2. J.Nat.O.A.M.Institute Vol.24, No.2, 2007
and the Surma, mercury comes to the Bay of Bengal. Nearly, one hundred and eighty tons of Hg is
introduced every year into the Indian environment alone (Chaudhury, 1980). Yearly 2.4 billion tons of
sediments (Holeman, 1968; Coleman, 1969 and Khan, 1978) 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 by rivers of the subcontinent.
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 (Sharif et al., 1993b). Fish can accumulate both organic and inorganic mercury in its
metabolic system and they are the natural sources of Hg to man (Chovjka and Williams, 1980). The total
intake of Hg from other sources is negligible ( Clarkson, 1984; Turner et al., 1980).
People living 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 level of mercury in the tropical fresh water fishes of
rivers of Bangladesh ,and to compare whether it is safer or not health.
MATERIALS AND METHODS
Samples of Collection
Fish samples of Tenualosa Ilisha,Pangasius pangasius, Septinna phasa, Neopropius
atherinoides,Otolithoides pama , Puntius sarana,Ompok pabda, Sperata aor, Clarias batrachus,
Heteropneustes fossil ,Labeo rohita, and Catla catla were collected from different fish markets of Dhaka,
Commilla,Chandpur,Chittagong,Sylhet,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 demineralized 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 samples
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 analysis
polythene bottles prior to analysis. All the chemicals and reagents were of analytical grade.
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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 n.cm-2.s-1.
Radiochemical Separation
The process for dissolution and chemical separation was the same as our process described
elsewhere (Sharif et al .1993b).
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
is in good agreement with the IAEA certified value (0.47±0.02 µg g-1).
RESULTS AND DISCUSSION
The concentration of mercury found in the samples of fish has been shown in Table 1. Mercury
concentration was observed at the level 0.243 to 0.675 µg g-1 in these samples. The highest concentration
(0.582-0.836±0.127 µ g g-1) is found in Setipinna phasa and the lowest (0.250-0.260±0.004 µg g-1)
Neopropius atherinoides. It is observed that the level of Hg in fishes of fresh water origin is much lower
than that in other countries. A. comparison of mercury concentrations in some fresh water fish available
in Bangladesh and West Bengal (India) (µg g-1 dry weight basis) is shown in Table 2. A relationship
between the amount of mercury (µg g-1) and the number of fishes is shown in Figure 1.
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5. J.Nat.O.A.M.Institute Vol.24, No.2, 2007
Table 2.Comparison of Mercury concentrations in some fresh water fish available in Bangladesh and
West Bengal (India) (µg g-1 dry weight basis)
Type of fish(Local Scientific names Mercury Mercury
Names (Bangladesh) (West Bengal,
In Bangladesh and India) India**
1. Hilsa Shad
(Ilish) Tenualosa ilisha 0.334-0.442±0.052 0.55-0.83
2. Yellow tail catfish
(Pangas) Pangasius pangasius 0.355-0.426±0.027 0.22-0.52
3. Gangetic hairfish
Anchovy(Phasa) Setipinna phasa 0.582-0.836±0.127 0.96-1.09
4. Indian potasi Neopropius
(Batashi) atherinoides 0.250-0.260±0.004 0.25-0.42
5. Pana croaker
(Poa) Otolithoides pam 0.277-0.342±0.027 0.20-0.35
6. Olive barb
(Shorputi) Puntius sarana 0.22-0.44±0.11 0.48-0.60
7. Pabo catfish
(Pabda) Ompok pabda 0.230-0.264±0.015 0.20
8. Long-whiskered
Catfish (Ayre) Sperata aor 0.267-0.875±0.304 0.20-1.02
9. Walking catfish
(Koi) Clarias batrachus 0.246-0.344±0.042 0.28-0.40
10. Air breathing fish
(Singh) Heteropneustes fossil 0.288-0.320±0.016 0.20-0.47
11. Ruhu
(Rui) Labeo rohita 0.214-0.448±0.167 0.20-0.59
12. Catla
(Katol) Catla catla 0.250-0.340±0.045 0.20-0.59
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________________________________________________________________________________
**Mercury in Fish : A Global Health Hazard, Mercury Policy Project, pp 1-51
ZeroMercury, February 2009 (Edward Groth III, PhD, Groth Consulting Services, Pelham, NY, USA)
_________________________________________________________________________________
Figure 1
0.8
0.7
0.6
Amt. Of Hg (µgg^-1)
0.5
0.4
0.3
0.2
0.1
0
1 2 3 4 5 6 7 8 9 10 11 12
No. 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 (Peterson et al., 1973) 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 fish.
Estimation of Dietary Intake of Hg in Bangladesh
Average concentration of Hg found in the samples fish of the Bay of Bengal is 0.343±0.525 µg g-1.
Assuming Maximum average of fish consumption person-1 day -1 is 6-10 g dry fish for Chittagong and
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7. J.Nat.O.A.M.Institute Vol.24, No.2, 2007
coastal areas of Bangladesh, the maximum Hg intake through fish is estimated to be 2.06-3.43 µg
person-1 day-1 . This value is well below the maximum acceptable level for human being (0.5 µg g-1 wet
weight) (WHO, 1976: FAO/WHO, 1972-1987: Nauen, 1983: Denton et al. ,1996: Hakanson et al.,1988.
Similarly, 70 g dry per week would result in an intake of 24.01 µg of Hg which is also below the tolerable
limit (0.7 mg( kg)-1 body wt.day-1 ) of an about 70 kg man as suggested by WHO (1976).
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 the Bay of Bengal has pollution free and
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.
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