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Articles by C.K. Yap
Total Records ( 5 ) for C.K. Yap
  C.K. Yap and S.G. Tan
  It had been documented through electrophoretic studies that allozyme polymorphisms of bivalve populations are affected by heavy metal stress. In the present laboratory study, by using P. viridis as a test organism, the results indicated that changes in the enzymes GOT, EST and ME were due to Zn stress which are complemented by reductions of filtration rate and condition index. However, it is not yet known for sure whether the enzymes GOT, EST and ME are inducing behavioural and other changes in P. viridis. This is because of the possible subtle interactions could occur between different environmental stresses.
  G.H. Ong , C.K. Yap , M. Maziah and S.G. Tan
  The objective of this research was to determine the metal accumulation of C. asiatica collected from 13 sampling sites from Peninsular Malaysia and its safety for consumption by the public in Malaysia. Centella asiatica plants were collected (or bought) from 13 sampling sites (9 from the wild and 4 from markets) between May and June of 2010. The leaves, stems and roots of C. asiatica were determined for Cadmium, Copper, Iron, Nickel, Lead and Zinc. Generally, Iron accumulation was the highest followed by Zinc, Lead, Copper, Nickel and Cadmium. For all metal accumulations, roots showed the highest level, followed by leaves and stems. Plants from sampling sites in Seremban, PPauh and Butterworth were higher in metal accumulation due to nearby activities such as industrial area and highway. When compared to the reference values from Recommended Dietary Allowance, Daily Dietary Intake, Tolerable Upper Intake Level and maximum level intake without detriment to health, all samples from the 13 sampling sites had metal levels which were within or lower than the safety levels or maximum permissible level for human consumption. Therefore, our results showed that Centella asiatica was safe to be consumed for all purposes especially for medical treatment of various illnesses.
  C.K. Yap , A. Ismail and S.G. Tan
  The concentrations of Cu, Cd, Pb and Zn were analysed in different parts (root, byssus stem, byssal thread and attachment plaque) of the byssus of green-lipped mussel Perna viridis. Foot and total soft tissue were analysed for comparison. Heavy metal distributions in different byssus portions were observed. The attachment plaque recorded the highest levels of Cd (2.22 μg g-1), Cu (17.48 μg g-1), Pb (11.92 μg g-1) and Zn (73.94 μg g-1) when compared to the other parts of byssus, foot and total soft tissue. Different protein composition is believed to be the reason for the different heavy metal levels found in the different parts of the byssus.
  C.K. Yap , A. Ismail and S.G. Tan
  The geochemical partitioning of copper (Cu) in surface sediment of two sampling cruises from the Straits of Malacca have been studied. The results show that the total concentrations of Cu in sediments ranged from 2.48 to 11.95 μg g‾1 and 2.59 to 13.3 μg g‾1 for the first and second sampling cruises, respectively. Nonresistant fractions (EFLE, acid-reducible and oxidisable-organic) covered 60.43% (first cruise) and 46.21% (second cruise) of total Cu concentration in the sediments. This indicated that although the total Cu concentration in sediments were relatively low, the geochemical study revealed that about 50% of the total Cu found in the sediment could be due to anthropogenic inputs besides natural origins. Among this nonresistant fractions, the oxidisable-organic fraction contributed about 81-86%.
  C.K. Yap , F.B. Edward , R.A.A. Emila , F.I. Ainey , A. Ismail , S.G. Tan and Y. Sharizat
  The guppy fish, Poecilia reticulata and the lake surface sediments were collected from the Serdang Lake in August 2005. Both the fish and the sediment samples were analyzed for Cu, Cd, Pb, Zn and Ni. The ranges of metal concentrations (μg g-1 dry weight) in the fish were 0.160-11.1 μg g-1 for Cu; 64.6-174 μg g-1 for Zn; 0.400-4.03 μg g-1 for Cd; 3.27-12.1 μg g-1 for Ni and 19.5-50.9 μg g-1 for Pb. In the sediment, the ranges of metal concentrations were 1.97-62.1 μg g-1 for Cu; 31.6-274 μg g-1 for Zn; 1.92-3.17 μg g-1 for Cd; 60.2-94.8 μg g-1 for Ni and 3.23-42.1 μg g-1 for Pb. It was found that the concentrations of Zn was the highest found in both fish and sediment samples, followed by Pb, Cu, Ni and Cd. The similar pattern of heavy metal occurrence was found in the fish and in the sediment, indicated that the fish could be used as a potential biomonitor for metal contamination in the freshwater ecosystem. Since P. reticulata are widely distributed in lakes and in almost all of the urban drainage, this fish species is a very potential biomonitor of heavy metal bioavailabilites in the polluted freshwater ecosystem of Malaysia.
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