Newswise — According to a recent study conducted by Chalmers University of Technology in Sweden, the collective release of metals and other environmentally harmful substances by ships poses a significant threat to the marine ecosystem. The researchers assessed the pollution levels caused by these emissions in four ports and discovered that over 90 percent of the contaminants originated from the water discharged by ships' scrubbers, which are designed to cleanse their exhaust fumes.
Anna Lunde Hermansson, a doctoral student at Chalmers' Department of Mechanics and Maritime Sciences, emphasizes the importance of stricter regulations regarding the discharge water from scrubbers. She states, "The findings are clear and undeniable. Implementing more stringent controls on scrubber discharge water is essential to mitigate the degradation of the marine environment."
In the conventional approach, environmental risk assessments (ERA) of shipping emissions have focused on evaluating one emission source at a time. For instance, an ERA might examine the risks associated with copper found in antifouling paints. However, similar to other industries, shipping involves numerous emission sources that contribute to overall environmental impact.
According to Anna Lunde Hermansson, who conducted the study along with her colleagues Ida-Maja Hassellöv and Erik Ytreberg, a single ship generates a variety of emissions encompassing greywater, blackwater (discharges from showers, toilets, and drains), antifouling paint, and scrubber discharge water. Consequently, it becomes crucial to examine the cumulative environmental risk posed by shipping activities in ports. Their study takes a cumulative perspective to assess emissions from shipping and their potential impact on the environment.
A scrubber is a system designed to clean the exhaust gases produced during the combustion of heavy fuel oil, which has been the predominant fuel choice for ships since the 1970s. It functions by pumping seawater and spraying it over the exhaust gases, effectively preventing the release of airborne sulphur emissions into the atmosphere. This process helps to reduce the environmental impact of ship emissions by minimizing the amount of sulphur compounds reaching the air.
Scrubbers have become a solution for ships to meet the requirements established by the International Maritime Organization (IMO) in 2020. However, there is a significant issue associated with this approach. While scrubbers effectively remove sulphur from the exhaust gases, the water used in the process becomes contaminated with not only sulphur but also other harmful substances like heavy metals and toxic organic compounds. This leads to the acidification of the scrubber water. Unfortunately, the common practice is to discharge the contaminated scrubber water directly into the sea, which poses a potential risk to the marine environment.
Hundreds of cubic metres of contaminated water every hour
According to Lunde Hermansson, the current practice of discharging heavily contaminated scrubber water directly into the sea lacks an intermediate cleaning step. As a result, a single ship can pump out several hundred cubic meters of such water per hour. While new guidelines for Environmental Risk Assessments (ERAs) of scrubber discharges are being developed, the existing assessments still focus on evaluating one emission source at a time. This approach fails to provide a comprehensive assessment of the overall environmental risk posed by shipping emissions, highlighting the inadequacy of the current evaluation process.
In the recent study conducted by researchers at Chalmers University, the team examined four distinct port environments to analyze the concentrations of contaminants originating from five different sources. The study utilized real-world data from Copenhagen and Gdynia, which were chosen based on their significant shipping traffic volumes and a considerable percentage of ships equipped with scrubbers. These ports were selected as representative locations to assess the impact of shipping emissions and scrubber usage on contaminant concentrations in the marine environment.
The findings of the study indicated that the cumulative risk levels in the examined ports exceeded the acceptable risk threshold by a significant margin. Specifically, the risk levels in two of the ports were five and thirteen times higher than the defined limit for acceptable risk.
For the remaining two port environments, internationally recognized port descriptions were employed in the Environmental Risk Assessments (ERAs). One of these ports was representative of a typical Baltic Sea port, while the other represented a European port characterized by efficient water exchange owing to a substantial tidal range. These ports were included to provide a broader understanding of the cumulative risk levels in different types of port environments and their implications on the marine ecosystem.
The scientists discovered that three of the four harbor settings exhibited susceptibility to unacceptable dangers based on the utilized evaluation framework. They additionally observed that the most elevated levels of dangerous substances in the marine ecosystem and the greatest contribution to the risk were attributed to emissions from antifouling paint and scrubber discharge water. Over 90% of environmentally hazardous metals and PAHs (polycyclic aromatic hydrocarbons) originated from scrubber discharge water, whereas antifouling paints carried the largest burden of copper and zinc.
Total load is what causes the damage
"By focusing solely on a single source of emissions, the likelihood of environmental harm may appear minimal or tolerable. However, when multiple individual emissions sources are considered together, the resulting risk becomes unacceptable. Marine organisms, which are exposed to various contaminants and toxins, are indifferent to the origins of these substances; it is the cumulative load that inflicts the harm," stated Lunde Hermansson.
Among the port environments examined in the researchers' ERA, only the one characterized by the greatest water exchange per tidal period demonstrated an acceptable level of risk. This implies that a significant volume of water is regularly exchanged within the port as the tides ebb and flow.
"It is crucial to bear in mind that contaminated water does not simply vanish; it is carried elsewhere. Within the port environments under examination, there might be a certain level of acceptance regarding environmental harm—acknowledging that within this specific environment, we have chosen to accommodate industrial activities despite the resulting pollution. However, when the contaminated water is eventually flushed out into the ocean, it can reach pristine marine areas and trigger even more significant repercussions. This is a matter that we address in our research. We assess the cumulative load, focusing on the actual amount discharged into the environment," explains Lunde Hermansson.
The presence of scrubbers on a ship is not obligatory. They are installed and utilized as an alternative to transitioning to cleaner yet more costly fuels that emit reduced quantities of metals and PAHs. Scrubbers enable ships to persist in using the significantly cheaper and more environmentally detrimental heavy fuel oil. Heavy fuel oil is a residual byproduct derived from the distillation of crude oil and is exclusively employed in maritime transportation.
Economical to install scrubbers
Starting from the mid-2010s, there has been a noticeable rise in the installation of scrubbers on ships. According to a study conducted in 2018, it was determined that there were 178 ships equipped with scrubbers actively operating in the Baltic Sea. Presently, researchers estimate that the number has tripled since then. On a global scale, approximately 5,000 ships, which accounts for around five percent of the total fleet, are equipped with scrubbers.
"However, it is the larger ships with substantial fuel consumption that opt for scrubber installations, as it proves to be more cost-effective for them. Consequently, we expect that these ships would contribute to approximately 30 percent of the overall fuel consumption in the shipping industry," explains Lunde Hermansson.
Lunde Hermansson highlights the contradiction between the utilization of heavy fuel oil as ship fuel and the commitments set by the International Maritime Organization (IMO), which aims to reduce greenhouse gas emissions from shipping by 50 percent by 2050. To address this concern, the Swedish Agency for Marine and Water Management, along with the Swedish Transport Agency, has presented a proposal to the Swedish Government, suggesting a prohibition on the discharge of scrubber water into internal waters, specifically referring to the waters within the Swedish archipelago. This proposal aims to mitigate the potential environmental impact caused by the discharge of scrubber water in sensitive areas.
Erik Ytreberg, an associate professor at the Department of Mechanics and Maritime Sciences at Chalmers, acknowledges that the proposed ban on the discharge of scrubber water into internal waters is a positive step forward. However, he expresses the desire for a more comprehensive ban that covers larger marine areas. He recognizes the difficulty for individual countries in regulating international shipping, considering the global nature of the industry.
More about the research
The article titled "Cumulative environmental risk assessment of metals and polycyclic aromatic hydrocarbons from ship activities in ports" has been published in the journal Marine Pollution Bulletin. The authors of the article are Anna Lunde Hermansson, Ida-Maja Hassellöv, and Erik Ytreberg, all affiliated with the Department of Mechanics and Maritime Sciences at Chalmers University. Additionally, Jukka-Pekka Jalkanen from the Finnish Meteorological Institute contributed to the research. The study received partial funding from the EU project EMERGE under the Horizon 2020 funding program.
How the risk assessment in the four ports was carried out
The evaluation of environmental risk in the ports was conducted using a bottom-up approach, as depicted in the accompanying illustration.
In Step 1 To determine the loads from different emission sources in shipping, calculations were performed. The STEAM model, which evaluates emissions from ship traffic, was utilized to estimate the volumes. These volumes were then combined with specific concentrations of substances associated with each emission source, enabling the calculation of the loads for different substances.
In Step 2, The daily load obtained in the previous step was utilized to estimate the resulting concentrations in the environment, known as PEC (predicted environmental concentration). This estimation was accomplished using the MAMPEC model, which calculates PEC for a specified environment, in this case, a port. The model takes into account the properties of the substances (specifically, 9 metals and 16 polycyclic hydrocarbons) and the daily load of each substance derived from Step 1. MAMPEC calculates PEC for each substance individually, assuming a constant load.
In Step 3, To incorporate additional substances and loads from various emission sources simultaneously, the results were combined. In order to assess the environmental risk, the PEC values were compared against limit values that indicate concentrations considered safe. These limit values are known as PNEC (Predicted No Effect Concentration) and represent levels below which no detrimental impact on the marine environment is expected. If the PEC exceeds the PNEC, it signifies an unacceptable risk.
In Step 4, To provide a more comprehensive environmental risk assessment within a specific area, the risk characterisation ratios (RCRs) from multiple substances were aggregated. By adding together the RCRs, it becomes possible to calculate the cumulative risk. This cumulative risk assessment allows for a more holistic evaluation of the environmental risks present in the area.
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