TOXICITIES OF 4 ARSENIC SPECIES TO SCENEDESMUS-OBLIGUUS AND INFLUENCE OF PHOSPHATE ON INORGANIC ARSENIC TOXICITIES

Acute toxicities of four arsenic species to freshwater green alga Scenedesmus obliguus in AGP culture medium are determined by counting of cells. The values of 96h-EC(50) are 78.7 mu g, As/L for arsenite; 159.3 mu g, As/L arsenate; 12.4 mg, As/L, monomethylarsenate; 35.7 mg, As/L dimethylarsenate. The relationship between phosphate concentration and the cell log-phase growth rate follows Michaelis-Menten kinetics. When phosphate concentration in the medium is raised, arsenate toxicity to the alga increases, and arsenite toxicity increases first and then decreases.