Maryland became the first state to ban the use of additives containing arsenic in chicken feed Tuesday. The measure is among several new statewide laws that took effect Jan. 1.
State lawmakers passed a bill banning the chemical last year. It's used to help poultry and other fowl grow and fight parasites.
Pfizer Inc., which distributes the product, stopped selling the additive in July 2012 after a U.S. Food and Drug Administration study found higher levels of inorganic arsenic in chickens treated with the chemical. Arsenic is a known carcinogen.
Opponents of the Maryland law said the measure wasn't needed because the company voluntarily suspended sales of the product.