Mosaic Fertilizer and one of its subsidiaries have agreed to pay a more than $100,000 fine to federal regulators to settle equipment safety and operational concerns at their western St. James Parish complex for a second time in a little more than two years.
U.S. Environmental Protection Agency inspectors accused Mosaic and the subsidiary, Tampa Port Services, of the maintenance and operational breakdowns following an accidental release of anhydrous ammonia last October, according to a new agreement.
Four contract workers were exposed to the liquid ammonia vapors at Tampa Port inside Mosaic’s Faustina plant along the Mississippi River in the late morning hours of Oct. 27, 2025, according to a state incident report. Two needed oxygen before they were cleared to return to work the same day.
Anhydrous ammonia can be a colorless, toxic gas or a liquid vapor that can cause severe respiratory problems, skin burns, blindness and even death at high enough concentrations, according to the EPA.
The ammonia release occurred as Tampa Port was in a maintenance and construction turnaround where a protective flare system was being added. It had been both preceded and followed by other accidental emissions of ammonia in the months before and after, including a far larger one the prior June, state records show.
Following the Oct. 27 incident, which is the subject of a parallel and still pending state investigation, the companies were accused by the EPA of two violations involving “mechanical integrity,” or ensuring equipment is maintained in a way that prevents dangerous failures and chemical releases.
Under the agreement with EPA, Mosaic and Tampa Port didn’t admit or deny the two violations detailed but waived their rights to appeal the settlement. The full fine was $103,449.50.
Mosaic officials said in a statement they’ve “implemented corrective actions and continue to evaluate our processes to help prevent similar occurrences.” Among them are new worker training, a list of critical spare pressure valves and new quality control procedures for valve settings, Tampa Port has told the state.
In January 2024, Mosaic and Tampa Port Services reached a settlement with EPA involving multiple alleged breakdowns in mechanical integrity over several years. They were accused of not following through quickly enough on their internal hazard analyses and other shortfalls, including failing to test high-pressure ammonia piping for corrosion.
The companies agreed then to pay $217,085 in civil fines and spend another $100,000 on projects in St. James Parish, including 11 new ammonia air monitors.
In the latest case, Tampa Port Services told state regulators that a pressure relief valve opened and released 673 pounds of anhydrous ammonia vapor to an emergency flare. That flare was designed to destroy the vapor but was still under construction, so it was released into the air.
Mosaic Fertilizer’s Faustina plant along River Road in western St. James Parish, as seen Tuesday, Feb. 6, 2024.
Workers recognized the problem immediately, the company said, but it took 30 minutes to bring the release fully under control and halt the vapor.
Tampa Port told the state Department of Environmental Quality that the vapors were dispersed by the wind but did not go off-site, though employees and contractors had to shelter in place while the leak was halted.
Preventable release
Tampa Port is authorized to emit ammonia into the air at concentrations aimed at protecting worker and public health, but the high rate of the accidental release — more than eight times what is allowed per hour — violated the terms of its air permit, DEQ inspectors allege.
Tampa Port later acknowledged the release was preventable. The company told DEQ that a relief valve had been installed with pressure settings too low.
Tampa Port ran into similar alleged problems four months before the October release, according to state reporting.
An estimated 4,436 pounds of anhydrous ammonia were released in 15 minutes on June 4, 2025, from a different piece of equipment when another relief valve had pressure settings that were too low — about 4% off the level required.
This shortfall, which Tampa Port acknowledged was preventable, again caused that emergency valve to open too soon, the company told DEQ. The company had to use water deluge systems to control the release while the unit was shut.
In late December, Tampa Port had a relief valve release of anhydrous ammonia that went to the same flare, which was operating then, keeping ammonia releases at permit levels, the company said.
Both the June and October ammonia releases are part of a more comprehensive listing of alleged air quality and safety process violations that DEQ inspectors have accused Tampa Port of having going back to 2022. The state violations are still pending.
At Faustina, Mosaic processes dry agricultural phosphate fertilizers that also are used as fire retardants. Tampa Port runs an adjacent facility at Faustina that makes anhydrous ammonia, another fertilizer component that supplies critical nitrogen.
The combined complex is just downriver from Donaldsonville and operates in conjunction with Mosaic’s Uncle Sam plant, which is across the river from the St. James complex.
