Which form of arsenic is commonly used as a feed additive?

• A. Pentavalent arsenic used as a feed additive.
• B. Inorganic arsenic trioxide used as a herbicide.
• C. Organic arsenic used in heartworm therapy.
• D. Elemental arsenic in ore form.

Answer: (A)

Arsenic in feeds has historically been used in the form of organic compounds where arsenic is in the +5 oxidation state, i.e., pentavalent arsenic. These organoarsenical additives were included in poultry and swine feeds to promote growth and regulate parasites. That specific chemical form—organic arsenic molecules with arsenic in the +5 state used as a feed additive—best fits the idea of a permitted or historically used feed additive, which is why it’s the correct choice.

Inorganic arsenic trioxide is known mainly as a weed killer and pesticide, not a feed additive. An organic arsenic drug used for heartworm therapy is a treatment rather than a feed additive. Elemental arsenic in ore form is not used for animal feeds.