ingested by many species of fish and eels, (Hynes, 1960; Marples, 1962) it seemed logical to postulate that metals may be transferred to fish through the worms, thus completing a foodchain starting with heterotrophic, sediment-inhabiting bacteria. This paper describes experiments designed to investigate this postulate. MATERIALS AND METHODS
Tubificids containin0 metals Juvenile tubificid worms (lower 50% of the population size range) were fed bacteria grown with or without heavy metals as previously described (Patrick & Loutit, 1976). In these experiments, however, the concentration of each of the six metals was 1 mg 1- ~ of medium.
the experimental fish. Twenty four 21 Pyrex dishes each containing 1 1 aged tapwater and 200g Ballotini spheres (2-4 mm diameter) were placed at 25°C in constant light with a non-reflective cloth between each dish. The dishes were divided into two sets of 12 and each set into six pairs. Into each dish of one set were placed three juvenile fish (60-80 mg dry weight each) and into each dish of the second set were placed three older fish (140-160rag dry wt each). The day of commencement of the experiment was designated day 0, and all fish were fed commercial fish food ("Nippy Nip, fine grade", 9-10 mg wet wt per fish) on this day. The fish in one of each pair of dishes were then fed the same amount of fish food on days 2, 4, 6, 8, 10, 12 and 14, and tubificids (6 per fish, I0 mg approximately wet wt per fish) fed bacteria grown in the absence of heavy metals every alternate day until day 13. Similarly the fish in the second dish of each pair were fed alternatively, fish food and worms fed bacteria grown in the presence of 1 mg 1-~ of each metal. One pair of dishes in each set was used as a control, and the fish in these dishes fed commercial fish food each day, the fish in one dish being harvested on day 0 and the fish in the other being harvested on day 14. One pair of the remaining dishes from each set was removed from incubation on days, 2, 4, 7, 11 and 14, and each fish in every dish analysed for metal levels (using dry ashing followed by atomic absorption spectrophotometry of the acid extracts of the ash), after having their stomach and alimentary tract removed. Results from three replicate fish from each dish were analysed statistically (Fisher's F Test). Samples of water from each dish were also analysed for metal levels on the day of harvesting. Fish faeces were unable to be analysed due to the small amounts produced and the difficulty in collecting the faecal material. Replicate samples of the commercial fish food and the tubificid worms (both those fed bacteria with and without elevated metal levels), were analysed for metal levels before, during and after the 14 day incubation period.
Fish feeding experiments Tropical fish (Hyphessobrycon serpae) were selected as *Present address: Fisheries Research Division, P.O. Box 19062, Wellington, New Zealand. 395
RESULTS AND DISCUSSION
Eels would have been the ideal experimental animal, but availability and size precluded their use, and so tropical fish known to consume tuhificids were used instead. In initial experiments fish were fed worms with and without elevated metal levels for 2 and 4 days. There
396
F . M . PATRICK and M. W. LOUTIT Table 1. Estimates of metal levels (mR kg- 1 dry weight) in tubificids and commercial fish food fed to fish and in fish fed commercial fish food for 14 days. Levels of metal in the tank water are given as mR l - l Cr Tubificids fed bacteria grown without added metals Tubificids fed bacteria grown with added metals Young fish Day 0 Day 14 Old fish Day 0 Day 14 Commercial fish food Tank water Range of estimations
Cu
Mn
Fe
Pb
Zn
14.58"
144.44
8.47
556.11
111.15
336.5
32.25
231.08
13.67
869.25
160.41
663.7
2.40 4.81
92.40 106.46
8.68 16.14
171.32 120.19
3.59 15.45
239.9 243.5
3.15 2.82 3.12"1" ND
58.23 11.38 111.33 9.30 7.94 65.75 0.10 ND-0.02 -0.25
94.19 8.23 149.6 101.47 17.47 298.8 272.67 12.79 404.8 0.06 ND-O.06 ND-0.04 -0.18
* Average of estimates on three replicate pooled samples. t Mean of estimates on five separate samples. ND = not detected at a level of 0.02 mg1-1. were few differences in metal levels in the fish except for C r and Pb. As levels of these metals appeared higher at the end of these experiments it was decided to extend the feeding period for 14 days. The levels of metals in the worms and commercial fish food are s h o w n in Table 1, as are the levels of metals in b o t h young and old fish on day 0 and on day 14 after being fed commercial fish food only. Although the levels of metals in the commercial food were lower than in worms fed bacteria grown in the
absence of metals (except for Zn), the quantity of food ingested and the possibly greater availability of the metals in the fish food compared with the worms were sufficient to cause elevated metal levels in the fish flesh after 14 days; often to a greater degree than in fish fed alternatively commercial fish food and such worms (Table 2). F r o m the patterns of uptake of each metal by young and old fish shown in Figs. 1 and 2, there is no d o u b t that metal levels in fish fed worms con-
Table 2. Statistical analysis of estimates of metal levels in mg kg- 1 dry wt in day 14 fish fed tubificid worms containing various levels of metals Cr Young fish fed worms fed bacteria grown without metals Young fish fed worms fed on bacteria grown with metals Young fish fed Nippy Nip only Old fish fed worms fed bacteria grown without metals Old fish fed worms fed bacteria grown with metals Old fish fed Nippy Nip only % Recovery (Gorsuch, 1970)
Cu
Mn
Fe
Pb
Zn
3.02A
79.78A
8.83A
112.32A
17.67A
229.8A
5.91B
199.42B
19.99B
181.31B
36.28B
499.2B
4.81C
106.46C
16.14C
120.19A
14.38A
243.5C
2.58 D
57.20D
7.95A
92A2C
7.60C
135.3 D
9.06E
146.08E
18.50BC
144.08D
36.29B
308.2E
2.82AD
111.33C
9.30A
101.47C
17.47A
298.8E
91.4
99.8
83.8
99.4
95.8
98.3
For any individual metal, means of one letter are significantly (1%) different from means of any other letter, ~'i=.: A is different from B, C, D, E etc., but not different from A, AB, AC etc.
Passage of metals to freshwater fish copper
:hroadum
mal~nese
_
Y
"..
s
~
30
I,
ZOO
ZO
2" e " ~ - r
,oo~,~_~
•~
-
1
I
0
iron
,o, 1
o! leod
O
40 A
400
"~ 3O0
30 ~
30O
~¢200
20
200'
10
100
O
O
~' 100 I
i
i
i
~
J
~ ~
°t,t,tq,t,ot t,, fed
397
doys--~
worms off doys orrowed
Fig. 1. Estimates of metal levels in mg kg- s dry wt in young fish fed tubificid worms containing various levels of metals. • = Fish fed tubificids fed on bacteria grown without metals. • = Fish fed tubificids fed on bacteria grown with I mg 1-' of each metal. Results expressed as a mean of estimates made on each of three fish from each dish.
taining elevated levels of metals were higher than those fed either commercial food only, or the worms containing lower levels of metals. The increase in Cr and Pb in both old and young fish were particularly marked. Uptake of Zn, Pb, and to a lesser extent Fe and Cu, was greater in young than in old fish. This could be due to the older larger fish consuming less metal when expressed as a concentration because they were fed the same weight of food as the young fish. It has been shown, however, that older members of two marine species of fish contained lower levels of Cu, Fe and Zn than younger members of the same species (Cross et al., 1973), and may be due in part to different adsorption rates across the gut, or more efficient excretion in older fish.
chromium
Statistical analysis of the differences in metal levels between all fish harvested on day 14 are shown in Table 2. These differences may have been augmented by absorption of metals from the water, but absorption should have been comparable in all tanks. The water metal levels shown in Table I were daily differences occurring in all tanks irrespective of feeding regime, fish age and time. Another combination of factors which could possibly account for differences in metal levels in the fish is the inability to match the fish exactly for size, weight or metal content on day 0, and the worms analysed for metal levels were not those actually fed to the fish. Hence differences in metal levels in the fish from one tank to another, and possible differences in metal levels in the food
copper
mongonese
30 5 4
20
20O
3¸ 2
10'
1
zinc
ieod
i 20 f
11~,
~
300 200 100
I I I [
I
I I
otzt4 t6 tellotlzll,
0 days--z-(arrow.ledworms)
Fig. 2. Estimates of metal levels in mg kg- ' dry wt in old fish fed tubificid worms containing various levels of metals. • = Fish fed tubificids fed on bacteria grown without metals. • = Fish fed tubificids fed on bacteria grown with 1 mgl-Z of each metal. Results expressed as a mean of estimates made on each of three fish from each dish. WR. 12r6
C
398
F.M. P^rRtCK and M. W. Lou-rrr
fed to the fish may account for a portion of any measured metal level differences in the fish during the experiments. The fact that there were consistent, heightened metal levels in fish fed the worms containing elevated levels of metals compared with all other fish irrespective of diet, indicates that a metal-contaminated diet is a significant source of increased metal levels in fish. The increases appeared after the second day, and this may support the observation that a single dose of metals is almost eliminated or excreted in a short time, but a small residual remains in the body, becoming measurable as a significant increase only after prolonged exposure to the metal-contaminated food (Bryan, 1971). The implications of these results are interesting when considered with other findings. Several genera of bacteria from river sediments are able to accumulate small concentrations of metals present in the water to a marked degree (Patrick & Loutit, 1976). Bacterial numbers and heavy metal levels in the river under study are higher in sediments below effluent entry points than above. Certain nutrients in the effluents apparently stimulate bacterial growth rates, leading to these higher numbers in the polluted sediments (Hynes, 1960; Curtis & Harrington, 1970; Brasfield, 1972; Cole, 1973). It is likely that the small concentrations of metals in the effluents are adsorbed or absorbed by the large number of bacteria in the sediments, and hence removed from the water and prevented from dispersing. Tubificid worms, which browse through sediments for food (Brinkhurst & Chua, 1969; Brinkhurst, Chua & Kaushik, 1972) ingest these bacteria, and so take in the bound metals. These metal-enriched worms are then consumed by fish, and thus the metals are able to be passed along the food chain. Where the diet is largely of these metal-enriched tubificids, the fish will, after a prolonged period of feeding, have heightened metal levels in their tissues. Some increase may also be due to absorption from the surrounding water. The relative importance of the means of metal uptake is likely to vary according to the concentrations and forms of metals in the food, in the organisms and the water surrounding the fish. In certain rivers where effluents reduce the number of food species very markedly (Cairns, Lanza & Parker, 1972; Cairns, 1974) the surviving fish must ingest large numbers of a smaller variety of food species, which may have become heavily contaminated with pollutant metals. Acknowledoement.~---This work was supported by a grant from the Scientific Research Distribution Committee.
REFERENCES
Brasfield H. (t972) Environmental factors correlated with size of bacterial populations in a polluted stream. Appl. Microbiol. 24, 349-352. Brinkhurst R. O. & Chua K. E. (1969) A preliminary investigation of the exploitation of some potential nutritional resources by three sympatic tubificid oligochaetcs. J. Fish. Res. Bd Can. 26, 2659-2668. Brinkhurst R. O., Chua K. E. & Kaushik N. 11972) Interspecific interactions and selective feeding by tubificid oligochaetes. Limnol. Oceano.q. 17, 122 133. Bryan G. W. (1971) The effect of heavy metals Iother than mercury) on marine and estuarine organisms. Proc. R. Soc. (Lond.) B177, 389-410. Cairns J. (1974) Indicator species vs the concept of a community structure as an index of pollution. War. Re.s. Bull. 10, 338-347. Cairns J. J., Lanza G. R. S. & Parker B. C. (1972~ Pollution-related structural and functional changes in aquatic communities with emphasis on freshwater algae and protozoa. Proc. Acad. nat. Sci. Philad. 124, 79-127. Chadwick G. G. & Brocksen R. W. t1969) Accumulatton of dieldrin by fish and selected fish-food organisms, d. Wildlife Mana9. 33, 693-700. Cole R. A. (1973l Stream community response to nutrient enrichment, d. War. Pollut. Control Fed. 45, 1874 1888. Cross F. A., Hardy L. H.. Jones N. Y. &Barger R. T. (1973) Relation between total body weight and concentrations of manganese, iron, copper, zinc and mercury in white muscle of bluefish (Pomatomus saltatrix) and a batbyl-demersal fish Antimora rostrata. J. Fish. Res. Bd Can. 30, 1287-1291. Curtis E. J. C. & Harrington D. W. [1970) Effects of organic wastes on rivers. Proc. Btochem. April, 44-62. Gorsuch T. T. (1970) The Destruction of Or qanic Matter. 1st Edn. Pergamon Press, Oxford. Hynes H. B. N. (1960) The Biology of Polluted Waters. 1st Edn 202 pp. Liverpool University Press. Liverpool. Loutit M. W., Partick F. M. & Malthus R. S. [19731 The role of metal-concentrating bacteria in a food chain in a river receiving effluent. Proc. Unit'. Otago Med. School 51, 37--38. Marples B. J. (1962) An Introduction to Freshwater Lift, in New Zealand. 1st Edn. Whitcombe & Tombs. ChrLstchurch, New Zealand. Mathis B. J. & Cummings T. F. 11973~ Sclcctcd metals in river sediment, water and ammals. J. 14"at. Polhtt. Control Fed. 45, 1573 1583. Patrick F. M. & Loutit M. W. 11976) Passagc of mctal~ in effluents, through bacteria to higher organisms. Water Res. 10, 333-335. Pillay K. K. S., Thomas C. C., Sondel J. A. & Hychc C. M. (1972) Mercury pollution of Lake Eric ccosphere. Envir. Res. 5, 172--181~ Ratkowsky D. A., Dix T. G. & Wilson K. C. (1975) Mcrcury in fish in the Derwent Estuary, Tasmania. and ~ts relation to position of the fish in the food chain..4ust. J. mar. Freshwat. Res. 26, 223-231. Walter C. M., June F. C. & Brown H. G. ~1973) Mercury in fish, sediments and water in Lake Oake, South Dakota. J. Wut. Pollut. Control Fed. 45, 2203 2210.
0043-1354/78/0601.0395502.00/0
PASSAGE OF METALS TO FRESHWATER FISH FROM THEIR FOOD F. M. PATRICK* and M. W. Lotrrrr Microbiology Department, Otago University, Dunedin, New Zealand
(Received 22 December 1977) Abstract--Following work showing that Cr, Cu, Mn, Fe, Pb and Zn could be concentrated by tubificid worms aRer ingesting metal-enriched heterotrophic bacteria, experiments were carried out in which fish, fed these worms, showed increased metal levels in their tissues after four days. Only Pb was found in increased concentrations afler a shorter period of two days. Both young and older fish were used in the experiments, and the results indicate that increased levels of most metals in the fish reflect the concentrations of the metals in their food if the fish are exposed to the food for longer than two to four days, and that the age of the fish has an effect on their final metal concentrations.
INTRODUCTION
Previous work indicated that small amounts of metals in effluents could be concentrated by bacteria and passed to tubificids consuming them (Patrick & Loutit, 1976). If metals are passed to fish consuming such tubificids, an explanation may be possible of the high levels of certain metals found in eels collected from below effluent entry points in a river under study (Loutit, Patrick & Malthus, 1973). Studies elsewhere have shown that metal levels in fish increased as metal levels in water, sediment and invertebrates increased (Pillay et al., 1972; Mathis & Cummings, 1973; Walter, June & Brown, 1973; Ratkowsky, Dix & Wilson, 1975) but no experiments showing direct connection between elevated metal levels in tubiflcids and fish have been recorded. The only comparable experiment is that in which tubificids containing the insecticide H E O D were fed to fish, which subsequently showed increased H E O D levels (Chadwick & Brocksen, 1969). As tubificids are ingested by many species of fish and eels, (Hynes, 1960; Marples, 1962) it seemed logical to postulate that metals may be transferred to fish through the worms, thus completing a foodchain starting with heterotrophic, sediment-inhabiting bacteria. This paper describes experiments designed to investigate this postulate. MATERIALS AND METHODS
Tubificids containin0 metals Juvenile tubificid worms (lower 50% of the population size range) were fed bacteria grown with or without heavy metals as previously described (Patrick & Loutit, 1976). In these experiments, however, the concentration of each of the six metals was 1 mg 1- ~ of medium.
the experimental fish. Twenty four 21 Pyrex dishes each containing 1 1 aged tapwater and 200g Ballotini spheres (2-4 mm diameter) were placed at 25°C in constant light with a non-reflective cloth between each dish. The dishes were divided into two sets of 12 and each set into six pairs. Into each dish of one set were placed three juvenile fish (60-80 mg dry weight each) and into each dish of the second set were placed three older fish (140-160rag dry wt each). The day of commencement of the experiment was designated day 0, and all fish were fed commercial fish food ("Nippy Nip, fine grade", 9-10 mg wet wt per fish) on this day. The fish in one of each pair of dishes were then fed the same amount of fish food on days 2, 4, 6, 8, 10, 12 and 14, and tubificids (6 per fish, I0 mg approximately wet wt per fish) fed bacteria grown in the absence of heavy metals every alternate day until day 13. Similarly the fish in the second dish of each pair were fed alternatively, fish food and worms fed bacteria grown in the presence of 1 mg 1-~ of each metal. One pair of dishes in each set was used as a control, and the fish in these dishes fed commercial fish food each day, the fish in one dish being harvested on day 0 and the fish in the other being harvested on day 14. One pair of the remaining dishes from each set was removed from incubation on days, 2, 4, 7, 11 and 14, and each fish in every dish analysed for metal levels (using dry ashing followed by atomic absorption spectrophotometry of the acid extracts of the ash), after having their stomach and alimentary tract removed. Results from three replicate fish from each dish were analysed statistically (Fisher's F Test). Samples of water from each dish were also analysed for metal levels on the day of harvesting. Fish faeces were unable to be analysed due to the small amounts produced and the difficulty in collecting the faecal material. Replicate samples of the commercial fish food and the tubificid worms (both those fed bacteria with and without elevated metal levels), were analysed for metal levels before, during and after the 14 day incubation period.
Fish feeding experiments Tropical fish (Hyphessobrycon serpae) were selected as *Present address: Fisheries Research Division, P.O. Box 19062, Wellington, New Zealand. 395
RESULTS AND DISCUSSION
Eels would have been the ideal experimental animal, but availability and size precluded their use, and so tropical fish known to consume tuhificids were used instead. In initial experiments fish were fed worms with and without elevated metal levels for 2 and 4 days. There
396
F . M . PATRICK and M. W. LOUTIT Table 1. Estimates of metal levels (mR kg- 1 dry weight) in tubificids and commercial fish food fed to fish and in fish fed commercial fish food for 14 days. Levels of metal in the tank water are given as mR l - l Cr Tubificids fed bacteria grown without added metals Tubificids fed bacteria grown with added metals Young fish Day 0 Day 14 Old fish Day 0 Day 14 Commercial fish food Tank water Range of estimations
Cu
Mn
Fe
Pb
Zn
14.58"
144.44
8.47
556.11
111.15
336.5
32.25
231.08
13.67
869.25
160.41
663.7
2.40 4.81
92.40 106.46
8.68 16.14
171.32 120.19
3.59 15.45
239.9 243.5
3.15 2.82 3.12"1" ND
58.23 11.38 111.33 9.30 7.94 65.75 0.10 ND-0.02 -0.25
94.19 8.23 149.6 101.47 17.47 298.8 272.67 12.79 404.8 0.06 ND-O.06 ND-0.04 -0.18
* Average of estimates on three replicate pooled samples. t Mean of estimates on five separate samples. ND = not detected at a level of 0.02 mg1-1. were few differences in metal levels in the fish except for C r and Pb. As levels of these metals appeared higher at the end of these experiments it was decided to extend the feeding period for 14 days. The levels of metals in the worms and commercial fish food are s h o w n in Table 1, as are the levels of metals in b o t h young and old fish on day 0 and on day 14 after being fed commercial fish food only. Although the levels of metals in the commercial food were lower than in worms fed bacteria grown in the
absence of metals (except for Zn), the quantity of food ingested and the possibly greater availability of the metals in the fish food compared with the worms were sufficient to cause elevated metal levels in the fish flesh after 14 days; often to a greater degree than in fish fed alternatively commercial fish food and such worms (Table 2). F r o m the patterns of uptake of each metal by young and old fish shown in Figs. 1 and 2, there is no d o u b t that metal levels in fish fed worms con-
Table 2. Statistical analysis of estimates of metal levels in mg kg- 1 dry wt in day 14 fish fed tubificid worms containing various levels of metals Cr Young fish fed worms fed bacteria grown without metals Young fish fed worms fed on bacteria grown with metals Young fish fed Nippy Nip only Old fish fed worms fed bacteria grown without metals Old fish fed worms fed bacteria grown with metals Old fish fed Nippy Nip only % Recovery (Gorsuch, 1970)
Cu
Mn
Fe
Pb
Zn
3.02A
79.78A
8.83A
112.32A
17.67A
229.8A
5.91B
199.42B
19.99B
181.31B
36.28B
499.2B
4.81C
106.46C
16.14C
120.19A
14.38A
243.5C
2.58 D
57.20D
7.95A
92A2C
7.60C
135.3 D
9.06E
146.08E
18.50BC
144.08D
36.29B
308.2E
2.82AD
111.33C
9.30A
101.47C
17.47A
298.8E
91.4
99.8
83.8
99.4
95.8
98.3
For any individual metal, means of one letter are significantly (1%) different from means of any other letter, ~'i=.: A is different from B, C, D, E etc., but not different from A, AB, AC etc.
Passage of metals to freshwater fish copper
:hroadum
mal~nese
_
Y
"..
s
~
30
I,
ZOO
ZO
2" e " ~ - r
,oo~,~_~
•~
-
1
I
0
iron
,o, 1
o! leod
O
40 A
400
"~ 3O0
30 ~
30O
~¢200
20
200'
10
100
O
O
~' 100 I
i
i
i
~
J
~ ~
°t,t,tq,t,ot t,, fed
397
doys--~
worms off doys orrowed
Fig. 1. Estimates of metal levels in mg kg- s dry wt in young fish fed tubificid worms containing various levels of metals. • = Fish fed tubificids fed on bacteria grown without metals. • = Fish fed tubificids fed on bacteria grown with I mg 1-' of each metal. Results expressed as a mean of estimates made on each of three fish from each dish.
taining elevated levels of metals were higher than those fed either commercial food only, or the worms containing lower levels of metals. The increase in Cr and Pb in both old and young fish were particularly marked. Uptake of Zn, Pb, and to a lesser extent Fe and Cu, was greater in young than in old fish. This could be due to the older larger fish consuming less metal when expressed as a concentration because they were fed the same weight of food as the young fish. It has been shown, however, that older members of two marine species of fish contained lower levels of Cu, Fe and Zn than younger members of the same species (Cross et al., 1973), and may be due in part to different adsorption rates across the gut, or more efficient excretion in older fish.
chromium
Statistical analysis of the differences in metal levels between all fish harvested on day 14 are shown in Table 2. These differences may have been augmented by absorption of metals from the water, but absorption should have been comparable in all tanks. The water metal levels shown in Table I were daily differences occurring in all tanks irrespective of feeding regime, fish age and time. Another combination of factors which could possibly account for differences in metal levels in the fish is the inability to match the fish exactly for size, weight or metal content on day 0, and the worms analysed for metal levels were not those actually fed to the fish. Hence differences in metal levels in the fish from one tank to another, and possible differences in metal levels in the food
copper
mongonese
30 5 4
20
20O
3¸ 2
10'
1
zinc
ieod
i 20 f
11~,
~
300 200 100
I I I [
I
I I
otzt4 t6 tellotlzll,
0 days--z-(arrow.ledworms)
Fig. 2. Estimates of metal levels in mg kg- ' dry wt in old fish fed tubificid worms containing various levels of metals. • = Fish fed tubificids fed on bacteria grown without metals. • = Fish fed tubificids fed on bacteria grown with 1 mgl-Z of each metal. Results expressed as a mean of estimates made on each of three fish from each dish. WR. 12r6
C
398
F.M. P^rRtCK and M. W. Lou-rrr
fed to the fish may account for a portion of any measured metal level differences in the fish during the experiments. The fact that there were consistent, heightened metal levels in fish fed the worms containing elevated levels of metals compared with all other fish irrespective of diet, indicates that a metal-contaminated diet is a significant source of increased metal levels in fish. The increases appeared after the second day, and this may support the observation that a single dose of metals is almost eliminated or excreted in a short time, but a small residual remains in the body, becoming measurable as a significant increase only after prolonged exposure to the metal-contaminated food (Bryan, 1971). The implications of these results are interesting when considered with other findings. Several genera of bacteria from river sediments are able to accumulate small concentrations of metals present in the water to a marked degree (Patrick & Loutit, 1976). Bacterial numbers and heavy metal levels in the river under study are higher in sediments below effluent entry points than above. Certain nutrients in the effluents apparently stimulate bacterial growth rates, leading to these higher numbers in the polluted sediments (Hynes, 1960; Curtis & Harrington, 1970; Brasfield, 1972; Cole, 1973). It is likely that the small concentrations of metals in the effluents are adsorbed or absorbed by the large number of bacteria in the sediments, and hence removed from the water and prevented from dispersing. Tubificid worms, which browse through sediments for food (Brinkhurst & Chua, 1969; Brinkhurst, Chua & Kaushik, 1972) ingest these bacteria, and so take in the bound metals. These metal-enriched worms are then consumed by fish, and thus the metals are able to be passed along the food chain. Where the diet is largely of these metal-enriched tubificids, the fish will, after a prolonged period of feeding, have heightened metal levels in their tissues. Some increase may also be due to absorption from the surrounding water. The relative importance of the means of metal uptake is likely to vary according to the concentrations and forms of metals in the food, in the organisms and the water surrounding the fish. In certain rivers where effluents reduce the number of food species very markedly (Cairns, Lanza & Parker, 1972; Cairns, 1974) the surviving fish must ingest large numbers of a smaller variety of food species, which may have become heavily contaminated with pollutant metals. Acknowledoement.~---This work was supported by a grant from the Scientific Research Distribution Committee.
REFERENCES
Brasfield H. (t972) Environmental factors correlated with size of bacterial populations in a polluted stream. Appl. Microbiol. 24, 349-352. Brinkhurst R. O. & Chua K. E. (1969) A preliminary investigation of the exploitation of some potential nutritional resources by three sympatic tubificid oligochaetcs. J. Fish. Res. Bd Can. 26, 2659-2668. Brinkhurst R. O., Chua K. E. & Kaushik N. 11972) Interspecific interactions and selective feeding by tubificid oligochaetes. Limnol. Oceano.q. 17, 122 133. Bryan G. W. (1971) The effect of heavy metals Iother than mercury) on marine and estuarine organisms. Proc. R. Soc. (Lond.) B177, 389-410. Cairns J. (1974) Indicator species vs the concept of a community structure as an index of pollution. War. Re.s. Bull. 10, 338-347. Cairns J. J., Lanza G. R. S. & Parker B. C. (1972~ Pollution-related structural and functional changes in aquatic communities with emphasis on freshwater algae and protozoa. Proc. Acad. nat. Sci. Philad. 124, 79-127. Chadwick G. G. & Brocksen R. W. t1969) Accumulatton of dieldrin by fish and selected fish-food organisms, d. Wildlife Mana9. 33, 693-700. Cole R. A. (1973l Stream community response to nutrient enrichment, d. War. Pollut. Control Fed. 45, 1874 1888. Cross F. A., Hardy L. H.. Jones N. Y. &Barger R. T. (1973) Relation between total body weight and concentrations of manganese, iron, copper, zinc and mercury in white muscle of bluefish (Pomatomus saltatrix) and a batbyl-demersal fish Antimora rostrata. J. Fish. Res. Bd Can. 30, 1287-1291. Curtis E. J. C. & Harrington D. W. [1970) Effects of organic wastes on rivers. Proc. Btochem. April, 44-62. Gorsuch T. T. (1970) The Destruction of Or qanic Matter. 1st Edn. Pergamon Press, Oxford. Hynes H. B. N. (1960) The Biology of Polluted Waters. 1st Edn 202 pp. Liverpool University Press. Liverpool. Loutit M. W., Partick F. M. & Malthus R. S. [19731 The role of metal-concentrating bacteria in a food chain in a river receiving effluent. Proc. Unit'. Otago Med. School 51, 37--38. Marples B. J. (1962) An Introduction to Freshwater Lift, in New Zealand. 1st Edn. Whitcombe & Tombs. ChrLstchurch, New Zealand. Mathis B. J. & Cummings T. F. 11973~ Sclcctcd metals in river sediment, water and ammals. J. 14"at. Polhtt. Control Fed. 45, 1573 1583. Patrick F. M. & Loutit M. W. 11976) Passagc of mctal~ in effluents, through bacteria to higher organisms. Water Res. 10, 333-335. Pillay K. K. S., Thomas C. C., Sondel J. A. & Hychc C. M. (1972) Mercury pollution of Lake Eric ccosphere. Envir. Res. 5, 172--181~ Ratkowsky D. A., Dix T. G. & Wilson K. C. (1975) Mcrcury in fish in the Derwent Estuary, Tasmania. and ~ts relation to position of the fish in the food chain..4ust. J. mar. Freshwat. Res. 26, 223-231. Walter C. M., June F. C. & Brown H. G. ~1973) Mercury in fish, sediments and water in Lake Oake, South Dakota. J. Wut. Pollut. Control Fed. 45, 2203 2210.