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Drivers utilize all four lanes of the Sunshine Bridge at dusk, seen from St. James Parish in Louisiana on the east side of the Mississippi River, Thursday, October 31, 2019.

An ammonia leak from the Mosaic Faustina plant in northwestern St. James Parish briefly forced the closure of a stretch of River Road south of the Sunshine Bridge before crews got the release in hand Tuesday afternoon.

Sheriff Willy Martin said crews were able to isolate a leaking line and neutralize the ammonia gas release from the plant along the Mississippi River, allowing officials to give the all-clear around 4 p.m.

"There was no offsite impact as far as affecting anyone," Martin said.

Ammonia is a poisonous but colorless gas with a sharp irritating odor. It can cause serious eye damage and skin burns and is harmful if inhaled.

An accidental release of the gas can pose a serious fire or explosion risk, according to various industrial and government safety data sheets.

Deputies reported the leak and road closure in a communitywide notification about 3:25 p.m. but said the River Road, or La. 18, had reopened by 4:09 p.m.

Martin said the highway was closed as a precaution because of the leak and the wind direction at the time. The Sunshine Bridge remained open during the closure of River Road, however. 

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Though the Faustina plant is immediately surrounded by fields and other chemical facilities, the complex is just south of the busy La. 70 corridor, where gas stations, motels, other businesses and the Ascension Parish jail are located.

Martin said the leak never threatened the La. 70 area.

Greg Langley, spokesman for the state Department of Environmental Quality, said crews inside the plant used water to knock the gas to the ground until the leaking line could be shut.

Morgan Odum, a Mosaic spokeswoman, said the release led to no injuries at the plant. With the leak secured, company officials will investigate the cause.

Mosaic has twin operations in St. James Parish aimed at the agricultural fertilizer market.

A phosphoric acid plant known as Uncle Sam is on the east bank of the Mississippi, while the Faustina plant is on the west bank, north of the St. James community and south Donaldsonville in Ascension Parish.

The Faustina plant makes granular ammonium phosphate fertilizer by reacting ammonia and phosphoric acid. The resulting product is moved by ship, barge, trucks and rail.

Email David J. Mitchell at