VIEWPOINT: Time to Pull the Plug on Scrubbers in Shipping

The German Environment Agency has recently concluded that scrubber washwater discharge “poses an unacceptable risk.” File Image / Pixabay

As the shipping industry faces mounting pressure to reduce emissions, one of its most misleading compromises has been the use of exhaust gas cleaning systems—commonly known as scrubbers.

Installed on vessels to remove sulphur oxides from the exhaust of heavy fuel oil (HFO), scrubbers allow ships to continue burning the cheapest and dirtiest fuel available, all while claiming to meet environmental standards.

The Science is Clear

The shipping industry emits vast quantities of air pollutants that threaten human health and the environment. To address this, the International Maritime Organization (IMO) introduced sulphur limits in marine fuels.

Rather than switching to cleaner fuels, many shipowners opted for scrubbers, enabling them to continue burning toxic HFO while "cleaning" the exhaust gases from sulphur oxides, they shift the pollution from the air to the sea.

Scrubber washwater contains a toxic cocktail of heavy metals (nickel, vanadium, copper), polycyclic aromatic hydrocarbons (PAHs), and acidic compounds.

Peer-reviewed research by trusted institutions (e.g. Chalmers paper in Nature Sustainability, Jalkanen et al. 2024, Zapata Restrepo et al. 2024, Genitsaris et al. 2023, Picone et al. 2023), government studies (e.g. Schmolke et al. 2020, EU EMERGE 2021, BSH-ImpEx 2023) — have repeatedly shown that scrubber washwater is toxic to marine life.

ImpEx Project found that many washwater samples caused high to extreme toxicity and even mutagenic effects. Studies found measurable effects on biodiversity, reproduction, and nutrient cycles in the marine food web even at dilutions of just 1.5% (e.g. EU EMERGE project).

Despite claims from the scrubber lobby that washwater quickly disperses, research shows that discharges especially were it amasses like in harbours, estuaries, and busy shipping lanes the toxics accumulate in sediments over time, degrade water quality, and harm sensitive ecosystems.

Some pollutants, like PAHs and heavy metals, persist in the environment and bioaccumulate even in the food chain—eventually ending up on our plates.

Studies show both acute and chronic toxicity, including mutagenicity. Multiple studies show significant effects on zooplankton, microalgae, cyanobacteria, and fish.

The German Environment Agency has recently concluded that scrubber washwater discharge "poses an unacceptable risk."

The Legal Landscape of Scrubbers

The continued use of scrubbers is also legally dubious.

Under the EU Water Framework Directive (Article 4), member states are legally obliged to prevent deterioration of their water bodies and reduce pollution from priority hazardous substances—many of which are found in scrubber discharge.

Also, the Marine Strategy Framework Directive (e.g. Article 1) requires a precautionary approach to marine protection. Permitting scrubber use, especially nearshore, flies in the face of these obligations.

Similarly, the United Nations Convention on the Law of the Sea (UNCLOS, Article 195) requires states to protect the marine environment from all sources of pollution. States must ensure that damage or hazards are not shifted, directly or indirectly, from one area to another, nor that one type of pollution is merely transformed into another.

Allowing ships to dump toxic washwater in sensitive marine areas raises serious questions about whether these obligations are being met.

MARPOL Annex VI (Regulation 4.4) permits the use of "equivalent" technologies only under the condition that they do not impair or damage the environment, human health, property, or the resources of other States.

Given the documented environmental risks associated with scrubber discharges, it is difficult to see how their use can be considered compliant with this provision.

Recent Bans on Scrubber Washwater Discharges

Given the limited pace of action by the International Maritime Organization (IMO) as the global regulator of shipping, it is both legitimate and necessary for individual states or regional bodies, like OSPAR, to adopt complementary measures addressing the use of scrubbers.

The science is clear. The legal obligations are binding. And cleaner alternatives exist.

It's no surprise, then, that a growing number of regions are taking action. E.g. Denmark, Finland and Sweden are already banning scrubber washwater discharges in its territorial waters since summer 2025.

Several major ports and regional authorities have already imposed their own restrictions. Recently, e.g. the OSPAR Commission for the North-East Atlantic decided to prohibit the discharge of scrubber washwater in internal waters from 2027 onwards.

This is a policy wave that's gaining momentum—and for good reason.

It's time for governments, regional regulators, and port authorities around the globe to follow the lead of Denmark and others by implementing full bans on scrubber washwater discharges.

Neglecting Peer-Reviewed Science

Despite a growing body of peer-reviewed evidence and an increasing number of regulatory restrictions around the world, the industry's main lobby group continues to downplay scientific findings to defend the status quo.

That an organization naming itself the Clean Shipping Alliance is devoted to defending scrubbers and the continued use of heavy fuel oil is, at best, ironic. The group's name suggests a commitment to clean seas, yet its actions support the prolonged use of the dirtiest fuels available.

While the extent of environmental harm from scrubber discharges can be debated, there is no serious argument that this practice represents clean, cleaner or by any means sustainable shipping.

Clean Shipping Alliances criticism to OSPAR's decision to ban scrubber washwater discharge relies on misleading timelines, a denial of peer-reviewed science and a legal misinterpretation of OSPAR's rights and obligations under environmental law.

Their cherry-picked studies and often industry-funded research with known limitations, typically assumes high dilution, short exposure times, and ignore cumulative or long-term effects.

In a Nutshell

Scrubbers exist to protect the profits of companies unwilling to invest in cleaner alternatives, not to protect the environment or public health.

Not only at the expense of human health and the environment but also at the expense of competitors that switch to cleaner fuels. If we see two ships next to each other the one with the scrubber is always worse for the environment, because the ship without scrubber complies with regulation by using a less toxic fuel and therefore posing decreased risk to health and nature.

A ban of heavy fuel oil moreover prohibits oil pests with their devastating environmental impact.