The combined emissions of metals and other environmentally hazardous substances from ships are putting the marine environment at risk

When researchers from Chalmers University of Technology, Sweden calculated the contaminant load from these emissions into the marine environment in four ports, it was found that water discharged from ships’ scrubbers, whose purpose is to clean their exhaust gases, accounts for more than 90% of the contaminants.

Anna Lunde Hermansson, a doctoral student at the Department of Mechanics and Maritime Sciences at Chalmers, said: “The results speak for themselves. Stricter regulation of discharge water from scrubbers is crucial to reduce the deterioration of the marine environment.”

Traditionally, environmental risk assessments (ERA) of emissions from shipping are based on one source at a time. For example, the ERA might look at the risk from copper in antifouling paints.

But as with all industries, shipping is an activity where there are multiple sources of emissions. 

Lunde Hermansson who, with colleagues Ida-Maja Hassellöv and Erik Ytreberg, is behind the new study that looked at emissions from shipping from a cumulative perspective, added: “A single ship is responsible for many different types of emissions.

“These include greywater and blackwater, meaning discharges from showers, toilets and drains, antifouling paint, and scrubber discharge water.

“That is why it’s important to look at the cumulative environmental risk in ports.”

A scrubber can be described as a cleaning system for the exhaust gases arising from the combustion of heavy fuel oil, which has been the most common fuel used in ships since the 1970s.

Seawater is pumped up and sprayed over the exhaust gases to prevent emissions of airborne sulphur reaching the air.

Scrubbers mean that ships can comply with the requirements introduced by the International Maritime Organization (IMO) in 2020.

The only problem is that the water not only takes up the sulphur from the exhaust gases, leading to acidification of the scrubber water, but also other contaminants such as heavy metals and toxic organic compounds.

The contaminated scrubber water is then often pumped directly into the sea.

Lunde Hermansson said: “There is no cleaning step in between – so up to several hundred cubic metres of heavily contaminated water can be pumped out every hour from a single ship.

“Although new guidelines for ERAs of scrubber discharges are in progress, the ERAs still only assess one source of emissions at a time, which means that the overall assessment of the environmental risk is inadequate.”



Port environments


In this new study, the researchers at Chalmers looked at four different types of port environments to determine contaminant concentrations from five different sources.

Actual data from Copenhagen and Gdynia were used for two of the ports. They were selected due to high volumes of shipping traffic, and a substantial proportion of these ships having scrubbers.

The results showed that the cumulative risk levels in the ports were, respectively, five and thirteen times higher than the limit that defines acceptable risk. 

Port descriptions used internationally in ERAs were utilised for the other two port environments. One of these environments has characteristics typical of a Baltic Sea port, while the other represents a European port with efficient water exchange due to a large tidal range.

The researchers found that three out of the four port environments were prone to unacceptable risks according to the assessment model used.

They also saw that it was emissions from antifouling paint and scrubber discharge water that accounted for the highest levels of hazardous substances in the marine environment and had the highest contribution to the risk.

More than 90% of the environmentally hazardous metals and PAHs (polycyclic aromatic hydrocarbons) came from scrubber discharge water, while antifouling paints accounted for the biggest load of copper and zinc. 

Lunde Hermansson said: “If you look at only one emissions source, the risk level for environmental damage may be low or acceptable.

“But if you combine multiple individual emissions sources, you get an unacceptable risk.

“The marine organisms that are exposed to contaminants and toxins don’t care about where the contaminants come from, it is the total load that causes the damage.”

The only port environment that showed an acceptable risk in the researchers’ ERA was the model with the highest water exchange per tidal period, meaning that a high volume of water is exchanged in the port as the tide moves in and out. 




Lunde Hermansson added: “It’s important to remember that the contaminated water doesn’t just disappear – it is transported elsewhere.

“In the port environments studied, there might be a kind of acceptance of environmental damage – that in this particular environment, we have decided that we will have an industry and that it will result in pollution.

“However, when the contaminated water is washed out to sea, it can end up in pristine sea areas and have even greater consequences.

“This is something we address in our research; we look at the total load, how much is actually discharged into the environment.”

Having scrubbers on a ship is not a requirement, but the number of ships with scrubbers installed has been on the rise since the mid-2010s. They are installed and used as an alternative to switching to cleaner and more expensive fuels that emit lower volumes of metals and PAHs.

Scrubbers allow ships to continue using the much cheaper and more polluting heavy fuel oil, which is a residual product in the distillation of crude oil, and is now used only in maritime transport.

Image: In a recently published study from Chalmers University of Technology, Sweden, the researchers used four different types of port environments to investigate the levels of contaminants emitted from five different sources. They found that the combined emissions of metals and environmentally hazardous substances into the marine environment are causing alarming levels of environmental risk to the marine habitat. Ninety per cent of the harmful emissions came from ships fitted with scrubbers, whose purpose is to clean their exhaust gases. Credit: Wikimedia Commons.

Research Aether / Earth Uncovered