When exhaust gas scrubbers hit the scene ahead of the imposition of a global cap on shipping’s sulphur emissions, it sparked a debate over the compounds that they would pump into the ocean, even as they prevented harmful pollutants from entering the atmosphere.
That debate has not ended, and it is not likely to end any time soon as scientists learn more about the impacts of what is coming out of these devices.
Some environmentalists want exhaust gas cleaning systems banned altogether, while those in the industry who have invested in scrubbers are resistant to restrictions.
But scrubbers need not be banned to address concerns over discharges, and the industry and regulators should embrace science that tells us more about the impact of shipping on the environment, however inconvenient the results may be.
That is because scrubbers emerged out of evolving pollution regulations by the International Maritime Organization, and those regulations will evolve further. The discharges from exhaust gas cleaning systems should not be immune from that progress.
From sulphur to nitrogen oxides, from garbage to oil, the International Convention for the Prevention of Pollution from Ships (Marpol) has been amended over time to reduce pollution into the atmosphere and into the sea.
Scrubbers are deployed to great profit when bunker prices are right, to let ships keep using fuel oil after the global cap on SOx in 2020 and in emissions control areas in some parts of the world.
Proponents of the devices point to research that showed minimal impact on the environment. The Exhaust Gas Cleaning Systems Association, for example, commissioned Danish consultancy DHI to look at the toxicity of scrubber discharges.
The 2021 ecotoxicity study found no harm to fish. Algae and crustaceans were negatively affected only at high concentrations. Larval development tests on crustaceans showed the highest sensitivity.
But DHI’s overall conclusion was that the discharge from open-loop scrubbers represented an acceptable risk level.
Also in 2021, an independent board of experts convened by the Japanese government came to a similar conclusion, noting that the risk that scrubber discharge water presents to marine organisms is “negligible” from short and long-term perspectives.
But as our Green Seas newsletter reports, scientists in the European Union-funded EMERGE project have found that, in early stages of life, waterborne organisms are sensitive to discharge at even tiny concentrations of discharge water.
The implication may be that the pollutants emitted from scrubbers — and even closed-loop variety discharge bleed-off — have impacts on the environment that were not factored in when the devices were approved as a way to comply with the IMO’s sulphur cap.
For Maria Granberg, a marine ecotoxicologist who has been working on the EMERGE research, what is needed is a halt to such discharges into the ocean.
But that does not necessarily mean scrubbers should be banned; there could be a solution that involves offloading scrubber discharges onshore.
It is not immediately clear whether that solution is technically feasible, given the volumes of water involved. But shipping, technology companies and regulators should engage with the evolving science around the impact of scrubber discharge by exploring solutions.
The need to tackle pollution, and the regulations that come out of that, is where scrubbers came in, after all. It is also where oily water separators and very low sulphur fuel oil came from and where decarbonisation solutions will continue to come from.
What is encouraging about the EMERGE project, which is focused mostly on air emissions, is seeing a major shipping company as a partner. By playing that role, Danaos Shipping sends a message that it is opening its eyes to new research on the impacts of its business.
Scrubbers emit heavy metals, nitrates and polycyclic aromatic hydrocarbons into the ocean. They increase acidity in an environment already suffering from ocean acidification. Even if some experts find the levels to be acceptable, no one can say that these compounds are a good thing for the marine environment (although some argue that low-sulphur fuels have higher carbon content).
After all, the march of global environmental regulation has been towards reducing emissions from shipping into the air as well as the sea.