ICES highlights risks associated with ships' scrubber discharge water

Recommendations to tackle the emerging global problems associated with ships' scrubber discharge water is the focus of ICES latest Viewpoint.
Published: 24 September 2020

​​​​Air pollution from maritime transportation is a major environmental pressure. Sulph​ur oxides released from the burning of marine fuels react with water in the air to form acid rain and are responsible for a variety of health and environmental impacts. In 2008, the International Maritime Organization (IMO) adopted regulations to control air pollution fro​m ships, stipulating a progressive reduction in the emissions of sulphur oxide until 1 January 2020, when a maximum 0.50% of emissions could comprise sulphur oxides.   

To comply with these limits, ships should switch to a fuel with lower sulphur content or install an exhaust gas cleaning system, also known as a scrubber.

The price difference between heavy fuel oil and low sulphur fuels has meant that an increasing number of ships have opted to install scrubbers. The installation of a scrubber allows for the continued use of lower cost fuels that have higher sulphur content. Within the scrubber, the exhaust gas passes through a fine spray of alkaline water which readily dissolves sulphur oxides so that levels are sufficiently reduced in air emissions. Nitrogen oxides, and other contaminants are also washed out. However, the resulting scrubber discharge water is a chemical cocktail of acidifying, eutrophying, and contaminating substances and elementsThe impacts of scrubber discharge water can be completely avoided through the use of alternative fuels, such as distilled low sulphur fuels. Distilled fuels have the added benefit that they remove the threat of heavy fuel oil spills from shipping activities.

ICES response
Discussions had taken place within the IMO to emphasize that air pollution was not just transferred to the marine environment. However, while the number of ships with installed scrubber systems is increasing, scrubber discharge water remains poorly regulated. 

It is in response to the lagging legislation that ICES releases our latest Viewpoint. This has been developed by a ​collaboration between members of our expert groups on Shipping Impacts in the Marine Environment (WGSHIP), Marine Chemistry (MCWG), Biological Effects of Contaminants (WGBEC), and Marine Sediments in Relation to Pollution (WGMS).

A background report details the consequences and impacts of scrubber discharge water, including immediate mortality in plankton, negative synergistic effects, and further impacts through bioaccumulation, acidification and eutrophication in the marine environment.

Ida-Maja Hassellöv, co-chair of WGSHIP also thinks that the Viewpoint on scrubbers reflects the timely startup of her group, which had its first meeting in November 2019. "Worldwide, there is an increasing awareness and interest regarding the impact from shipping on the marine environment. WGSHIP gathers researchers working on this topic in 13 different countries and in addition we have a broad network within ICES, which facilitated interaction with other relevant expert groups. To assess the environmental impact of scrubber discharge water, competence within many different marine disciplines is required, and I am happy that we managed to have such a good collaboration within the group."


ICES recommends that if the use of alternative fuels is not adopted, and scrubbers continue to be considered an equivalent method to meet the sulphur emissions limits, then there is urgent need for significant investment in technological advances and port reception facilities to allow zero discharge closed loop scrubber systems, improved protocols and standards for measuring, monitoring and reporting on scrubber discharge water acidity and pollutants, and evidence-based regulations on scrubber water discharge limits that consider the full suite of contaminants.

An initial response from the IMO to the background report was that, it provides helpful input to the discussion on exhaust gas cleaning systems discharge water”.

Mark Dickey-Collas, Chair of ICES Advisory Committee will formally present this viewpoint to the IMO in 2021. Noting the importance of the translation of science into advice Dickey-Collas states, “ICES viewpoints enable scientists to highlight the evidence that impacts important societal issues. We use viewpoints to comment and advise on human impacts on and services from the marine environment. This viewpoint on scrubbers is very timely as we propose to submit it to the IMO in the spring of 2021.” 

​​Published online

ICES VIEWPOINT: Scrubber discharge water from ships – risks to the marine environment and recommendations to reduce impacts and the supporting report, ICES Viewpoint background document: Impact from exhaust gas cleaning systems (scrubbers) on the marine environment, are now available on ICES website.

​​​​​Incorporating innovation is a priority area for ICES Advisory Plan.  Supporting the translation of mature science into Viewpoints incorporates new knowledge into the advisory process to contribute effectively to the creation of advice on meeting conservation, management, and sustainability goals. Read more about ICES advice priority areas in ICES Advisory Plan

The background document for this viewpoint was developed by Ida-Maja Hassellöv (Chalmers University of Technology), Marja Koski (DTU Aqua), Katja Broeg (Ger​man Federal Maritime and Hydrographic Agency), Octavio Marin-Enriquez (Ger​man Federal Maritime and Hydrographic Agency), Jacek Tronczynski (Ifremer), Valérie Dulière (Royal Belgian Institute of Natural Sciences), Cathryn Murray (Fisheries and Oceans Canada), Sarah Bailey (Fisheries and Oceans Canada), Jessica Redfern (Anderson Cabot Center for Ocean Life), Karen de Jong (Institute of Marine Research, Norway), Emmanuel Ponzevera (Ifremer), Maria Jesus Belzunce-Segarra (AZTI), Claire Mason (Cefas), Josephine C. Iacarella (Fisheries and Oceans Canada), Brett Lyons (Cefas), Jose A. Fernandes (AZTI) and Koen Parmentier(Royal Belgian Institute of Natural Sciences​).​


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​Discharge of scrubber water his a growing concern worldwide.


​What is an ICES Viewpoint?

Viewpoints allow our expert groups to draw attention to the consequences of new knowledge for society and the management of marine activities. This highlights our capacity to provide impartial evidence-based analyses of emerging topics related to the state and sustainable use of the seas and oceans, as well as raising awareness of the opportunities to apply ICES science.

​To provide a thorough and effective review of the underlying science and data, and to ensure they are impartial, viewpoints are developed in much the same way as ICES advice. Once a topic is identified as being of potential importance to managers and society, a background science document is prepared by our expert group network which is then peer-reviewed. Based on this, an advice drafting group is convened to draft​ a viewpoint which then needs to be reviewed and signed-off by ACOM. This process guarantees that viewpoints receive the same levels of quality control as ICES advice.

The number of ships with scrubbers (in operation and on order) worldwide increased following reduced IMO limits on sulphur emissions (January 1, 2020; red line). Source: DNV- GL Alternative Fuels Insight. 6 July 2020.
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ICES highlights risks associated with ships' scrubber discharge water

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