JACKSON, Miss. (AP) — The Mississippi Commission of Environmental Quality has fined Columbus steel mill Severstal $135,000 because the company’s pollution-control monitors didn’t function properly after the plant expanded in June 2011.

The company agreed to pay the fine May 12. It’s the largest environmental fine assessed by Mississippi since it fined Denbury Resources $662,500 last year over a 2011 oil well blowout in Yazoo County.