DETERMINATION OF SEVEN HEAVY METALS IN EIGHT SPECIES OF SEA CUCUMBERS.
ABSTRACT: The concentrations of seven heavy metals including As, Pb, Cd, Zn, Cr Cu, and Mn weredetermined in eight species of sea cucumbers. Known amounts of the washed, dried and ground samples of each species were wet digested in triplicate using nitric acid and further treated with H2O2 until clear solutions were formed. The solutions were filtered using nylon filter papers and diluted with water. The metals in the solutions were determined using ICP-MS technique. The concentrations of the toxic metals such as As, Pb and Cd were found to be lower than the permitted values according to the Malaysian Food Act of 1983 and regulation of 1985 except for As in Actinopyga Lecan and that of Pb in Thelenota Ananas species. It can therefore, be concluded that all the species of sea cucumbers except the above two species found in the sea coast of Sabah are safe for human consumption and hence can be exported overseas to earn some foreign exchange.Key words: Heavy metals, sea cucumbers, ICP-MS, Sea Coast of Sabah
INTRODUCTION:Sea cucumbers are soft-bodied marine animals which are found on the sea surface. They belong to phylum echinoderm class and Holothuroidae family . In Malaysia,the sea cucumbers have great value for their medicinalproperties and also as culinary delicacies [2,3]. Sea cucumbers have high commercial value in the export industry of Malaysia (4). Sea cucumbers are collected mainly from four locations in the State of Sabah namely, Sempourna, Sandakan, Kudat and the capital of Sabah, Kota Kinabalu  in which it is sold predominantly. These creatures accumulate metals in their bodies . Previously, Hashmi et al.  reported the distribution of metals in only one species of sea cucumber i.e., Holothuria Scabra. But, now the results of seven heavy metals concentrations in eight sea cucumber species commonly consumed, are reported.Some of the heavy metals such as As, Cu, Fe, Mn and Zn are essential micronutrients but when present in excess cause toxicity, whereas lead and cadmium are well known toxic metals which create certain medical conditions when present in excessive levels in sea cucumbers and consumed by human beings . It is, therefore important for the export industry and for the local consumption to show that sea cucumbers do not contain over the permitted limits of heavy metals in their bodies especially those of the above toxic metals. Seven heavy metals were, therefore, determined in the eight species of sea cucumbers commonly found in Sabah . The results of the determination of As, Pb, Cd, Cu, Cr, Zn and Mn concentrations in these marine animals are reported in this paper.Method and Materials: Eight different species of sea cucumbers shown in Table 1 were purchased from the market in Kota Kinabalu, Sabah. These are the sea cucumbers that the majority of people consume in Sabah. Nitric acid (65%) and hydrogen peroxide (30%) as well as standard solutions of metals used for calibration were analytical grade obtained from E. Merck, Germany. De- ionized water was prepared by Millipore, France, was used for washing and dilution of the samples. The Whatman nylon filter papers 0.45m, NYL were used for the filtration purposes. Each sample was thoroughly washed with water and dried at 80oC in an oven overnight, cooled, chopped into small pieces and then ground to a fine powder following the procedure as recommended. , transferred into air tight bottles and kept in a desiccator for further use. About 2g of each sample were weighed in triplicate, decomposed with nitric acid, cooled to room temperature and further treated with H2O2 until clear solutions were formed then diluted with water and analyzed on ICP-MS Elan 9000 Perkin Elmer.  The calibration curves obtained for standard solution of each metal showed a straight line relation between concentrations and absorption values. The coefficient of determination, r2 for the standard solution of each metal gave values between 0.995-0.999 for the variation of concentrations with absorbance values. This was taken to indicate that the unknown solutions absorption values can be used for the determination of its corresponding concentrations using the straight line relation curve of each standard metal solution.
RESULTS AND DISCUSSION: Table 1 shows the results of the average values with standard deviations of metals found in the sea cucumbers.According to the Malaysian Food Act of 1983 and Regulation of 1985, the maximum levels of metals: As, Pb, Cd, Zn, Cu permitted for human consumption are 1.00, 2.00,1.00, 40 and 30 mg/g respectively.However, the values for Cr and Mn are not provided in this Act though these two metals are considered as micro nutrients . The results of Table 1 show that the value of As found in Holothuria Leueospilota and that of Cd in Thelenota Ananas exceed the permitted limits. Therefore, these two species should not be locally consumed and exported. All other species are fit for human consumption and can be exported.Table 1: Mean Concentrations of Heavy Metals in Species of Sea cucumbersIt is on the basis of the average values of different metals given in Table 1, that the two species of sea cucumbers were excluded from the consumable list. We now consider, on the basis of lowest and highest values of the metals in sea cucumbers in the following paragraph.The results for the lowest value of As (0.16 mg/g) was found in Actinopyga Lecan species and the highest (2.43) inHolothuria Leueospilota. Since the upper value was muchhigher than the permitted value, this species should be excluded from the list of exportable species of sea cucumbers. The lowest value of Pb (0.12) in Bohadachio Vitiens and the highest (0.24) in Thelenota Ananas. The highest value of lead does not exceed the permitted value. Therefore on the basis of lowesthighest values of lead, the later value is still much lower than the permitted value, it can be put in the safe list of consumable. The lowest value of Cd (0.12) was in Thelenota Anax and the highest (2.43) in Thelenota Ananas. Because the later value was much higher than the permitted value, this species should be excluded from the list of consumable species. The lowest value of Zn (7.26) was in Holothoria Edulis species and the highest (28.37) in Stichopus Vastus. The upper value of Zn is still lower than the permitted value. These two species can be included in the consumable list. The lowest value of Cu (0.75) was in Phyllophogius Spiculata species and the highest (1.35) in Thelenota Ananas. The upper value of Cu is still much lower than the permitted value. The lowest value of Cr (1.14) was in Holothoria Edulis species and the highest (3.33) in Thelenota Ananas. The lowest value of Mn (1.26) was in Holothoria Edulis species and the highest (32.67) in Phyllophogius Spiculata. The permitted values of the last two metals are not given in the Malaysian Act. On the basis of lowest-highest values, it is concluded that the same two species i.e., Holothuria Leueospilota and Thelenota Ananas should be excluded from the consumable species of sea cucumbers.
CONCLUSION: The average as well as the lowest-highest values of the determination of As, Pb, Cd, Cu, Cr, Zn and Mn concentrations in sea cucumbers were compared with the permitted values according to the Malaysian Food Act of1983 and regulation of 1985. It was concluded that two species of sea cucumbers i.e., Holothuria Leueospilota and Thelenota Ananas should not be consumed locally and exported overseas. The six other species are fit for human consumption and can be exported.
ACKNOWLEDGEMENTS: We are grateful to our chief technician, Mrs Zainab Aman for the help with ICP-MS instrument and to Universiti Malaysia Sabah for providing the research facilities in the school of Food Science and Nutrition.
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|Author:||Hashmi, Muhammad Iqbal; Thilakar, Revathi; Hussein, Muhammad Ali bin Syed; Hoque, Zahirul|
|Date:||Mar 31, 2014|
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