From January 2020, the United Nations International Maritime Organization (IMO) will ban ships from using fuels with a sulphur content above 0.5%, compared with 3.5% now.The rules herald the biggest leap in how ships are powered since they switched from burning coal to oil over a century ago, but vessels will still be allowed to use higher-sulphur fuel if fitted with cleaning devices called scrubbers.  Closed-loop scrubbers keep most of the water used for sulphur removal onboard for disposal at port. Open-loop systems, however, remove sulphur coming through a ship’s smokestack with water that can then be pumped overboard.

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 results have largely been inconclusive and the IMO itself has encouraged further study into the environmental impact of scrubbers.

The stated aim of the new IMO measures is to improve human health..  A study in the journal Nature last year found ship emissions with current sulphur levels caused about 400,000 premature deaths from lung cancer and cardiovascular disease as well as around 14 million childhood asthma cases every year.

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

Excerpts from Noah Browning, Going overboard? Shipping rules seen shifting pollution from air to sea, Reuters, Oct. 21, 2019