Analytical and environmental studies on the marine chemistry of arsenic and some other trace metals

Maher, W.A (1980) Analytical and environmental studies on the marine chemistry of arsenic and some other trace metals. University of Southampton, Doctoral Thesis.

Abstract

Methods were developed for the measurement of total arsenic in extracts of biota and sediments, and dissolved arsenic in seawater using arsine generation and electrothermal atomic absorption spectrophotometry. With extracts of biota and sediments, a zinc column arsine generator was used. The detection limit was 2 ng/ml. and the coefficient of variation 1.7% at 50 ng/ml. Solvent extraction, ion exchange chromatography and arsine generation were combined to determine the concentrations of inorganic arsenic, monomethyl arsenic (ICU) and dimethylarsenic (DMA). With seawater,arsine was generated using sodium borohydride and trapped in a solution of potassium iodide and iodine. The limit of detection was 0.15 jig/L. and the coefficient of variation 3.7% at 1.6 pg/L. The method was extended to determine selenium in biological materials, but with tellurium several elements interfere severely with hydride generation. Phaeopbyta were found to have elevated arsenic concentrations relative to Rhodophyta and Chlorophyta. Only a small percentage of the arsenic in macroalgae was inorganic; the organic arsenic compound(s) presentt could be substantially degraded by digestion with nitric acid and hydrogen peroxide to DMA. Biochemical fractionation of macroalgas revealed arsenic in several fractions. The lipid soluble arsenic compounds were polar and not chromatographically identical with comWo: phospholipids. The largest amount of arsenic was isolated in the ethanol/water extracts, in which only one non-amino arsenic compound was present. The highest concentrations of arsenic were found in the biochemical fractions containing the lowest phosphorus concentration. Concentrations of selenium are generally higher in Rhodophyta and Chlorophyta. Selenium was dominantly associated with combined atinc acids and structural polysaccharides. Selected molluscs and crustaceans were examined. Higher concentntions of arsenic were found in the visceral mass and mantle tiscar c:' mussels (Itvtilus edulis) and clams (Merceneria mercenena) and the digestive and muscle tissues of crabs (Carcinus maenas and Cancer pa m=s). Arsenic in the clam was distributed between several biochemical fractions while in the crabs it was nearly entirely extracted by chloroform/methanol. The organic arsenic compounds piC.._. were only partially degraded by acid digestion to characterised inorganic and methylated arsenic species. Pelagic and estuarine sediments contained mostly inorganic arsenic, associated with iron and aluminium components. Methylated arsenic were detected in estuarine sediments.

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