Research results

The international maritime shipping industry contributes to air pollution, particularly in coastal areas and port cities. The ‘International Convention for the Prevention of Pollution from Ships’ regulates, among other things, air pollution from shipping and sets limits for the sulphur content in fuels. Many ships are therefore equipped with exhaust gas cleaning systems (EGCS) – or scrubbers for short – to reduce sulphur oxide emissions. Around 25 percent of the global shipping fleet uses this technology. In a comprehensive study, a research team led by Prof Christine Achten from the University of Münster, in cooperation with the German Federal Maritime and Hydrographic Agency, has now examined the wastewater from such scrubber systems for its contamination with polycyclic aromatic hydrocarbons (PAH) and their toxic effects. This is one of the most comprehensive studies on this topic. The research results were published in the journal ‘Marine Pollution Bulletin’.

Scrubber systems are based on a process in which water is sprayed into the ship’s exhaust gases to ‘scrub’ the sulphur from the emissions. While open-loop systems usually discharge the wastewater directly into the sea, closed-loop systems keep the scrubbing water and an alkaline solution circulating within the system. Yet even in closed-loop systems, most of the wastewater is disposed of in the sea – or on land in a few exceptional cases. Many of the pollutants removed in this way end up in the sea via the scrubber’s wastewater. These include PAH, a group of pollutants that often contains toxic compounds that are poorly biodegradable.

PAH are produced during incomplete combustion processes of organic material and are components of fossil fuels. The entire group of substances is estimated to comprise thousands of organic compounds. This large number of compounds makes the analysis and regulation of PAH difficult. In 1976, the US Environmental Protection Agency (EPA) selected 16 PAH compounds and included them in its ‘List of Priority Pollutants’. Since then, these 16 compounds have been frequently analysed in environmental studies. Christine Achten criticises this approach, explaining that “the 16 EPA PAH are not the most toxic compounds in many study areas. It is important therefore to look at other compounds as well. This is what we did in our study.”

The research team analysed wastewater samples from four ships between 2020 and 2023 for PAH contamination. In addition, the chemical results were supplemented with studies on the ecotoxicological effects of the substances under investigation. The researchers analysed samples from open and closed circuits, as well as the fuels used. They used various mass spectrometry methods for this purpose. The team analysed all samples for 71 specific PAH and also applied a so-called non-target method, which allowed them to detect further compounds. The results revealed that the identified PAH predominantly do not originate from combustion, but from the fuel used, and that they are alkylated PAH derivatives. This observation is consistent with the finding that the level of PAH contamination and toxicity depend on the fuel used. Alkylated PAH are associated with increased toxicity to fish, but are much less well studied than the 16 EPA PAH.

The wastewater from the closed-loop system had higher PAH concentrations than that from the open-loop systems, in particular the highly toxic, high-molecular PAH from combustion processes. “From an environmental point of view, a shift in pollutant inputs from air to water is unacceptable,” summarises Christine Achten. The research team therefore recommends the use of marine fuels with low PAH concentrations. In addition, the results emphasise the importance of comprehensive PAH analysis and show that the 16 EPA PAH are also not representative for the assessment of scrubber effluents and must be supplemented by further PAH.

The project received funding from the German Federal Environment Agency (UBA). In February 2023, the project report ‘Environmental Impacts of Discharge Water from Exhaust Gas Cleaning Systems on Ships’ was published with the participation of the University of Münster. In the study, which appeared in the journal ‘Marine Pollution Bulletin’, Christine Achten and her team carried out additional analyses and a comprehensive data evaluation.

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Wissenschaftlicher Ansprechpartner:
Prof. Dr. Christine Achten
University of Münster
Institut für Geologie und Paläontologie
Phone: +49 251 83-36170
E-Mail: achten@uni-muenster.de

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Originalpublikation:
Christine Achten, Octavio Marin-Enriquez, Brigitte Behrends, Sandra Kupich, Andreas Lutter, Richard Korth, Jan T. Andersson (2024): Polycyclic aromatic compounds including non-target and 71 target polycyclic aromatic hydrocarbons in scrubber discharge water and their environmental impact. Marine Pollution Bulletin; https://doi.org/10.1016/j.marpolbul.2024.116790

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Weitere Informationen:
https://www.uni-muenster.de/GeoPalaeontologie/en/angewandtegeologie/forschung/index.html Achten Lab (Applied Geology)