In arsenic toxicokinetics, which statement is true?

• A. Absorption occurs only via inhalation.
• B. Metabolism primarily involves methylation of inorganic arsenic.
• C. Excretion is slow over months.
• D. Pentavalent arsenic is excreted primarily in bile.

Answer: (B)

Inorganic arsenic is mainly handled by the liver through methylation, converting it to mono- and dimethylated forms (MMA and DMA). This methylation is the primary metabolic step and serves to make arsenic more water-soluble, promoting its excretion in urine. While some methylated intermediates can have toxicity of their own, the overall effect is enhanced clearance from the body, which is why this pathway is highlighted as the key metabolic process in arsenic toxicokinetics.

Absorption is not limited to inhalation; arsenic is also readily absorbed from the gastrointestinal tract, so limiting entry to the lungs isn’t accurate. Excretion is not slow for months; the bulk of arsenic is cleared in the urine within a short time frame. And the main route of excretion is renal, with bile playing only a minor role.