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Holland America Lines test seawater-scrubbing of diesel exhausts on cruise ship

Massive sulphate disposal in seawater, is it safe, or will history repeat itself?

Walter Schneider

According to announcements by Holland America Cruise Lines and by Kristallon (the maker of the scrubber) [1] earlier this year and later, one of the best solutions ever devised to reduce and curb cruise-ship-engine emissions, and thereby[2] the massive sulphur-dioxide (SO₂) pollution produced by cruise ships, was about to be tested and is undergoing testing right now, with promising results.

The seawater scrubber on the cruise ship Zaandam (Inland route Vancouver to Alaska) will use 450 tonnes of seawater an hour to help convert SO₂ to sulphuric acid (H₂SO₄) and to sulphate (SO₄^2-). The altered seawater from the conversion of the SO₂ by the seawater scrubber will be discharged - diluted at a ratio of 1:10 - into the ocean. The conversion of the remaining sulphuric acid contained in the discharge water will then be completed in the ocean, to convert the remaining sulphuric acid to sulphate.

In essence, such a conversion process will do what nature does anyway, but it will take a shortcut and eliminate atmospheric pollution and the impact of acid rain caused by cruise-ship emissions. When SO₂ is discharged into the air, it is transformed into sulphur-trioxide (SO₃) and then, upon contact with water in the air, changed to sulphuric acid and into sulphate. That produces acid rain.

A diesel-powered ship equipped with a seawater scrubber will locally discharge concentrated “acid rain” right into the ocean and, where a cruise ship cannot connect to an on-shore source of electric energy (there are none on the Vancouver-Alaska route), right into the water of the harbour where it is berthed.

Various studies that were commissioned to examine the issues involved concentrated on the “acid rain” issue. They mention sulphate-production and -dumping only in passing, if at all. Those studies that mention sulphate consider it to be harmless, but is it?

Sulphate is a source of oxygen for anaerobic bacteria. Anaerobic bacteria metabolize sulphate and produce, amongst other things, hydrogen-sulphide (evil-smelling in small concentrations and scentless but harmful and even extremely deadly in moderate concentrations). Aside from the fact that the dumping of sulphate causes anaerobic bacteria to thrive in seawater at the bottoms of bodies of water that are starved of oxygen (common in coast waters), the anaerobic bacteria cause a concern that none of the seawater-scrubber studies I examined mention at all.

Anaerobic bacteria that metabolize sulphate convert the all-pervasive mercury in water (its presence there being largely a result of atmospheric distribution of pollution by coal-fired power plants) to a form (methyl-mercury) that is bio-available but not bio-degradable. The danger of methyl-mercury in the biomass is that it becomes concentrated as it moves up through the food chain — by a factor of about 10 every time it passes from one level to the next. At times and in some localities methyl-mercury causes fish (who are one step removed from the top of the food chain) that are contaminated with excessive levels of methyl-mercury to become unsafe to eat.

Methyl-mercury poisoning in humans who regularly ingest fish or shellfish was first discovered in 1956 in Japan, where it produced [3] the infamous Minamata disease and its devastating results. [4] Minamata disease also manifested itself many years later in Canada, in humans that lived, and regularly ate fish, in areas downstream from pulp mills.

Are seawater scrubbers on cruise ships safe for humans? Who knows? One thing is certain. Although the cause of Minamata disease was known for many years, prior to 1970 it was not considered in calculating its impact on humans when pulp mills using mercury-polluted bleach and discharging mercury-polluted water into streams were constructed in Canada.

Minamata disease in Ontario, Canada, was discovered in 1970. The human misery and costs caused by Minamata disease in Ontario were enormous.

There are many settlements along the Inland Route to Alaska that subsist on fish. There are others that sell fish to the whole world. Will seawater scrubbers on cruise ships keep all consumers of fish from that area safe? Who knows? One would think that is worth taking a look at.

However, as of now it does not appear that anyone involved in studying seawater-scrubbing of diesel exhausts of any ship is looking beyond the goal of preventing most or all SO2 produced by ships from entering the atmosphere. The impact that the injection of a massive volume of sulphate will have on the local ecology in coastal waters, in relation to giving anaerobic bacteria a boost that will enable an escalation of the rate of conversion of precipitated mercury to methyl-mercury, appears not to be an issue that is being examined in connection with sulphate production by seawater scrubbers. Nevertheless, the relationship of anaerobic bacteria thriving on sulphate and causing an escalation of the production of methyl-mercury in the process is a fact. For example:

Coastal Environmental Quality Initiative, University of California
[5] Contribution of Iron-Reducing Bacteria of Mercury Methylation in Marine Sediments, by Emily J. Fleming and D C. Nelson; Paper 040, Dec. 8, 2006 (212 kB PDF file)

Quote: [methyl-mercury] enters food chains where it bioaccumulates to concentrations that can cause impaired neurological function in a variety of higher organisms (fish, birds, humans). This toxic conversion has, in the scientific literature, been quite dogmatically attributed to activities of sulfate-reducing bacteria….

[6] More reports and study reports can be accessed through a google-search (about 364 entries on the search-return list)

There may not be any cause for concern with the environmental impact of seawater scrubbers, but it is possible that it exists. If that is the case, and if seawater scrubbers still are permitted to be used, then many people will become severely and incurably ill, and ultimately the taxpayers will be left holding the bag.