Graphite furnace and hydride generation atomic absorption, GFAA and HGAA, techniques have been developed and applied to the determination of arsenic concentrations in some marine invertebrates, mainly bivalves and gastropods, of British Columbia. Total arsenic concentrations in bivalves vary with species, ranging from 0.6-9.1 μg g⁻¹ (wet weight basis). Arsenic concentrations in the bivalve shells show a wider range of 0.1 to 26.3 μg g⁻¹ (dry weight basis). Gastropods show relatively higher arsenic concentrations in the soft tissues, 17.3-48.4 fig μg g⁻¹, and concentrations in the shells range from 1.4 to 16.3 fig μg g⁻¹. There is no correlation between arsenic levels in the soft-tissues and shells. There is also no correlation between arsenic levels in the organisms and the surrounding sediments and sediment pore waters. HPLC-GFAA techniques have been developed and used for the separation and quantitation of-arsenite, arsenate, methylarsonic acid, dimethylar-sinic acid, arsenobetaine, arsenocholine iodide and tetramethylarsonium iodide. This technique together with TLC, NMR, FAB and thermospray LCMS were employed for the detection of water-soluble arsenic compounds in 5 species of clams - Butter clam Saxidomus giganteus. Horse clam Schizothoerus nuttalli. Soft-shelled clam Mva arenaria. Native-littleneck clam Protothaca staminea and Manila clam Venerupis laponica. Varying amounts of arsenobetaine and tetramethylarsonium ion are found in all the clams. Butter clams show the pres ence of a third compound which appears to be trimethylarsine oxide. Small amounts of unknown arsenic containing compounds are present which are yet to be characterized . Arsenic speciation in 3 gastropods was also examined. The Northwest neptune Neptunea lvrata. the Thick-ribbed whelk Berinpius crebriscotata and Phoenician whelk Neptunea phoenicius all contain arsenobetaine and at least two unidentified arsenicals. / Science, Faculty of / Chemistry, Department of / Graduate