The combined emissions of metals and other environmentally hazardous substances from ships is putting the marine environment at risk according to a new study from Chalmers University of Technology, Sweden.
When the researchers 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.
Anna Lunde Hermansson who, with colleagues Ida-Maja Hassellöv and Erik Ytreberg, is behind the new study, 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.”
The problem with scrubbers is that the wash 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. With open-loop scrubber mode, the contaminated scrubber water is 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.”
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 concluded: “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.”
The Swedish Agency for Marine and Water Management and the Swedish Transport Agency have submitted a proposal to the Swedish Government to prohibit the discharge of scrubber water into internal waters, that is, waters that lie within the Swedish archipelago.
