A STUDY OF THE LEVELS OF SOME SELECTED HEAVY METALS IN RIVER AND SEA WATERS AND MARINE BIOTA FROM COASTAL WATERS AROUND SINGAPORE

Abstract

Increasing concern about toxic heavy metal pollution in the environment has stimulated many investigations into the effects of heavy metals on the environment and their distribution in the marine biological materials, rivers and seas. Samples of eleven different species of popular seafood including fishes 1 crabs, prawns, squids and bivalves together with three species of marine algae have been collected from coastal waters around Singapore. All the samples of marine biota were prepared for analyses by dry ashing method and the residues were dissolved in nitric acid and then analyzed by atomic absorption spectrophotometry (AAS) for ad, Co, Or, au, Fe, Mn, Ni, Pb and Zn. Samples of marine biota tissue for mercury analysis were digested with cone. sulfuric acid at 50°- 60° overnight, The mercury present in the samples was oxidized to mercury (II) ion with potassium permanganate and nitric acid, Hydroxylamine hydrocholoride was then added to remove the excess permanganate, Mercury (II) ion was reduced to mercury (o) with stannous chloride and its vapor equilibrated with air and then determined by flameless AAS. Water samples from ten main rivers or canal and various parts of coastal areas around Singapore have also been collected and analyzed. The levels bf soluble heavy metals such as Cd, Co, Cu, Fe, Mn, Ni, as well as Pb and Zn in water samples were analyzed by using chelation and followed by extraction method. The metals were chelated by the addition of ammonium pyrrolidine dithiocarbamate to filtrates of water samples at appropriate pH values. The chelates were extracted by methyl isobutyl ketone-cyclohexane mixed solvent, then the organic extracts were analyzed by AAS. The application of the flameless technique to the determination of mercury in water samples is also briefly described. Recoveries of the respective metals added to some original samples were satisfactory. Background contamination problems and procedural precaution were also discussed in this thesis. The analytical results showed that levels of harmful heavy metals in marine biota, river and sea waters, with a few exceptions, were generally low.