Analysis of trace metals (Ni, Cu, and Zn) in water, mud and various tissues of mud crab, Scylla olivacea from Setiu Wetlands, Terengganu, Malaysia

Mud crabs, belonging to the genus Scylla from the family of Portunidae are important crustaceans of the mangrove ecosystem including Setiu Wetlands, Terengganu. Scylla olivacea is one of the three species of mud crabs that are indigenous to Setiu Wetlands, and are commonly found in the nypa palm at the lagoon areas. The mud crabs samplings were done during low tides at three locations designated as A, B, and C alongside Setiu Wetlands for trace metal analysis (Ni, Cu, and Zn). Samples of water and mud at the designated sampling points were analysed for trace metals by using an Inductive Couple Plasma-Mass Spectrometry (ICP-MS) gauge. As for the mud crabs, various parts of their body (gills, hepatopancreas, and claws) were being separated prior to trace metal analysis in each of the tissue. The average concentration for Ni, Cu, and Zn in water was 6.920±0.24 µg/L, 81.280±28.70 µg/L, and 13.400±7.50 µg/L respectively. It was found that, in the mud samples, the average values of Ni, Cu, and Zn were 5.833±0.73 ug/g, 4.782±0.77 ug/g, and 17.926±2.29 ug/g. The crab tissues analysis shows that, the average values of these trace metals in gills were 4.811±1.32 ug/g (Ni), 78.482±35.37 ug/g (Cu) and 96.803±22.28 ug/g (Zn) whereas in hepatopancreas, the average values were 4.131±2.50 ug/g (Ni), 90.903±25.56 ug/g (Cu) and 166.96±30.19 ug/g (Zn). In the claws tissues, the average value of Ni (3.550±0.955 ug/g), Cu (66.235±52.30 ug/g), and Zn (170.607±12.22 ug/g). The presence of Ni, Zn, and Cu in claws of mud crabs was significantly correlated with the metal content in the mud (r in range between 0. 975 and 0.999). Zinc content in the mud was also correlated significantly with Zn content in hepatopancreas (r = 0.9205) implying that the main source for metals accumulation in tissues of mud crabs comes from the mud surrounding their burrows. The data obtained provide the current status of the trace metal contents in wild mud crabs in relation to the environmental conditions of the habitat.