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MERCURY CONCENTRATIONS IN TWELVE COMMONLY CONSUMED FRESH WATER FISH OF BANGLADESH

MERCURY CONCENTRATIONS IN TWELVE COMMONLY CONSUMED FRESH WATER FISH OF BANGLADESH

INTRODUCTION

Bangladesh is a country through which a large number of big rivers, the Meghna, the Bhramaputra, the Surma, the Karnaphuli and the Padma flow. A good number of small rivers also flow through this country. Basically, it is a country of big and small rivers. Besides these rivers, there are lots of “Bills”, “Howors”, “Khals”, ponds, water reservoirs, lakes, and submerged lands where water exists throughout the year in this country.

Fish is collected from these big and small rivers. Fish is also available in the “Bills and Howors”,”Khals”, lakes and ponds. Besides these sources, fish is produced and nourished in big water reservoirs, ponds, lakes and submerged watery land.  Another most important source of fish is the Bay of Bengal. Bangladesh has a large coastal belt.

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The Bangladeshis depend on rice and fish. The rich people of Bangladesh can purchase large types of fish like “Rohi”, “Katla”,”Hilsha” “Chital”,”Kalibasu”, etc. The poor people cannot afford to purchase them. They generally purchase small types of fish, like, “Tangra”, “Taki”,”Bele”, etc. Sometimes and occasionally, they purchase medium sized fish varieties, low in price. In order to evaluate the concentration of mercury in small and medium size fish specimens, this work was undertaken.

Mercury is one of the most toxic elements detrimental to man and other animals. Due to adverse effects on them, much attention has been focused on the measurement of mercury in environment. The presence of high concentration of mercury in river and marine organisms is well–documented [1-4]. Investigations on  heavy metals in aquatic  ecosystems have recently got much attention and interest  in Europe, Australia and North America, but few studies are available about the level of contamination, particularly that of Hg in different types of fish from rivers, and of the Bay of Bengal. The reports [5-7] gave good information on level of few metals including Hg in some river and marine fishes of the Bay of Bengal.

In the rivers and sea, mercury originates mainly from coal burning, weathering, sewage disposal and industrial wastes. From discharges of Chloro-alkali industries of Chittagong and Sylhet, through the rivers, the Karnaphuli and the Surma, mercury discharges to the Bay of Bengal. Nearly, one hundred and eighty tons of Hg is introduced every year into the Indian environment alone [8]. Every year nearly, 2.4 billion tons of sediments [9-11] are carried by the river system of Bangladesh. Thus the high mercury level in the Bay of Bengal may be due to direct disposal of industrial wastes or solid wastes dumped into rivers of the subcontinent, which ultimately comes to the Bay of Bengal. .

An  estimated value of Hg content in daily diet varies from 5 to 20 mg and may reach up to 100- 300 mg in coastal areas [7]. Fish can accumulate both organic and inorganic mercury in its metabolic system. Various species of fish are the natural sources of Hg to man [12]. The total intake of Hg from other sources is negligible [13-14].

Inhabitants near to the coastal areas are directly or indirectly dependent on the resources of the sea. The main objective of the present study is to know the mercury level in the commonly consumed fresh water fish of rivers of Bangladesh, and to compare the results whether they are safe or not to health.

MATERIALS AND METHODS

Samples of Collection : Fish samples- Chitala chitala, Cirrhinus cirrhous, Ctenophryngodon idella, Colisa fasciata, Cyprinus carpio carpio, Glossogobius giuris, Hypophthalmichthus michthys molitrix, Labeo boggut, Monopterus cuchia, Ailia coila, Labeo calbasu and Channa punctalawere collected from different fish markets of Dhaka, Commilla, Chandpur, Chittagong,Sylhet, Rajshahi and  Khulna. Special precautions were taken during their collection and preservation in containers so that these specimens were kept in good condition. Their weights and sizes were recorded. The samples were cleaned and washed with deionized water. Only the flesh samples after removal internal organs, head, skin and tails, were taken out from the body. These samples were sun-dried. The dried samples were then chopped into pieces with the help of a stainless steel knife (steam-cleaned).

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Only the edible muscle tissue samples were used for analysis.  The sample pieces were dried at 105-110oC in an oven until a constant weight was obtained (dry weight) .The dried samples were ground, sieved and thoroughly mixed in a stainless steel rotating drum for 100 hours to produce a homogeneous powder .These powder samples were finally preserved in clean and dry  polythene bottles prior to analysis.  All the chemicals and reagents were of analytical grade.

Irradiation

Portions of the samples (200-300 mg each) were thermally sealed in polyethylene bags and  irradiated for 18 hours along with a known amount of MA-A-2™, the fish flesh homogenate standard of IAEA (International Atomic Energy Agency)  in the TRIGA MARK II  reactor at AERE, Savar, Dhaka at a flux of about (0.5 to 1.0) x1012 n.cm-2.s-1.

Radiochemical Separation

The process for dissolution and chemical separation was the same as the process described elsewhere [7].

Counting

The samples and the standard were counted on a 125cm3 HPGe detector connected to a 4096 pulse height analyzer  PCA II MCA card. The energies (in keV) chosen for the evaluation of the peak areas were                                                            [197Hg: t1/2(65 h)] Eγ = 69 and 77.3 keV. The minimum detection limit was one nanogram for mercury

for the total sample volume. The counting errors at the detection limits were around 7% .The blank polyethylene bag did not show any measureable mercury content.

Accuracy and Precision

Experiments were initially carried out using a radioactive tracer and the corresponding carrier to evaluate the recovery. The accuracy of the method was evaluated by analyzing the homogenate fish flesh (IAEA)

Standard  Reference Material, MA-A-2 (TM). The mercury concentration was 0.45± 0.06-µg g-1 and this result is in good agreement with the IAEA certified value (0.47±0.02 µg g-1).

RESULTS AND DISCUSSION

In the Table 1, Mercury concentrations in some commonly consumed fresh water fish of Bangladesh and their comparison with those available in West Bengal (India) (µg g-1 dry weight basis) are shown. Average mercury concentration was observed in the level, 0.359± 0.063  µg g-1 in these samples. The highest concentration (0.40-0.65)±0.108 µg g-1 is found in Glossogobius giurisand the lowest, (0.22-0.28)±0.026µg g-1in Cirrhinus cirrhous . It is observed that the level of Hg in fishes of fresh water origin is much lower than that in other countries. A relationship between the amount of mercury (µg g-1) and the number of fishes is shown in Figure 1.

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Table I was deleted.

Figure1.was also deleted

Though the liver and kidney are usual organs for major concentrations of metals but mercury is also accumulated at higher level only in the muscle of fish [15] and in its case biomagnifications occurs through food chain.

The permissible limit varies a little bit from country to country. One proposed by FDA (Food and Drug Administration) of the United States is 500 ppb. The mercury level in the present investigation is much lower than this value. The trend of increasing concentration of Hg with increases in size of fish indicates long time of its conservation in water.

Estimation of Dietary Intake of Hg in Bangladesh

Average concentration of Hg found in the samples fish of fresh water origin is 0.359± 0.063 µg g-1 .   Assuming maximum average of fish consumption person-1 day -1 is 6-10 g dry fish for various areas of Bangladesh, the maximum Hg intake through fish is estimated to be (2.54-3.59) µg   person-1 day-1 . This value is well below the maximum acceptable level for human being (0.5 µg g-1 wet weight) [16 – 20] Similarly,70 g dry fish per week would result in an intake of 25.13 µg of Hg which is also below the tolerable limit (7.0 mg kg-1 body wt.day-1 ) of an about 70 kg man as suggested by[20].

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CONCLUSION

The level of mercury reported here may be taken as a convenient baseline for determining future pollution trends. Low Hg content observed in this study indicates that various types of fish are from pollution or mercury contamination and come from clean environment. So there is no danger to have these fishes for a Bangladeshi person.

Acknowledgement

The authors express thanks to Dr.K.R.Krishnamorti, Analytical Chemistry Division, Bhava Atomic Research Center, Trombay, India, for using the method, the radiochemical separation of trace metals in biological samples, used in that Laboratory

REFERENCES

[1] Akielazek, J.J.and Haines, T.A. (1981) Mercury in the muscle tissue of fish from three northern marine lakes,   Bull Environ. Contom.Toxically, 27(1), pp. 201-208.

[2] Bacci,E.(1989) Mercury in the Mediterranean, Mar.Pollute.Bull. , 20(2), pp.59-63.

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[3 ] Bjorklund, I., Borg, H. and Johanssson, K. (1984)  Mercury in Swedish lakes, its regional distribution and  causes, Ambio., 13(2), pp 118-121

[4] Lee,Y.H. and Hultberg, H. (1990), Methylmercury in some Swedish surface waters, Environmental Toxicology and Chemistry, Vol. 9, pp.833-841.

[5] Sharif, A.K.M., Mustafa, A.I., Amin.N.M. and Safiullah,S (1991),Trace metals in tropical marine fish from the Bay of Bengal,  Sci .Total Environ., 107, pp. 135-142.

[6] Sharif, A.K.M., Mustafa,A.I., Mirza, A.H. and Safiullah,S.(1993a),Trace element concentrations in ten species of freshwater fish of Bangladesh,  Sci. Total Environ., 138, pp. 223-234.

[7] Sharif. A.K.M., Alamgir, M., Krishnamoorty, K.R. and Mustafa, A.I. (1993b), Determination of arsenic, chromium, mercury, selenium and zinc in tropical marine fish, Nucl.Chem.170, pp.299-307.

[8] Chaudhury, N. (1980) , Ind..Exp., 48, p 9.

[9] Holeman, J.N. (1968), The sediment field of major rivers of the world, Water Resources research, Vol.4 (4), pp. 737-747.

[10] Coleman, J.M. (1969) , Bhrahmaputra Rivers: Channel Processes and sedimentation, Sedimentary Geology, Vol. 3(2-3), pp. 129-238.

[11] Khan.H.R. (1978) A Study of Water Resources Development Activities in Bangladesh. A report for Ford Foundation, Dhaka, p. 87.

[12] Chovjka,R. and Williams, R.J. (1980) Aust.J.Mar.Fresh water Res., 31, pp. 469-473.

[13] Clarkson, T.W .(1984), Mercury, In: J.O.Nriagu (ed.) Changing Metals Cycles and Human Health, Springer Vertag, Berlin, pp. 258-309.

[14]  Turner, M.D., March, D.O., Smith, J.C., Inglics, J.B., J.B., Clarkson, T.W., Rubio, C.E., Chirboga, J. and Chiriboga, C.C.(1980), Methylmercury in population eating large quantities of marine fish, Arch.Evviron.Health., 35, pp. 367-370.

[15 ] Peterson, C.L., Klawe,W.K. and Sharp G.D.(1973), Fish Bull., 71. pp. 603-612.

[16] Hakanson, L., Nilsson, A. and Andersson, T.(1988), Mercury in fish in Swedish Laeks, Environ Pollut., 49, pp. 145-162.

[17] FAO/WHO (1972-1987), Joint FAO/WHO Expert Committee on Food Additives, Reports 505, 631, 696 and 751. World Health Organization, Geneva.

[18] Nauen, C.E.(1983) , Complication of legal limits for hazardous substances in fish and fishery products, FAO Fish Cric., 764.

[19] Denton, G.R.W. and Burdon-Jones, C (1996), Trace  metals in fish from Great Barrier Reef. Marine. Pollute. Bull. 30(5), pp. 201-209.

[20] WHO (1976) , Environmental Health Criteria, I-Mercury, WHO, Geneva.

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