Scrubber discharge water – A toxic cocktail

Chalmers University of Technology

​​The International Council for the Exploration of the Sea recommends avoidance of discharge of wash water from scrubbers. This recommendation is based on a background report produced by a group led by Ida-Maja Hassellöv, professor at Chalmers. ​On September 24, the International Council for the Exploration of the Sea (ICES) publish a so-called Viewpoint. A report that aims to provide impartial evidence-based analyses of marine science topics of potentially high importance to managers and society. This year’s Viewpoint is about effects on the marine environment as a result of wide-scale scrubber use. The recommendation is clear: do not discharge scrubber water.

A scrubber is used to clean ship exhaust gases, especially regarding sulfur oxides. By washing the exhaust gases in a fine spray of seawater, the emission of acidifying sulfur oxides to the atmosphere is reduced. However, the scrubber discharge water is very acidic and may contain other pollutants such as heavy metals and organic substances.

A fossil fuel ‘lock-in’

The Chalmers researcher Ida-Maja Hassellöv, a professor in maritime environmental science, has led the work, coordinating a group of 17 researchers from different countries to produce a background report on the effects of scrubber discharge water on the marine environment. She describes the discharge water from scrubbers as a toxic cocktail of various substances. The emissions from scrubber use are also extensive regarding metals and organic pollutants, compared with the content of other types of wastewater generated on board ships. Of the more than 8,000 vessels that operated in the Baltic Sea in 2018, less than 2% were equipped with scrubbers. Despite this, the scrubber water from these ships is estimated to have released ten to a hundred times more metals and organic pollutants to the marine environment, compared to what was released in total from all other wastewater generated on board on all 8,000 ships.
“It is really negative for the marine environment; beyond pollutants, the scrubber discharge water is often heavily acidic and sometimes contains high levels of nutrients. The use of scrubbers also means a continued opportunity for ships to burn heavy fuel oil, which means a lock-in in the use of fossil fuels. In addition, there are indications that ships’ use of heavy fuel oil can also be used to get rid of toxic waste” says Ida-Maja Hassellöv.

The consequences are difficult to survey

There are major commercial interests in scrubbers, both from manufacturers and the oil industry. Ida-Maja Hassellöv hopes that ICES’ scientific analysis and recommendation on discharges of scrubbing water from a marine environment perspective will be an important signal to, for example, the UN International Maritime Organization, IMO and governments around the world that this is something that needs to be better regulated. The consequences of the discharge of scrubber water are today difficult to assess. They include both acidifying effects, ecotoxicological effects and sometimes eutrophication.
“The effects of chemical mixtures are something that we know very little about. Last year, Christina Rudén, a professor in regulatory toxicology at Stockholm University, suggested in a government’s official investigation that all limits for toxic chemicals should be lowered to one-tenth of today’s levels because we don’t know enough about what the safe levels should be when it comes to chemical mixtures” says Ida-Maja Hassellöv.
In several ports around the world, discharges of scrubber water have been banned and in Sweden, two ports have chosen to ban discharges, but there is no national regulation in place. However, the issue is under investigation and together with her Chalmers colleagues Erik Ytreberg and Anna Lunde Hermansson, Ida-Maja Hassellöv has submitted a background report to the Swedish Transport Agency and the Swedish Agency for Marine and Water Management, which will propose a national strategy for the Government Offices this autumn.
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