The Missouri Department of Natural Resources is monitoring five manufacturers in Joplin for odor levels after receiving continuing complaints from residents.
Joplin's interim city manager, Dan Pekarek, said the city also reports odor levels to the state agency, but the DNR cannot file a complaint based on a city report.
Ryan Talken, assistant director of the Joplin Health Department, said the city relayed nine complaints in February and two in March to the state.
The Joplin Globe reports two manufacturers — Protein Solutions and Heartland Pet Food — were flagged last week for violations.
The state agency also periodically checks Jasper Products, Hampshire Pet Products and Ajinomoto Foods.
The city's health department says plants that have been investigated in the past have made several upgrades to stop or reduce odors.