Clinical Information

Arsenic (As) exists in a number of different forms; some are toxic, while others are not. The toxic inorganic forms are arsenite (As[3+], As[III]) and arsenate (As[5+], As[V]), and their partially detoxified metabolites are monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA). As(III) is more toxic than As(V), and both are more toxic than MMA and DMA. The biologic half-life of inorganic arsenic is 4 to 6 hours, while the biologic half-life of the methylated metabolites is 20 to 30 hours. Target organs of As(III)-induced effects are the heart, gastrointestinal tract, skin and other epithelial tissues, kidney, and nervous system.

Inorganic arsenic is carcinogenic to humans. Symptoms of chronic poisoning, called arseniasis, are mostly insidious and nonspecific. The gastrointestinal tract, skin, and central nervous system are usually involved. Nausea, epigastric pain, colic abdominal pain, diarrhea, and paresthesias of the hands and feet can occur.

Nontoxic, organic forms of arsenic are present in many foods. Arsenobetaine and arsenocholine are the 2 most common forms of organic arsenic found in food. The most common foods that contain significant concentrations of organic arsenic are shellfish and other predators in the seafood chain (cod, haddock, etc). Some meats, such as meats from chickens that have been fed seafood remnants, may also contain the organic forms of arsenic.

Following ingestion of arsenobetaine and arsenocholine, these compounds undergo rapid kidney clearance to become concentrated in the urine. Organic arsenic is completely excreted within 1 to 2 days after ingestion, and there are no residual toxic metabolites. The biologic half-life of organic arsenic is 4 to 6 hours.

For reporting purposes, the concentrations of the inorganic forms (As[III] and As[V]) along with the methylated forms (MMA and DMA) will be summed and reported together as 'inorganic' arsenic. This is consistent with how the biological exposure index reference range is reported.