ANNAPOLIS, Md. (AP) — The state Senate is set to cast a final vote on a bill to ban a chicken feed additive containing arsenic.

The chamber is scheduled to vote Thursday on the measure, which would ban the sale of roxarsone, a chemical used to help the birds grow and fight parasites.

Opponents of the legislation say the bill threatens Maryland’s eastern shore chicken industry and is not necessary because Pfizer Inc. has voluntarily suspended the sale of the chemical.

Perdue Farms, the country’s third-largest chicken company, stopped using it in 2007.

Sponsors of the legislation say the arsenic additive contaminates chicken meat and waste, polluting soil and the Chesapeake Bay.

The legislation has been amended to terminate the ban should the U.S. Food and Drug Administration determine the chemical is safe.