Levels of Lead and Cadmium in 17 Species of Fresh Water Fish of Bangladesh
Levels of Lead and Cadmium in 17 Species of Fresh Water Fish of Bangladesh
INTRODUCTION
In recent years much attention has been focused on concentrations of some toxic metals in freshwater fish and other aquatic organisms [1-5]. Proper interest has understandably been mainly directed towards commercial and edible species since high concentrations levels of some elements can be hazardous to health. It is also being suggested that some aquatic organisms may provide useful means of monitoring such elemental concentration levels in surface waters and their impact on the aquatic environment [6].
The main sources of lead in the aquatic environment are leaded gasoline, and contributions from mining areas, the latter being typical point sources with a low ionization coefficient.
J.Nat.O.A.M.Institute Vol.26, No.2, 2009
On the other hand, cadmium is also easily volatilized at the operating temperatures of common industrial processes. Much of the cadmium in the atmosphere results from incineration of ferrous scrap fossil fuel combustion, tire wear and metallurgical processes [7].
The number of rivers, canal and stream in Bangladesh is about 230 with a total length of about 24,135 km and occupying a riverine area of about 9,384 sq.km [8].
In Bangladesh, fish production was about 814,685 metric tons in 1987. Inland fishery contributed nearly 73% of total production and supplies 80% of the animal protein requirement of the country. Fish is now an important source of protein (~20%) for the general population and also represents a lion’s share of foreign exchange by its export to other countries. In addition, it is also rich in essential minerals and vitamins, and low in saturated fats, making it an ideal food.
Bangladesh is a country which has no baseline nor has a list of maximum permissible concentration of toxic elements in water stated in a national legislation. The determination of cadmium and lead has yet been carried out for fresh water fishes consumed in Bangladesh. Cd and Pb levels in a good number of commonly consumed fresh water fishes collected from different areas of Bangladesh have been reported in this paper, which is believed to be a great help for fish trade as well as health and safety of the people.
Materials and method
Sample collection
Fish samples – Tenualosa ilisha, Pangasius pangasius, Labeo bata , Neopropius atherinoides, Otolithoides pama, Puntius sarana, Ompok pabda, Sicamugil cascasia, Clarias batrachus, Heteropneustes fossil, Labeo rohita, Gudusia chapra, Mystus vittatus, Awaous quamensis ,Eutropichthys vacha , Notopterus notopterus and Mastacembelus armatus were obtained from different fish auction places, namely, Soari Ghat,Dhaka; Gumati, Comilla, ; and Turag, Tongi; Chandpur,Comilla; Sumanganj;Khulna and Rajshahi. The fish species were identified by their scientific names with the help of the Department of Fisheries of Ministry of Fisheries and Livestock. During this study about 50 samples of each of fishes were collected, each sample weighing about 0.1 to 500 gm. Kachki, Batashi and Darkina are small in size, each weighing about 0.2 to 2 gm, where other varieties of fishes are much bigger in size having variable weights ranging from 100 to 500 gm depending on the type and age. The samples were cleaned and washed with distilled water. The flesh parts of fishes were taken out from their bodies. These samples were dried in an oven at 65oC for 48 hours discontinuously. The dried samples were powdered and homogenized. The sample powders were dried at 105oC in an oven until a constant weight was obtained (dry weight). The sample powders were finally preserved in clean and dry polythene bottles prior to analysis.
Chemical analysis
2 gm of the fish powder was added to a mixture of concentrated nitric acid (10 ml), 66% perchloric acid (5 ml) and de-ionized water (5 ml) in a Teflon vessel. The vessel was placed in a sealed stainless container and heated at 150oC for 2 h in an oven. After cooling, the vessel was removed and the sample solution transferred to a Teflon beaker containing 25 ml de-ionized water. The resulting solution was further heated at 100oC for 15-20 min, and filtered; the filtrate was diluted to 100 ml with de-ionized water. An analytical blank was prepared in a similar manner without the sample. All glassware was carefully cleaned with hot nitric acid followed by thorough rinsing with de-ionized water before use. The sample weight, acid proportions and final volumes are given in Table 1.
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The aqueous digest was analyzed directly using a Pye Unicam SP-2900 Flame Atomic Absorption Spectrophotometer with electrodeless discharge lamp (Pb and Cd). Standards were prepared in an 0.1 N perchloric acid. The analytical procedure was checked using standard reference material MA-A-2™, Fish Flesh Homogenate, provided by the IAEA (Vienna). Results of the analysis are in given Table 2. Our results are in excellent agreement with the certified values. Sensitivity and detection limits for the metals concerned, by the AAS are shown Table 3.
3. RESULTS AND DISCUSSION
Table 4. Shows that the levels of lead and cadmium for 17 varieties of fresh water fish. Data are expressed in micrograms per gram on a dry weight basis. In Figure 1, the relationships, between the serial number of fish specimens and the amounts of lead, Figure 2, serial number of fish and the amount of cadmium and Figure 3,serial number of fish and amounts of Pb and Cd are shown respectively.
Out of the seventeen fresh water fish species, two (Kachki and Batashi) were prepared with the gut while the fifteen varieties were prepared without gut for their analysis.
4(four) Tables are deleted.
1 (one) Figure is deleted.
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J.Nat.O.A.M.Institute Vol.26, No.2, 2009
Although some investigators prefer to determine lead and cadmium etc., in the liver of fish [9], the present investigation was carried out in the edible tissue only as the dietary habit of the people of Bangladesh excludes liver of fishes. The levels of Pb vary between 0.29 µg g-1 in Mystus vittatusand 10.055 µg g-1 ,Sicamugil cascasisa (Kachki) and those of Cd , between 0.03 µg g-1, Mastacembelus armatus and 0.16 µg g-1, Ompok pabda (Pabda).These variations are likely to be due to the living nature and dietary habits of the different species of fish. Shorputi is the bottom living fish. Tenualosa ilisha (Ilish) is a fish of migrating nature. This fish is largely available in the river, the Meghna at the mouth of the Bay of Bengal. The levels of Pb and Cd in this fish are 1.64 and 0.10 µg g-1. In two medium size popular fish species, Labeo rohita (rui) and Pangasius pangasius (Pangas), Pb levels range between 1.25 and 3.09 µg g- 1 and those of Cd, 0.09 and 0.13 µg g-1. Some of fish species, such as Shorputi, Pabda, Poa, Bata ,Bacha ,Baim,Pholi generally live at the deeper parts of rivers, and water resources.. These species are in almost continuous contact with sediments, which may the sources of contamination, and also hibernate in them during the whole year. The rest other species, like Koi, Singh, Chapila, Tengra,Bailla are the shallow water fishes, which may gather contaminants from muddy water. Dietary difference between these fish species and the other fish samples is unlikely to be the source of higher metal.
There are very few data from Bangladesh, to compare the levels of metals found in fishes in this study. Concentrations of metals in all varieties of fish were similar to those reported elsewhere [10-11]. Lead and cadmium levels in all fishes examined range from 0.56 µg g-1 to 0.53µg g-1 and 0.019µg g-1 to 0.18µg g-1 respectively on wet basis, if one considers the conversion factor of 4.8-5.0 for fresh weight. Concentrations at or close to these values have been reported for tropical species from other areas of the World [12-21].
The mean concentrations of lead and cadmium in fish are 2.46 µg g-1 and 0.094 µg g-1 respectively. Taking 6-10 g of fish as the maximum consumption per person per day for Bangladesh, it is estimated that the average intakes of lead and cadmium through fish are 14.8 µg g-1 to 24.6 µg g-1 and 0.56 µg g-1 to 0.94 µg g-1 respectively. These values of lead and cadmium are much below the provisional tolerable intakes by human being of total lead (7.1 µg kg-1 body wt. day-1) and cadmium (1.102 µg kg-1 wt.day-1) [22-25].
The data may be taken as a convenient base line against which any further pollution trends could be measured and evaluated. More comparative data from a range of sites in Bangladesh are, however, required for the assessment of pollution with lead and cadmium.
REFERENCES
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6. A.Preston., D.F.Jefferies., J.W.R.Dutton., B.R.Harvey and A.K.Steele., British Isles Coastal Waters –The concentrations of selected heavy metals in seawater, suspended matter and biological indicators pilot survey. Environ. Pollut. 3, pp 69-82 (1972)
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11. A.H.Khan, M.Ali, S.K.Biswas and D.A. Hadi,Trace elements in marine fish from the bay of Bengal, Sci Total Environ., 61, 121 (1987).
12. A.V.Holdden and G.Topping, Proc.R.Soc. Edinburgh,Occurrence of spedific pollutants in fish in the Forth and Tay estuaries, Sect.B, 71, 189 (1972)
13. I.J.Eustance,Zinc,cadmium,copperand manganese in species of finfish and shellfish caught in the Derwent Estuary, Tasmania, Aus.J.Mar. Fresh water Res; 25, 209 (1974)
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