Environmental Groups Urge IMO: Keep Ammonia Waste Out of the Ocean

A coalition of environmental and clean-shipping groups is urging the International Maritime Organization to block any move that would allow ammonia-fueled ships to discharge toxic waste at sea, warning that shipping’s push toward zero-emission fuels must not come at the expense of ocean health.

The call follows last week’s meeting of the IMO’s Pollution Prevention and Response Sub-Committee in London, where member states debated— for the first time—how to regulate ammonia wastewater. The waste is generated when excess ammonia gas is captured during routine ship operations, typically by dissolving it into water, creating a highly toxic liquid byproduct.

In a joint statement issued today, seven organizations warned that proposals allowing “conditional” discharge based on dilution or operational thresholds risk normalizing pollution before the impacts are fully understood. Their message was blunt: dilution is not a solution.

A New Fuel, a New Risk

Green ammonia is emerging as a leading contender in shipping’s decarbonization toolkit. But while it promises major reductions in greenhouse gas emissions, it introduces a new environmental hazard.

During fuel line purging or maintenance, leftover ammonia must be safely removed. The most common method absorbs the gas into water, producing ammonia-laden effluent that is corrosive, acutely toxic, and potentially harmful even at low concentrations.

Some IMO member states have suggested allowing this waste to be discharged into the ocean under tightly controlled conditions. Environmental groups argue that approach focuses too narrowly on short-term toxicity and ignores cumulative, long-term effects.

They warn that repeated low-level discharges could add significant reactive nitrogen to marine ecosystems, contributing to eutrophication, oxygen depletion, and acidification—pressures many regions already face.

A System Already Under Strain

Several groups pointed to the global nitrogen cycle, which scientists say has already exceeded safe planetary boundaries. Adding a new, routine source of nitrogen pollution from shipping, they argue, would compound an existing problem.

With projections suggesting 35 to 50 percent of the global fleet could eventually run on green ammonia, the scale of the issue could be enormous. What begins as a “conditional” exception could quickly become standard practice across tens of thousands of vessels.

Retain It Onboard—or Don’t Use It

Instead of ocean discharge, the coalition is calling for mandatory onboard retention of ammonia effluent, with offloading at port reception facilities. They argue the waste could potentially be reused by chemical or fertilizer industries, turning a disposal problem into a circular-economy opportunity.

Until long-term ecological impacts are better understood, they say, the precautionary principle should apply: no discharge at sea.

Four Clear Demands

The groups outlined four specific actions they want IMO member states to take:

• Prohibit routine or conditional discharge of ammonia effluent at sea
• Address long-term ecosystem and reactive nitrogen impacts—not just acute toxicity
• Develop a global framework for onboard retention and port offloading, including scaling port reception facilities
• Launch a transparent, science-based work program to close key evidence gaps before ammonia adoption scales up

Their warning is consistent across the board: ammonia must not become shipping’s next pollution problem.

As the industry races to cut carbon, environmental groups say the credibility of the fuel transition itself is on the line. Shifting risk from the atmosphere to the ocean, they argue, could ultimately slow adoption by undermining public trust—just as zero-emission fuels are poised to scale.

For ammonia to succeed, they say, it has to be done right from the start.

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