Arsenic metabolites in humans after ingestion of wakame seaweed

¹ Division of Clinical Laboratory Science, Department of Medical Risk Management, Faculty of Risk and Crisis Management, Chiba Institute of Science, Chiba, Japan
² Research Unit of Environmental Toxicology and Carcinogenesis, School of Pharmacy, Nihon University, Chiba, Japan
³ Department of Preventive Medicine and Environmental Health, Graduate School of Medicine, Osaka City University, Osaka, Japan
⁴ Department of Hygiene and Preventive Medicine, School of Medicine, Showa University, Tokyo, Japan
⁵ Research Center for Occupational Poisoning, Kansai Rosai Hospital, Japan Labour Health and Welfare Organization, Hyogo, Japan

^a ahata@cis.ac.jp
^b nfujitani@cis.ac.jp
^c yamanaka.kenzo@nihon-u.ac.jp
^d endog@med.osaka-cu.ac.jp
^e yamano@med.showa-u.ac.jp
^f haba@med.showa-u.ac.jp
^g yokoendo@kanrou.net

Abstract

Seaweed contains large amounts of various arsenic compounds such as arsenosugars (AsSugs), but their relative toxicities have not yet been fully evaluated. A risk evaluation of dietary arsenic would be necessary. After developing an arsenic speciation analysis of wakame seaweed (Undaria pinnatifida), we conducted a wakame ingestion experiment using volunteers. Five volunteers ingested 300 g of commercial wakame after refraining from seafood for 5 days. Arsenic metabolites in the urine were monitored over a 5-day period after ingestion. Total arsenic concentration of the wakame seaweed was 34.3 ± 2.1 mg arsenic/kg (dry weight, n = 3). Two AsSugs, 3-[5′-deoxy-5′-(dimethyl-arsinoyl)-β-ribofuranosyloxy]-propylene glycol (AsSug328) and 3-[5′-deoxy-5′-(dimethyl-arsinoyl)-β- ribofuranosyl-oxy]-2-hydroxypropyl-2,3-dihydroxy-propyl phosphate (AsSug482) were detected, but arsenobetaine, dimethylarsinic acid (DMA), monomethylarsonic acid, and inorganic arsenics (iAs) were not detected. The major peak was AsSug328, which comprised 89% of the total arsenic. Approximately 30% of the total arsenic ingested was excreted in the urine during the 5-day observation. Five arsenic compounds were detected in the urine after ingestion, the major one being DMA, which comprised 58.1 ± 5.0% of the total urinary arsenic excreted over the 5 days. DMA was believed to be metabolized not from iAs but from AsSugs, and its biological half-time was approximately 13 h.