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To reduce the arsenic content of the leaves and branches of an edible brown alga, hijiki Hizikia fusiforme, the Japanese traditional washing and soaking process before cooking was shown to be effective: about 32 to 60% of the arsenic was removed from the alga at room temperature. Increasing the amount of water in which the hijiki was soaked did not affect arsenic removal. On the other hand, arsenic content decreased linearly as the temperature used to wash and soak hijiki increased from 0 to 60°C. In the washed and soaked hijiki, inorganic arsenic accounts for 90% of the total arsenic and dimethylated arsenic compounds 10%. Copyright #

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Tolerance, bioaccumulation, biotransformation and excretion of arsenic compounds by the freshwater shrimp (Neocaridina denticulata) and the killifish (Oryzius latipes) (collected from the natural environment) were investigated. Tolerances (LC,,) of the shrimp against disodium arsenate [abbreviated as As(V)], methylarsonic acid (MAA), dimethylarsinic acid (DMAA), and arsenobetaine (AB) were 1.5, 10, 40, and 15Opg As ml-I, respectively. N . denticulata accumulated arsenic from an aqueous phase containing 1 pg As ml-' of As(V), 10 pg As ml-' of MAA, 30 pg As ml-' of DMAA or 150 pg As ml-' of AB, and biotransformed and excreted part of these species. Both methylation and demethylation of the arsenicals were observed in oiuo. When living N. denticulata accumulating arsenic was transferred into an arsenic-free medium, a part of the accumulated arsenic was excreted. The concentration of methylated arsenicals relative to total arsenic was higher in the excrement than in the organism.Total arsenic accumulation in each species via food in the food chain Green algae (Chlorella oulgaris) +shrimp (N.denticulatu) -+killifish (0. lafipes) decreased by one order of magnitude or more, and the concentration of methylated arsenic relative to total arsenic accumulated increased successively with elevation in the trophic level. Only trace amounts of monomethylarsenic species were detected in the shrimp and fish tested. Dimethylarsenic species in alga and shrimp, and trimethylarsenic species in killifish, were the predominant methylated arsenic species, respectively.

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A certified reference material, NMIJ CRM 7405-a, for the determination of trace elements and As(V) in algae was developed from the edible marine hijiki (Hizikia fusiforme) and certified by the National Metrology Institute of Japan (NMIJ), the National Institute of Advanced Industrial Science and Technology (AIST). Hijiki was collected from the Pacific coast in the Kanto area of Japan, and was washed, dried, powdered, and homogenized. The hijiki powder was placed in 400 bottles (ca. 20 g each). The concentrations of 18 trace elements and As(V) were determined by two to four independent analytical techniques, including (ID)ICP-(HR)MS, ICP-OES, GFAAS, and HPLC-ICP-MS using calibration solutions prepared from the elemental standard solution of Japan calibration service system (JCSS) and the NMIJ CRM As(V) solution, and whose concentrations are certified and SI traceable. The uncertainties of all the measurements and preparation procedures were evaluated. The values of 18 trace elements and As(V) in the CRM were certified with uncertainty (k = 2).

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