ICES Viewpoint background document: Impact from exhaust gas cleaning systems (scrubbers) on the marine environment (Ad hoc)

Shipping is a diverse industry that connects the world. The distribution and intensity of commercial shipping is increasing and there is a growing need to assess and mitigate the impacts of vessel activities on the marine environment.

New global standards on sulphur content in marine fuels have led to an increasing number of ships installing exhaust gas cleaning systems (EGCS), also known as scrubbers, to reduce their emissions of sulphur oxides to the atmosphere. Ships equipped with a scrubber can continue to use heavy fuel oil, and the process results in discharges of large volumes of acidified water that contain a mix of contaminants, such as heavy metals, polycyclic aromatic hydrocarbons (PAHs), oil residues, and nitrates. For the most common type of scrubber, open loop, this polluted water is directly discharged back to the sea, trading reductions in air pollution for increased water pollution. The scrubber discharge mixture has demonstrated toxic effects in laboratory studies, causing immediate mortality in plankton and exhibiting negative synergistic effects. The sub-stances found in scrubber discharge water are likely to have further impacts in the marine environment through bioaccumulation, acidification and eutrophication. The 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. 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:

1) significant investment in technological advances and port reception facilities to allow zero discharge closed loop scrubber systems;

2) improved protocols and standards for measuring, monitoring and reporting on scrubber discharge water acidity and pollutants;

3) evidence-based regulations on scrubber water discharge limits that consider the full suite of contaminants.