Freight ship
Scrubber-water from shipping is shown to be toxic.
Photo: Jens Rademacher, Unsplash

Closed-loop scrubber water still affects marine life

By washing - or scrubbing - exhaust from ships in a fine spray of seawater, emissions of acidifying sulphur oxides to the atmosphere are reduced. However, the water is very acidic and can contain heavy metals and organic pollutants. New research shows that water leakages affect the survival, diversity, and reproduction of marine zooplankton.

Stricter global limits for sulphur content in marine fuels apply since January 2020 and ships can comply by using a fuel with low sulphur content or by installing an exhaust gas cleaning system, also known as a “scrubber”.

Many ports and states have banned the use of open-loop scrubbers, in which wastewater is continuously discharged back to the sea, and attention has recently also been drawn to closed-loop scrubbers. Although closed-loop scrubbers recirculate the wastewater, they can also generate a concentrated bleed-off of 150 m3/day that contains many harmful substances such as PAHs and heavy metals.

FRAM researchers Christina Jönander and Jenny Egardt presented new research on how this affects marine life at this year's annual science conference of the International Council for the Exploration of the Sea (ICES).

Jenny håller upp ett provrör med havsvatten.
Jenny Egardt taking water samples on an earlier expedition.
Photo: Christina Jönander
Christina Jönander
Photo: GU

In their research, they found effects of <1.5% closed-loop scrubber water on marine mesozooplankton survival, diversity, and reproduction, as well their ability to predate on microzooplankton, independent of their seasonal species composition.

"We estimated that the total chemical concentration in the closed-loop scrubber is at least 17 times higher than what is known to be toxic to zooplankton, and that the toxicity is driven both by metals, such as vanadium, copper, nickel, and zinc and PAHs (polycyclic aromatic hydrocarbons.)", says Christina.

Christina and Jenny presented their results in the themed session called 'Steering shipping impact prevention towards holistic marine management'. The title of their presentation was: Trophic interactions in marine zooplankton exposed to closed-loop scrubber water