Arsenic compounds in the freshwater green microalga Chlorella vulgaris after exposure to arsenite

The freshwater green alga, Chlorella vulgaris, was cultivated in a modified Detmer medium in the presence of arsenite in order to investigate tolerance, accumulation, transformation and excretion of arsenic species. When the alga was exposed to arsenite, arsenic accumulation markedly increased in the beginning of the log phase, rose to a maximum of 610 mu g As g(-1) and then decreased during the period from 40 to 120 h after inoculation. Arsenate was the major metabolite in the algal cell; trimethylarsenical species (TMA) were also found 36 h after inoculation when the alga was exposed to arsenite at levels of 70 - 100 mu g As cm(-3). At arsenite levels of 10 - 20 mu g As cm(-3), cell growth was higher than in an arsenic-free medium. Arsenite accumulated in Chlorella vulgaris was transformed to arsenate through bio-oxidation and to a small degree to methyl-, dimethyl-, and trimethyl-arsenic species through biomethylation, Furthermore, the arsenic metabolites were readily excreted under conditions undesirable for the growth of the alga, Total arsenic accumulation decreased with an increase in arsenite concentration in the medium. Copyright (C) 1999 John Wiley & Sons, Ltd.