Next year, new legislation will compel international shipping to reduce sulphur dioxide emissions to air. But instead of using expensive low-sulphur fuels, the global shipping fleet is expected to install so-called scrubbers to wash exhaust emissions with seawater that is then pumped back into the sea. New research from IVL Swedish Environmental Research Institute indicates that this scrub water will have a negative effect on zooplankton.
– The new sulphur legislation is important as it reduces the impact of shipping on air quality, but unfortunately it ignores the consequences for the marine environment. If vessels continue to run on dirty bunker oil, the pollutants will instead end up in the sea where they will adversely impact the marine ecosystem, says Hulda Winnes, project manager and researcher at IVL Swedish Environmental Research Institute.
In an EU-funded study researcher at IVL have analysed the environmental effects of both open and closed scrubbing systems. The open-loop scrubber system uses large amounts of seawater to scrub exhaust gases, water that is then pumped back into the sea. The closed system recirculates the scrubbing water and discharges a lesser volume after treatment.
In ecotoxicological tests, a number of marine organisms were exposed to varying concentrations of scrubbing water. The tests were carried out in collaboration with the Norwegian Polar Institute and revealed negative effects on vital functions in several organisms. Most impacted were the copepods – a group of zooplankton that play a vital role in the food chain. Even low concentrations of untreated water from both open scrubbing systems and treated scrubber water from closed systems had adverse effects on these organisms.
Untreated scrubbing water from the open system is heavily contaminated with heavy metals, aromatic hydrocarbons and soot particles. The treated water from the closed scrubber is less contaminated and the residues that are separated are taken ashore for disposal. Discharges from open scrubbers are a greater risk for the marine environment than those from closed systems.
Individual ship passages do not impact the marine environment to any great extent, researchers point out, but in heavily trafficked waterways as well as in ports and estuaries environmental risks increase exponentially.
– Several of these pollutants break down relatively quickly but are at the same time acutely toxic. When the marine environment is continuously exposed to scrubbing water from new mercantile vessels, this acute toxicity becomes permanent. In my opinion scrubbing is a real threat to biodiversity, says Kerstin Magnusson, IVL marine ecotoxicologist and one of the authors behind the report.
– If we permit the discharge of scrubbed exhaust gases into the sea, we expose marine ecosystems to yet another source of pollution, in addition to all those they are already subject to. That conflicts with the UN global environmental goals, which require us to prevent or at least significantly reduce all kinds of pollution in the sea by 2025, says Kerstin Magnusson.
The price difference between bunker oil and low sulphur fuel is currently around $300 per tonne. Scrubber systems normally pay for themselves within a single year.
– Creating new environmental problems in this way, by giving a green light to scrubbing technology is wrong from a sustainability perspective. No comprehensive environmental studies were carried out prior to introducing the legislation. All we do when we fit exhaust gas systems, especially open-loop scrubbers, is move pollutants somewhere else, says Hulda Winnes.
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