BIOMETHYLATION AND BIOTRANSFORMATION OF ARSENIC IN A FRESH-WATER FOOD-CHAIN - GREEN-ALGA (CHLORELLA-VULGARIS)-]SHRIMP (NEOCARIDINA-DENTICULATA)-]KILLIFISH (ORYZIAS-LATIPES)

Tolerance, bioaccumulation, biotransformation and excretion of arsenic compounds by the freshwater shrimp (Neocaridina denticulata) and the killifish (Oryzias latipes) (collected from the natural environment) w ere investigated. Tolerances (LC50) of the shrimp against disodium ars enate [abbreviated as As(V)], methylarsonic acid (MAA), dimethylarsini c acid (DMAA), and arsenobetaine (AB) were 1.5, 10, 40, and 150 mug As ml-1, respectively. N. denticulata accumulated arsenic from an aqueou s phase containing 1 mug As ml-1 of As(V), 10 mug As ml-1 of MAA, 30 m ug As ml-1 of DMAA or 150 mug As ml-1 of AB, and biotransformed and ex creted part of these species. Both methylation and demethylation of th e arsenicals were observed in vivo. When living N. denticulata accumul ating arsenic was transferred into an arsenic-free medium, a part of t he accumulated arsenic was excreted. The concentration of methylated a rsenicals relative to total arsenic was higher in the excrement than i n the organism. Total arsenic accumulation in each species via food in the food chain Green algae (Chlorella vulgaris) --> shrimp (N.denticu lata) --> killifish (0. latipes) decreased by one order of magnitude o r more, and the concentration of methylated arsenic relative to total arsenic accumulated increased successively with elevation in the troph ic level. Only trace amounts of monomethylarsenic species were detecte d in the shrimp and fish tested. Dimethylarsenic species in alga and s hrimp, and trimethylarsenic species in killifish, were the pre-dominan t methylated arsenic species, respectively. freshwater food chain, gre en alga, shrimp, killifish.