Air pollution from maritime transportation is a major environmental pressure. Sulphur 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 from 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.
Instead of switching to much more expensive low-sulfur bunker oil or alternative fuels, many shipping companies have chosen to install scrubbers on their vessels. Although these wash the exhaust gases clean in a fine spray of seawater, this "washing water" is usually released directly into the sea again as a chemical cocktail of acidifying, eutrophying, and contaminating substances and elements.The chemicals are concentrated in the sea instead of spreading through the air over large areas of sea, land and lakes.
The international research organization ICES, which consists of more than 4,000 researchers from 20 member countries, 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.