The fumes of concern are sent below the surface

Shipping companies are now installing scrubbers on a large number of vessels around the world to meet the more stringent rules on sulfur emissions that come into effect at the turn of the year. Researchers in Gothenburg say that this method runs the risk of only transferring the environmental pollution from the air to the sea. They warn that the effects in the marine ecosystem could be serious.

​In January 2020, the limit is lowered drastically for how much sulfur global shipping can release into the air. The international maritime organization IMO has tightened the rules from a maximum of 3.5 to 0.5 per cent permitted sulfur content in the fuel. Many shipping companies now choose to install scrubbers on their vessels, instead of switching to much more expensive low sulfur bunker oil or alternative fuels. A scrubber washes the exhaust gases in a fine spray of water, which can lower the sulfur content in the air emissions to the corresponding lower level. 

Ida-Maja Hassellöv, associate professor of marine environmental science at Chalmers, is deeply concerned about the development. Not because the sulfur is moved from the air to the sea – it is converted into it sulphate which is a natural element of seawater – but because of the consequences of discharging scrubbing water into the sea has. 

​"One reason for the stricter rules is to reduce acidifying emissions sulfur oxides from ships", she says. "But scrubber use does not reduce emissions, it only concentrates it in the sea instead of spreading in the air over larger surfaces of the sea, land and lakes. When the sulfur oxides react with water and forms sulphate, it becomes heavy local acidification of the sea water."

"In addition, a number of other contaminants are washed from the exhaust, which causes scrubbing water to contain a cocktail of toxic substances. For example, we have shown that a ship can release as much copper and zinc from its scrubber as it does from its bottom paint. During certain conditions nitrogen oxides from the exhaust gases can also be washed out. For example in the Baltic Sea, this can contribute to the eutrophication problem."

So-called open scrubs are an obvious problem because they release all scrubbing water into the sea. But even most closed scrubbers, that circulate the water and add alkaline chemicals, separates some scrubbing water and releases it. They need to do this to be able to replenish with new water and alkaline chemicals. It releases smaller volumes of scrubbing water than open scrubs, but that water, on the other hand, has a higher concentration of pollutants. 

Ida-Maja Hassellöv is part of a research group at Chalmers examining how scrubbing water affects plankton, in collaboration with professor Angela Wulff's research group at Gothenburg university. They are the first researchers to do field trials on natural plankton communities. Large bags of seawater from the Stockholm archipelago is treated with scrubber water, and in parallel, the researchers do laboratory tests on individual plankton species. The results show, among other things, different Plankton species are differently sensitive to scrubbing water. It is not surprising in itself but indicates the difficulty of making complete, detailed analyses of large-scale effects of scrubber use. One particular challenge is to distinguish the effects of acidification and toxic substances when the algae are simultaneously fertilized form of nitrogen oxides.

"Nobody knows what the scrubbing water would mean on a larger scale and on a longer term", says Ida-Maja Hassellöv. "But because plankton is the basis of the entire marine ecosystem it is very scary that the number of scrubbers right now increases exponentially. Particularly when it comes to the Baltic Sea, which is already heavily burdened by environmental degradation, but this also applies to many other seas. The situation is most strained in the areas that have the most important biological productivity – that is, close to the coasts." 

Uncertainty is not only considerable when it comes to the effect of the emissions on the marine ecosystem, but also in terms of the content of different types of scrubbing water. Few independent studies have been done. An example of the lack of knowledge is that no one even knows where the metals in the scrubbing water come from. From the fuel, lubricating oils or pipelines, are some of the guesses. And the metals are an immense risk, especially in combination with acidification. A low pH causes metals to turn into free ion form, which makes them more toxic. 

The full picture is rarely discussed when it comes to scrubbing emissions, according to Ida-Maja Hassellöv. 

"Often people just talk about the sulfur itself, but that is not the real problem. As a result, scrubbers appear like a good and inexpensive way to meet the new sulfur rules. A scrubber pays off in just about 18 months compared to buying low-sulfur bunker oil."

So the need is great for more of the type of research that Ida-Maja Hassellöv is engaged in together with her colleagues Erik Ytreberg and Amanda Nylund. But in view of the scrubber boom, which is going on right now, she believes that the need for faster measures is even greater. 

"In the case of Sweden, the Swedish Transport Administration should prohibit open scrubbers in Swedish waters. China, California and some European ports have introduced such bans, and we already have enough research to justify it to Sweden. If there is a time to use the precautionary principle, it is now."

Page manager Published: Wed 10 Jul 2019.