The adoption of ship scrubbers—technology meant to clean up dirty fuel—has caused a surge in heavy metal pollution.

Baltic Sea, Ship Scrubbers Have Caused Millions of Dollars Worth of Environmental Damage

Baltic Sea, Ship Scrubbers Have Caused Millions of Dollars Worth of Environmental Damage

The adoption of ship scrubbers—technology meant to clean up dirty fuel—has caused a surge in heavy metal pollution.

by Lina Zeldovich

September 27, 2024

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In early 2020, people in port cities around the world started breathing a little easier thanks to new regulations from the International Maritime Organization (IMO)—the overseer of international shipping—that restricted how much sulfur oxide pollution ships could have in their exhaust. Sulfur oxides, also known as SOX gases, can trigger a rash of ill effects, including heart and lung diseases and asthma. Worldwide, sulfur pollution is linked to some 400,000 premature deaths and 14 million new childhood asthma cases each year.

Shipping companies largely complied with the IMO’s new rule. But one of the prime tools in this cleanup effort—devices known as ship scrubbers—had an unfortunate side effect. While the technology has successfully diverted boatloads of pollutants from the air, it has also sent a steady flow of heavy metals into the sea, contaminating marine life and causing millions of dollars worth of damage.

The problem wasn’t negligence or oversight, according to Erik Nøklebye, the CEO of the Swedish shipping company Wallenius Lines, but rather an example of an “imperfect innovation solution.” When the IMO issued its new regulations, says Nøklebye, shipping companies essentially had two options: switch from the default heavy fuel oil to more expensive low-sulfur fuel, or install a ship scrubber—a device that sprays ocean water onto exhaust gases before they leave the engine, capturing the harmful SOX gases as a sulfuric acid solution.

Ship scrubbers come in two types: closed-loop and open-loop. Closed-loop scrubbers store the resulting sludgy, sulfurous mix in a tank that must be emptied at port. Open-loop scrubbers dump that slurry straight into the sea. Ocean water already contains a lot of sulfurous compounds, so many people weren’t too concerned about adding more. And because open-loop scrubbers save space and weight compared with their closed-loop counterparts, many ship owners have favored them.

Much more insidious compounds lurk within fossil fuel ship exhaust, however, including potent toxicants such as heavy metals and polycyclic aromatic hydrocarbons. And for ships running open-loop scrubbers—or even closed-loop scrubbers that have overtopped their storage tanks—all of this, too, has been going straight into the water. So, over time, ship scrubbers have sent a flow of toxic compounds into coastal waterways worldwide.

“If you only look at sulfur, it doesn’t look too bad,” explains Anna Lunde Hermansson, who studied scrubber pollution as a graduate student at the Chalmers University of Technology in Sweden. “But if you instead then consider the dangerous particles and heavy metals and organic compounds that you also find in the exhaust, then you see the big problem.”

Some environmental organizations did warn of this outcome when scrubbers first became available. And as Hermansson and her colleagues show in new research, between 2014 and 2022 more than 10 billion cubic meters of toxic scrubber water was released into the world’s oceans every year. Focusing on the nearby Baltic Sea, the scientists estimate that extra pollution caused more than US $750-million worth of environmental damage—a figure calculated based on models for people’s willingness to pay to avoid marine environmental degradation.

Other scientists back the findings, showing the detrimental effects of ship scrubber water pollution on ocean life. Research shows that when exposed to scrubber water some creatures, such as pelagic copepods, simply die while others, including certain mussels, struggle to develop.

Of the roughly 60,000 large ships that sail the world’s seas, only 4,379 use scrubbers, says Natasha Brown, the head of public information at the IMO. “That’s a small percentage. It’s certainly not a majority of ships,” she says.

According to Brown, scrubbers were never supposed to be the ultimate solution to ships’ sulfur problem. When the IMO issued its sulfur regulation, Brown says the intent was to spur the shipping industry to come up with innovative solutions—whether they be cleaner fuels or new technologies to clean exhaust to acceptable levels. But many shipping companies went for scrubbers as an easier option. Over time, the IMO has responded by tightening regulations on scrubber water discharge, such as by putting limits on its acidity. “It’s a continuous process,” says Brown, adding that the IMO welcomes any new studies so it can revisit or change the guidelines.

Scrubbers do what they set out to do: reduce sulfur pollution. “But I think we, fairly early on, should have discovered that it was more of a stopgap,” says Nøklebye.

That’s why, in June 2024, several shipping industry executives including Nøklebye collaborated with Hermansson’s team to call on the Swedish government to ban open-loop scrubbers, arguing that the devices cause unacceptable damage to marine ecosystems. Shortly after, the Swedish government announced a move to ban water discharges from open-loop scrubbers in its maritime territory starting in July 2025, and from all scrubbers by January 2029. The Danish government followed suit with the same ban dates. Meanwhile, China, Singapore, and Germany had already banned open-loop scrubbers in their coastal waters shortly after ships started installing them.

“Innovations and new ideas are never perfect,” says Nøklebye. But “the industry finally caught onto the fact that this was not the environmental solution that maybe they had hoped for.”

Edited by Colin Schultz