Arsenic in the human food chain, biotransformation and toxicology – Review focusing on seafood arsenic

• Seafoods contain a variety of mostly organic arsenicals and less inorganic arsenic.
• Major arsenical in fin fish is arsenobetaine and in mussels a variety of arsenosugars.
• Human metabolism of seafood arsenicals vary greatly, some occur in the intestine.
• Arsenobetaine, dimethyl and monomethyl arsonate are formed in humans.
• Pathways and possible formation of trivalent toxic intermediates are unknown.

Fish and seafood are main contributors of arsenic (As) in the diet. The dominating arsenical is the organoarsenical arsenobetaine (AB), found particularly in finfish. Algae, blue mussels and other filter feeders contain less AB, but more arsenosugars and relatively more inorganic arsenic (iAs), whereas fatty fish contain more arsenolipids. Other compounds present in smaller amounts in seafood include trimethylarsine oxide (TMAO), trimethylarsoniopropionate (TMAP), dimethylarsenate (DMA), methylarsenate (MA) and sulfur-containing arsenicals. The toxic and carcinogenic arsenical iAs is biotransformed in humans and excreted in urine as the carcinogens dimethylarsinate (DMA) and methylarsonate (MA), producing reactive intermediates in the process. Less is known about the biotransformation of organoarsenicals, but new insight indicates that bioconversion of arsenosugars and arsenolipids in seafood results in urinary excretion of DMA, possibly also producing reactive trivalent arsenic intermediates. Recent findings also indicate that the pre-systematic metabolism by colon microbiota play an important role for human metabolism of arsenicals. Processing of seafood may also result in transformation of arsenicals.