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From January 2020, the International Maritime Organization (IMO) will ban ships from using fuels with sulphur content above 0.5%, compared with 3.5% now. However, ships will be allowed to use higher-sulphur fuels if they are fitted with cleaning devices called scrubbers.

Closed-loop scrubbers keep most of the water that is used for sulphur removal on board, for disposal at the port. On the other hand, open-loop scrubbers remove sulphur with water that is pumped overboard, polluting the sea.

Years of studies have examined whether open-loop scrubbers introduce into waterways acidic sulphur harmful to marine life, cancer-causing hydrocarbons, nitrates leading to algal blooms and metals that impair organ function and cause birth defects. The impact of open-loop scrubbers still appears to be somewhat of a blind spot.

Singapore and Fujairah in the United Arab Emirates have banned the use of open-loop scrubbers from the start of 2020. China is also set to extend a ban on scrubber discharge to more coastal regions.