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The hydrogen peroxide (H2O2)-generating effects of 14 flavonoids were investigated. Seven out of 14 flavonoids tested were found to generate H2O2 in an acetate buffer of pH 7.4. The H2O2-generating abilities of flavonoids decrease in the order of myricetin > baicalein > quercetin > (-)-epicatechin > (+)-catechin > fisetin = 7,8-dihydroxy flavone. This ability was observed in flavonoids with either a pyrogallol or catechol structure, and the pyrogallol-type flavonoids generated more H2O2 than the catechol-types. The amount of H2O2 generated by myricetin (pyrogallol-type flavonoid) was proportional to its concentration and to the reaction time until about 4 h. In addition, H2O2 generation by myricetin was dependent on the amount of dissolved oxygen in the buffer, and it was inhibited by the addition of superoxide dismutase. These results suggest that the flavonoids generate H2O2 by donating a hydrogen from their pyrogallol or catechol structure to oxygen, through a superoxide anion radical. It was also found that flavonoids which generated more H2O2 were more powerful antioxidants in the NADPH-dependent lipid peroxidation of rat microsomes.

The acute toxicity of methylarsonic acid, CH3AsO(OH)2 (MAA), dimethylarsininc acid, (CH3)2AsO(OH) (DMAA), and trimethylarsine oxide, (CH3)3As0 (TMAO), were examined in mice with oral administration.The LDS0 values of MAA, DMAA and TMAO were 1.8, 1.2 and 10.6 g kg-' respectively. The toxicity of MAA and DMAA was very much lower than that for inorganic arsenic compounds. It was shown that TMAO has a similar acute toxicity to arsenobetaine. On the other hand, when the mice were administered 14.4 g kg-' of TMAO once only orally, a garlic-like odor (trimethylarsine, (CH3)3A~) was definitely detectable in the exhalation of the animals by the human olfactory sense within about a few minutes.

A method for the separation and identification of inorganic and methylated arsenic compounds in marine organisms was constructed by using a hydride generation/cold trap/gas chromatography mass spectrometry (HG/CT/GC MS) measurement system.The chemical form of arsenic compounds in marine organisms was examined by the HG/CT/GC MS system after alkaline digestion. It was observed that trimethylarsenic compounds were distributed mainly in the water-soluble fraction of muscle of carnivorous gastropods, crustaceans and fish. Also, dimethylated arsenic compounds were distributed in the water-soluble fraction of Phaeophyceae. It is thought that most of the trimethylated arsenic is likely to be arsenobetaine since this compound released trimethylarsine by alkaline digestion and subsequent reduction with sodium borohydride.The major arsenic compound isolated from the water-soluble fraction in the muscle and liver of sharks was identified as arsenobetaine from IR, FABMS data, NMR spectra and TLC behaviour.The acute toxicity of arsenobetaine was studied in male mice. The LD, value was higher than 10gkg-'. This compound was found in urine in the non-metabolized form. No particular toxic symptoms were observed following administration. These results suggest that arsenobetaine has low toxicity and is not metabolized in mice. The LD5,, values of other minor arsenicals in marine organisms, trimethylarsine oxide, arsenocholine and tetramethylarsonium salt, were also examined in mice.

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