The Dirty Secret of Shipping: How ‘Scrubbers’ Clean the Air – While Contaminating the Sea | Shipping emissions


In 2019, Alan Ladd, a marine engineer, was on a slowing cruise ship to give passengers a better view of the Hubbard Glacier – the largest tidal glacier in North America. Looking briefly away from the harbor seals and killer whales, Ladd noticed a jet of black grease, with a rainbow sheen, bubbling on the surface of the water.

“The only reason I saw it was because the ship had stopped. All of a sudden I could see this pollutant and soot,” says Ladd, who works with the Alaska’s Ocean Ranger Program as one of many independent observers of shipping effluents. “What really bothered me more than anything was that they didn’t do anything about it.”

What Ladd saw was the result of a decision by the shipping industry to reduce air pollution at the expense of the ocean.

After the International Maritime Organization (IMO) decided to reduce sulfur emissions into the atmosphere – which regulators say are harmful to human health – the shipping industry has been faced with the choice of switching to a cleaner but more expensive fuel or to install a system to clean the exhaust gases. – known as “scrubbers” – which dump the chemicals removed from the exhaust directly into the sea.

Scrubbers are dirty and very cheap, but in 2020 more than 4,300 ships worldwide had them installed, compared to 732 ships in 2018.

A container ship at Tsing Yi Port, Hong Kong. Approximately 10,000,000,000 tonnes of scrubber washwater enters the oceans each year. Photography: Suriyapong Thongsawang/Getty

It’s a compromise: clean the sky but contaminate the waters.

“The writing has been on the wall for many years with scrubbers and their environmental implications,” says Andrew Dumbrille, adviser for the Clean Arctic Alliancea coalition of environmental organizations working to protect the polar region from the impact of shipping.

“The problem is that more ships are going to install scrubbers, and so the problems are expected to get worse.”

The race to install scrubbers has only recently begun. In January 2020, the IMO – the UN body overseeing maritime transport – announced a new global sulfur cap of 0.5%, down from 3.5%. To achieve this goal, he urged the global maritime fleet to switch to low sulfur fuel.

But it also allowed for “equivalent” compliance measures, as long as ships reduced their emissions.

Scrubbers have proven to be the cheapest way to do this. The cost of buying and installing a scrubber is £1.5-5m, while cleaner fuel is £250-400 a tonne. The purifier pays for itself in one year.

“It has been an escape for the industry to continue burning the cheapest and dirtiest fuels,” says Lucy Gilliam, from Seas at Risk, an association of European environmental organisations.

Scrubbers, which are found in the exhaust funnels or stacks of ships, use seawater to atomize or “scrub” sulfur dioxide pollutants from engine exhaust.

Microscopic image of crustaceans
Ship wash waters in the North Sea have been found to have ‘serious toxic effects’ on zooplankton, the tiny crustaceans that serve as food for cod, herring and other fish. Photography: tonaquatic/Getty/iStockphoto

Most ships use an open-loop system, which means that instead of keeping waste in a tank to be disposed of at dedicated port facilities, ships directly dump the acid wash – up to 100,000 times more acid than seawater – overboard, says Eelco Leemans, an Arctic marine researcher.

According to a International Clean Transportation Council (ICCT) on the waste discharged worldwide – slightly less than the total weight of all cargo carried by ships in a year.

Toxins don’t just disappear. In addition to being acidic, scrubbers contain heavy metals that accumulate in marine food chains. The Swedish Environmental Research Institute found that North Sea ship wash water has ‘serious toxic effects’ on zooplankton, on which cod, herring and other species feed. Meanwhile, a Belgian study found that discharges from the scrubber contain high concentrations of metals such as nickel, copper and chromiumthat devastate all marine ecosystems.

Of most concern to experts, however, are polycyclic aromatic hydrocarbons (PAHs). These have been linked to several types of cancers and reproductive dysfunction in marine mammals, including the southern resident killer whale in the North Pacific and beluga whales.

“A lot of the release is toxic and contains all these harmful substances,” says Leemans, adding, “It’s the whole cocktail that makes it even worse.”

An IMO spokeswoman, Natasha Brown, said the scrubbers were developed as an “equivalent” to comply with air pollution limits and the IMO is now looking into the wider issue in response to concerns.

Approximately 80% of scrubber discharges occur within 200 nautical miles of shorewith global hotspots along major shipping routes including the Baltic Sea, North Sea, Strait of Malacca and Caribbean Sea, according to the ICCT.

The United States has the highest amounts of scrubber washwater discharges, followed by the United Kingdom, mainly due to its 14 overseas territories, particularly the Cayman Islands.

Cruise ships, like the one Ladd was on, were early adopters of scrubbers. They count for 15% of discharges from scrubbers in ports, even though they represent only 4% of ships equipped with scrubbers.

Cruise lines that travel up the Canadian Pacific coast to Alaska are particularly prone to water pollution. According to a report by environmental organizations Stand.earth and West Coast Environmental Law.

For Ladd, the solution is simple: stop using scrubbers. A few nations have done so, restricting or banning the use of open loop scrubbers in their waters; One of the most recent restrictions came in March in Vancouver, the world’s fourth most polluted port from scrubber washwater.

In 2021, the IMO updated its guidelines for scrubbers, setting stricter limits for open-loop scrubbers on acidity and releases of polycyclic aromatic hydrocarbons and nitrates. In June this year, the IMO Marine Environment Protection Committee approved additional scrubber guidelines. Ultimately, however, UN member states must enforce any action.

And regardless of the stricter measures, experts agree it was a mistake on the part of regulators to allow scrubbers.

“It’s a huge mistake,” Gilliam said. “We could solve the problem of sulfur pollution by switching to cleaner fuels. But instead, we’re just shifting the problem from place to place. And it’s really frustrating.

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