LA PORTE, Texas (AP) — Four workers received medical treatment and a fifth employee remained missing after a chemical leak Saturday at a suburban Houston industrial plant.

The chemical, methyl mercaptan, began leaking around 4 a.m. Saturday in a unit at the DuPont plant in La Porte, an industrial suburb 22 miles east of Houston. The release was contained by 6 a.m.

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The chemical, which is hazardous, is used to create crop protection products such as insecticides and fungicides.

DuPont spokesman Aaron Woods said four workers had direct exposure to the chemical release. Three of these workers were being evaluated at the facility.

“The three remain at the unit and we’re waiting on the emergency response and medical team to provide us the condition of those three individuals,” Woods said.

The fourth worker was taken to an area hospital. That worker’s condition was not immediately known.

Officials are trying to locate a fifth worker who went missing, Woods said.

Jeff Suggs, emergency management coordinator for La Porte, said the chemical release is not toxic for those living nearby, but that it caused a smell that’s similar to rotten eggs.

“It’s a nuisance smell in the area. It’s a smell that’s traveled quite far,” Suggs said.

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Methyl mercaptan is also commonly used to odorize natural gas — which has no odor — for safety purposes.

The cause of the chemical release was not immediately known. An investigation will begin once the site has been given an all clear, Woods said.

The La Porte plant has 320 DuPont employees. Four other companies are also tenants at the complex.

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