Gel-filtration profile of the arsenic compounds in water extracts of seaweeds

Brown algae contain arsenic higher (22.7-138.3ppm) than other seaweeds and marine foods. The arsenic compound(s) in brown algae can be easily extracted with redistilled water (approximately 40-60% of the initial content). The chemical form(s) of the arsenic compound(s) in several brown algae, Awabi (Haliotis gigantea) and in human urine after eating Hijiki (Hizikia fusiforme) were studied by gel-filtration chromatography (Sephadex G-15). Arsenic in the fractions were determined by flame-less atomic absorption spectrometry. All of the arsenic compound(s) in the water extract of seaweeds eluted earlier than As2O3 (AsO33-), As2O5 (AsO43-) and phenylarsonic acid. The elution volumes (Ve) of the arsenic compound(s) in Makonbu (Laminaria japonica) and Wakame (Undaria pinnatifida) water extracts were identical (Ve=170ml), but different from that in Hijiki (Ve=200ml). The elution profile of arsenic compounds in Matsumo (Heterochrodaria abietina) water extract had two peaks; the early one had approximately the same Ve as those of Makonbu and Wakame (Ve=165ml), while the latter eluted earlier than Hijiki arsenic (Ve=190ml). The elution volume of the arsenic compound(s) in Awabi water extract and in the urine after Hijiki intake, however, was the same as that of Hijiki. On the other hand, an organo arsenic compound in cod liver hydrolysate was isolated by Lunde. According to his report, the UV spectrum of the organo arsenic compound showed a distinct peak at 260nm and the compound contained at least one amino group which is positive in the ninhydrin reaction. However, we found no absorption at 260nm corresponding to any arsenic elution peak from seaweed. The fractions of Hijiki water extract were examined using the ninhydrin reaction, and slight coloration was seen at the position of arsenic.