Improving the Efficiency of Organoarsenic Extraction from Seaweeds

Abstract

Seaweeds are a source of arsenosugars (AsSug). AsSug are mainly metabolized to dimethylarsenic species, but their relative health risks have not yet been fully evaluated. Therefore, it is essential to assess the risk of AsSug intake. Although AsSug are water-soluble arsenics, the extraction efficiency of arsenic compounds from wakame seaweed specimens (Undaria pinnatifida) ranges only between 4 and 49%. To develop a high recovery-rate extraction method without altering the chemical structure of the arsenic compounds, we examined the efficacy of a combined enzymatic treatment and methanol (MeOH) extraction method. After treatment with cellulase and alginate lyase and extraction with 100% MeOH, we extracted 88.8% of the arsenic compounds in wakame without arsenic species alteration. Four arsenic peaks were detected using high performance liquid chromatography with inductively coupled plasma mass spectrometry (HPLC-ICP-MS), two of which were identified as 3-[5′-deoxy-5′-(dimethylarsinoyl)-β-ribofuranosyloxy]-2-hydroxypropylene glycol and 3-[5′-deoxy-5′-(dimethylarsinoyl)-β-ribofuranosyloxy]-2-hydroxypropyl-2,3-hydroxypropyl phosphate by using HPLC-electrospray ionization-quadrupole–time-of-flight mass spectrometry (HPLC-ESI-Q-TOF-MS). Further, the HPLC-ESI-Q-TOF-MS analyses suggested that, of the remaining two peaks, one corresponded to arsenic-hydrocarbon 388 (C₂₁H₄₅OAs) and arsenic-phospholipid 1012 (C₄₉H₉₄O₁₄PAs). Thus, our method can be used to extract arsenic compounds from brown algae with strong cell walls.