The objective of this project is the isolation and identification of chemical species containing arsenic which are formed by the algae Tetraselmis chuii and Daphnia magna. Both organisms produce arsenic compounds, when grown in a medium containing inorganic arsenate at the ppm level, which migrate with the lipids upon extraction of the organisms with CHCl3/CH3OH. T. chuii has been cultivated in 1000 liter tanks. A high pressure liquid chromatographic method has been developed for the separation of the arsenic compounds from the lipids. The goal for the third year of this project is the isolation of weighable quantities of the arsenic compound(s), their characterization, and the determination of the identity of the arsenic compounds remaining in the extraction residue. Work with Daphnia will be directed toward obtaining large quantities of arsenic-containing Daphnia lipids. The ultimate goal of this work is the determination of the manner in which arsenic becomes incorporated into various organisms, to learn about the true toxicity of arsenic compounds and whether arsenic may, in fact, be an essential trace element.