ICES VIEWPOINT: Scrubber discharge water from ships – risks to the marine environment and recommendations to reduce impacts

New global standards on sulphur content in marine fuels have led to an increasing number of ships installing exhaust gas cleaning systems, also known as scrubbers, to reduce air emissions of sulphur oxides. Ships equipped with a scrubber can continue to use heavy fuel oil, resulting in significant discharge of acidified water containing several contaminants, such as heavy metals, persistent organic pollutants (POPs; mainly polycyclic aromatic hydrocarbons), and nitrogen compounds. The simplest and most common type of scrubber system, the open-loop scrubber, directly discharges the contaminated water in to the sea.

The use of scrubber systems by ships is an emerging global problem and an additional pressure on the marine environment. The substances found in scrubber 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.

The number of ships with installed scrubber systems is increasing, but legislation on scrubber discharge is lagging, inconsistent between countries, and often insufficient to protect the environment. ICES recommends the use of cleaner low-sulphur fuels, such as marine gas oil, to eliminate scrubber use and associated impacts on the marine environment. Until this is possible, ICES proposes a set of measures to mitigate scrubber impacts.