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  1. 1. Journal of National Oceanographic, Atmospheric and Marine Institute ©NOAMI Vol.25, No.2, 2008 ISSN: 1027-2119 MERCURY LEVELS IN EIGHTEEN COMMONLY CONSUMED FRESH WATER FISH OF BANGLADESH A.K.M.Sharif Bangladesh Atomic Energy Commission, Dhaka-1000, Bangladesh M.Alamgir, Stanly A.Bajue and Rashed Alam Department of Physical, Environmental and Computer Sciences Medgar Evers College, CUNY, NY, U.S.A. Abstract: Concentrations of mercury in edible portion of some commonly consumed fresh water fish,namely, Mystus vitlatus, Lates calcarifer, Penaeous monodon, Clarias batrachus,Heteropneustes fossilis,Clarias batrachus, Awaous guamensis, Labeo bata, Notoperus notopterus,Channas triatus Eutropichtys vacha, Channa punctaus, Devario devario, Hypophthalmichthys molitrix, Chanos chanos, Stipnna phasa, Cteneopharyngodon idella and Wallago attu were determined by radiochemical neutron activation analysis (RNAA). These results were found to range from (0.188-0.475) µg g-1 on dry weight, where nine species had mercury concentration, (0.188-0.295) µg g-1, six ,(0.307-0.378 µg g-1 and the rest three, (0.445-0.475) µg g-1 , based on the average values of 18 species of fish. The total average value of all fish samples is 0.315 µg g-1. The results were found to agree well with other published data on river and marine fish and within permissible level accepted internationally. Key words: Mercury, Fish, Radiochemical Neutron Activation Analysis, 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,
  2. 2. J.Nat.O.A.M.Institute Vol.25, No.2, 2008 lakes and submerged watery land. Another most important source of fish is the Bay of Bengal. Bangladesh has a large coastal belt. The Bangladeshis depend mainly on rice and fish. The rich people of Bangladesh can purchase large expensive types of fish like “Rohi”, “Katla”,”Hilsha” “Chital”,”Pangas, etc. The poor people cannot afford to purchase them. They generally purchase small types of fish, like, “Tangra”, “Shol”,”Bhetki”, 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 its 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]. Yearly, approximately, 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 safer or not to health. MATERIALS AND METHODS Samples of Collection Fish samples- Mystus vitlatus, Lates calcarifer, Penaeus monodon, Clarias batrachus, Heteropneustes fossilis, Clarias batrachus , Awaous guamensis, Labeo bata , Notopterus notopterus ,Channa striatus, Eutropichthys vacha , Channa punctaus, Devario devario, Hypophthalmichthys molitrix, Chanos 2
  3. 3. J.Nat.O.A.M.Institute Vol.25, No.2, 2008 chanos, Stipinna phasa, Cteneopharngodon idella, and Wallago attu, were 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). 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 15 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 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 concentration 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) is shown. Average mercury concentration was observed in the level, (0.188-0.475) µg g-1 in these samples. The highest concentration (0.40-0.55) ±0.0645 µ g g-1 is found in Channa striatus and the lowest, (0.17-0.25) ±0.0435 µg g-1 in Channa punctaus . 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. 3
  4. 4. J.Nat.O.A.M.Institute Vol.25, No.2, 2008 Table 1.Mercury concentration 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) Mercury Sl.No Type of fish(Local Scientific names Mercury Mean (West Names (Bangladesh Bengal, In Bangladesh India)** 1 Batasio Mystus vitlatus (0.25-0.35)±0.042 0.295 0.20-0.60 tengana(Tangra) 2 Barra mundi Lates calcarifer (0.29-0.45)±-0.072 0.377 0.20-0.65 (Bhetki) 3 -(Bagda) Penaeus (0.24-0.40)±-0.067 0.328 0.20-57 monodon 4 -(Magur) Clarias batrachus (0.28-0.42)±-0.059 0.358 0.41-0.55 5 Stinging Heteropneustes (0.40-0.50)±0.042 0.445 0.36-0.47 catfish(Shingi) fossilis 6 Walking catfish Clarias batrachus (0.0.20-0.30)±0.435 0.258 0.20-0.40 (Koi) 7 -(Bailla) Awaous (0.27-0.40)±0.464 0.34 0.37-0.69 guamensis 8 Bata (Bata) Labeo bata (0.25-0.30)±0.024 0.283 0.20-0.24 9 -(Pholi) Notopterus (0.28-0.43)±0.065 0.373 0.39-0.64 notopterus 10 Snakehead murrel Channa striatus (0.40-0.55)±0.0645 0.475 0.52-0.79 (Shol) 11 -(Bacha) Eutropichthys (0.20-0.37) ±0.069 0.28 0.20-0.41 vacha 12 Spotted snakehed Channa punctaus (0.15-0.25) ±0.0435 0.188 0.20-0.71 (Taki) 13 Sind danio(Baspata) Devario devario (0.20-0.30)±0.044 0.243 0.20-0.72 14 Silver crap(Silver Hypophthalmichthys (0.20-0.26)±0.022 0.23 0.20-0.28 crap) molitrix 15 -(Lyata) Chanos chanos (0.17-0.30) ±0.060 0.213 0.20-0.47 16 Gangetic hairfin Stipinna phasa (0.35-0.55)±0.092 0.45 0.98-1.09 anchovy(Phyasa) 17 Grass crap(Grass Cteneopharyngodon (0.28- 0.35)±0.034 0.308 0.32-0.47 crap) idella 18 Wallago (Boal) Wallago attu (0.18-0.25)±-0.034 0.223 0.21-0.25 Average: 0.3148 µg g-1 Range :( 0.15-0.55) µg g-1 4
  5. 5. J.Nat.O.A.M.Institute Vol.25, No.28 **Mercury in Fish: A Global Health Hazard, Mercury Policy Project, pp 1-50. ZeroMercury, February 2009 (Edward Groth III, PhD, Groth Consulting Services, Pelham, NY, USA _____________________________________________________________________________________ Figure 1 0.5 0.45 0.4 0.35 Amt. Of Hg (µgg^-1) 0.3 0.25 0.2 0.15 0.1 0.05 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Serial Number of fish Though the liver and kidney are usual organs for major concentrations of metals but mercury is accumulated at higher level only in the muscle of fish [15] and in its case biomagnification 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 fish. 5
  6. 6. J.Nat.O.A.M.Institute Vol.25, No.2, 2008 Estimation of Dietary Intake of Hg in Bangladesh Average concentration of Hg found in the samples fish of fresh water origin is (0.315±0. 0.0513) 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 (1.90-3.15) µg person-1 day-1 . This value is well below the maximum acceptable level for human being (0.5 µg g-1 wet weight) [15-20]. Similarly, 70 g dry fish per week would result in an intake of 22.05 µg of Hg which is also below the tolerable limit (0.7 mg (kg)-1 body of an about 70 kg man as suggested by the report [20]. 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 Mr.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 [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. 6
  7. 7. J.Nat.O.A.M.Institute Vol.25, No.2, 2008 [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] Chaudhuri, N. (1980) Increasing danger of mercury pollution, 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) Mercury levels in six species of Australian Commercial fish, 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. 285-309. [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.L., and Sharp G.D.(1973), Mercury in Tunas: A Review, Fish Bull., 71, pp. 603-612. [16] FAO/WHO (1972-1987), Joint FAO/WHO Expert Committee on Food Additives, Reports 505, 631, 683,696 and 751. World Health Organization, Geneva. [17] Nauen, C.E. (1983), Complication of legal limits for hazardous substances in fish and fishery products, FAO Fish Cric., 764. [18] 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. [19] Hakanson, L., Nilsson, A. and Andersson, T. (1988), Mercury in fish in Swedish Lakes, Environ Pollut., 49(2), pp. 145-162. [20] WHO (1976), Environmental Health Criteria, I-Mercury, WHO, Geneva 7