**1.4. Absorption**

Arsenic can be incorporated into the body by ingestion, inhalation or through the skin, more than 90% of the ingested arsenic is absorbed in the gastrointestinal tract. Organic arsenic is easier to excrete and is usually found mainly in meat, seafood, and some cereals. The ability of trivalent arsenic (AsIII) to join groups -SH, confers that toxic capacity while pentavalent arsenic (AsV) interferes with phosphorylation reactions, due to its similarity chemical with phosphate [13]. In food, the organic form is the most frequent and is most susceptible to elimination, except for some types of fish, crustaceans, and algae, in most foods (fruits, vegetables, cereals, meats, etc.) that have arsenic concentration lower than 0.25 mg/kg [13]. After ingestion, arsenic is absorbed in the gastrointestinal tract, then passes into the portal circulation and reaches the liver.

The metabolism of arsenic depends on various reduction and methylation reactions in which enzymes and compounds such as s-adenosylmethionine (SAM), arsenic methyltransferase (AS3MT), glutathione (GSH), and oxidized glutathione (GSSG) participate. Initially, GSH participates in the reduction of AsV to AsIII, which is pH dependent and is influenced by the presence of other substances that can be reduced or oxidized; subsequently, the AS3MT participates in the transfer of a methyl group of the SAM enzyme to the trivalent inorganic arsenic to generate MMA(V) Ácido monometilarsónico (monomethylarsonic acid), this compound is reduced to MMA(III) Ácido metilarsenioso (monomethylarsonous acid) by the action of a specific reductase and in this reaction participate the AS3MT, the GSH, and the GSSH, between other compounds; MMAIII enters a methylation reaction to generate DMA(V) Ácido dimetilarsínico (dimethylarsinic acid), and finally, DMAV can be reduced to DMA(III) Ácido dimetilarsenioso (dimethylarsinous acid). These reactions are carried out regardless of the route of absorption [13, 15].
