Anna Lunde Hermansson: Ship scrubbers continue to pollute the Baltic Sea

Exhaust gas cleaning systems, also known as scrubbers, are installed on ships to enable a continued use of cheap residual high sulphur fuel oil while still being compliant with the International Maritime Organization’s (IMO’s) stricter limit in sulphur emissions to air. The most common scrubber, the open loop system, continuously pump onboard ambient seawater, which is sprayed over the exhaust where sulphur oxides and several other contaminants are being scavenged. The scrubber effluent, now highly acidic and containing high concentrations of heavy metals and organic combustion products, is then discharged directly back into the marine environment. While ready-to-use alternatives (e.g. low sulphur fuels) exists, these are generally substantially more expensive which is why an increasing number of shipowners are opting for the use of scrubbers on their vessels. Today, over 6000 vessels, consuming a substantial share (~25%) of the total bunker fuel demand globally, are operating with scrubbers, thus using high sulphur heavy fuel oil (HFO) as their main fuel. In the Baltic Sea, the number of ships operating with a scrubber have multiplied since 2015 since the implementation of the Baltic Sea as a Sulphur Emission Control Area (SECA), with the goal of reducing pollution. Research show that the growing scrubber fleet has resulted in an increased HFO consumption in this designated SECA, and since 2015, almost 10 million tonnes of HFO have been used and over 3 billion cubic meters of open loop scrubber effluents have been discharged within the Baltic Sea area.

Ecotoxicological studies, where marine organisms at different life stages are exposed to different dilution ratios of whole scrubber effluents, reveal adverse effects at extremely low concentrations. Larval development is among the most sensitive life-stages, meaning that the discharge of scrubber effluent can seriously threaten the recruitment at several trophic levels. When attempting to predict the toxicity of scrubber effluents, by summing up the predicted effects of known scrubber effluent constituents, it is evident that the toxicity is always underestimated. Even when more substances are added to the prediction, by applying computational methods to estimate adverse effects on substances where we do not have ecotoxicological data, the measured effects are observed at much lower concentrations. This suggest that there are other substances in scrubber effluents, currently not monitored and/or measured, that result in adverse effects and, additionally, this shows that the complex mixture may be more potent than the sum of its constituents due to synergistic effects.

When the societal damage cost from scrubber water discharges was estimated for the Baltic Sea, the cumulative damage cost amounted to € 680 million between 2014-2022. The damage cost was calculated based on cost estimates from a willingness-to-pay study in combination with toxicity potentials and characterization factors calculated from a life cycle impact assessment model, yielding a price per cubic meter of discharged open loop scrubber effluent. The damage cost estimate is however an underestimate, only including a limited number of substances detected in scrubber effluents. Also, a review of the willingness-to-pay study and the toxicity potential show that damage cost of the currently included substances is likely to be higher.

A growing number of scientific publications show that the use of scrubbers will never be a sustainable solution but merely an economically motivated strategy to enable a continued use of the cheapest, and also the dirtiest fuel that exist on the market. Finland, Sweden and Denmark are taking action to ban the discharge of (open loop) scrubber effluents within their territorial waters and more countries within the Baltic Sea have limited the discharge of scrubber effluents at different spatially defined levels. HELCOM and its Member States should continue their strong collaboration to cease discharge of all scrubber effluents and the combustion of HFO within the Baltic Sea. Given the long-term strategic goals and resources invested in reducing the pressures from human activities within the Baltic Sea area, restricting the use of scrubbers and HFO, where readily available alternatives exist, is one measure that will have huge impact, both for the marine environment and from a socioeconomic perspective.