BIOMETHYLATION OF ARSENIC IN AN ARSENIC-RICH FRESH-WATER ENVIRONMENT

Arsenic circulation in an arsenic-rich freshwater ecosystem was elucid ated to detect arsenic species in the river water and in biological sa mples living in the freshwater environment, Water-soluble arsenic comp ounds in biological samples were extracted with 70% methanol, Samples containing arsenic compounds in the extracts were treated with 2 mol d m(-3) of sodium hydroxide and reduced,vith sodium borohydride, The det ection of arsenic species was accomplished using a hydride generation/ cold trap/cryofocus/gas chromatography-mass spectrometry (HG/CT/CF/GC- MS) system, The major arsenic species in the river water, freshwater a lgae and fish are inorganic arsenic, dimethylarsenic and trimethylarse nic compounds, respectively. Trimethylarsenic compounds are also detec ted in aquatic macro-invertebrates, The freshwater unicellular alga Ch lorella vulgaris, in a growth medium containing arsenate, accumulated arsenic and converted it to a dimethylarsenic compound, The water flea Daphnia magna, which was fed on arsenic-containing algae, converted i t to a trimethylarsenic species. (C) 1997 by John Wiley & Sons, Ltd.