Eelco Leemans, Technical Advisor to the Clean Arctic Alliance
Scrubbers, or exhaust gas cleaning systems, are an end-of-pipe equipment compliance mechanism employed to remove harmful pollutants and particulate matter from exhaust emissions. However, in a sleight-of-hand, pollutants are then dumped into the ocean, transferring the problem to the marine environment, allowing vessels to continue burning fuels like HSFOs.
There are no global restrictions on scrubbers discharges even in protected areas, but with many countries prohibiting discharges from scrubbers or scrubber use, the International Maritime Organization (IMO) should enact a ban on scrubbers to protect the oceans from large-scale, deliberate pollution. The IMO’s Marine Environment Protection Committee, forthcoming MEPC 83 provides a chance for the shipping industry to escape the false choice of scrubbers.
Scrubbers are designed to clean exhaust emissions from the burning of high sulphur HFOs, removing the sulphur oxides (SOx), by creating a ‘mist’ of seawater in the ship’s smokestack, thereby binding the SOx. In most scrubbers, of the ‘open loop’ type, this seawater is then flushed overboard in massive quantities – over 10 gigatons globally each year – into the ocean, including the Arctic. As this wastewater has a lower pH value than seawater, it contributes to acidification of the ocean, already under severe stress from excess CO2 uptake. As well as SOx, scrubber washwater removes heavy metals, nitrites and nitrates, and polycyclic aromatic hydrocarbons (PAHs) which are highly carcinogenic – and dumps them in the ocean. See “Marine environment at risk due to ship emissions.”
Scrubbers not only lead to toxic discharges in the aquatic environment but also increased air pollution, a new study by Canada states: “… while ships using scrubbers and HFO meet the low-sulphur requirements, they are expected to result in higher amounts of CO2, PM, and Black Carbon compared to using compliant low-sulphur fuels, in particular MGO (marine gas oil)”.
The IMO also must regulate black carbon, a short-lived super pollutant, and shipping’s second largest cause of global warming after CO2, providing around one-fifth of international shipping’s climate impact. With the Arctic warming four times faster than elsewhere, ending scrubber use will help.
In 2020, the International Council for the Exploration of the Sea, which has consultative status at the IMO, published a background report, demonstrating that scrubbers form an additional pressure on the marine environment and that substances found in discharge water ‘can cause acute effects on marine biota and may have further impacts, through bioaccumulation, acidification, and eutrophication, on the structure and functioning of marine ecosystems’.
Scrubber discharges are also toxic to marine wildlife at very low concentrations, increase the rate of death of planktonic animals essential to marine food webs, and cause significant malformations of seabed animals. This has an impact on coastal and Indigenous communities who rely on marine wildlife for food security and cultural continuity.
The International Council for Clean Transportation (ICCT) reports that scrubbers are not equivalently effective at reducing total air pollution emissions compared to using MGO, and that CO2 emissions are 4% higher using HFO with a scrubber compared to distillate fuel or MGO.
In January, 2025 environmental NGOs wrote to the OSPAR Commission (Convention for the Protection of the Marine Environment of the North-East Atlantic) calling for a scrubber discharge ban throughout the territorial waters of the 15 North-East Atlantic States responsible for protecting the marine environment of the North-East Atlantic, which includes Arctic waters. A proposal will be considered at a meeting of OSPAR’s Environmental Impacts of Human Activities Committee in April, with the potential that the proposal be sent to the 2025 OSPAR Ministerial Meeting in June for adoption.
During MEPC 83, member states must back a resolution calling on the shipping sector to not use scrubbers in protected areas, habitats important for endangered wildlife, and other ecologically sensitive areas such as the Arctic. This would provide an interim measure, and a catalyst to focus member states on PPR 13 in early 2026, where mandatory regulation of scrubbers must be agreed.
As the continued use of fossil fuels is being phased out globally, the shipping industry should stop prevaricating and procrastinating, and instead ban the use of scrubbers.
First published on Tradewinds: Viewpoint: Why the IMO should ban the ‘false choice’ of scrubbers
