Severe Toxic Effects on Pelagic Copepods from Maritime Exhaust Gas Scrubber Effluents

To reduce sulfur emission from global shipping, exhaust gas cleaning systemsare increasingly being installed on board commercial ships. These so-called scrubbers extractSOX by spraying water into the exhaust gas. An effluent is created which is either releaseddirectly to the sea (open-loop system) or treated to remove harmful substances beforerelease (closed-loop system). We found severe toxic effects in the ubiquitous planktoniccopepod Calanus helgolandicus of exposure to effluents from two closed-loop systems andone open-loop system on North Sea ships.

The effluents contained high concentrations ofheavy metals and polycyclic aromatic hydrocarbons (PAHs), including alkylated PAHs. Weobserved significantly elevated mortality rates and impaired molting already in the lowesttested concentrations of each effluent: 0.04 and 0.1% closed-loop effluents and 1% open-loopeffluent. These concentrations correspond to total hydrocarbon concentrations of 2.8, 2.0,and 3.8 μg L−1, respectively, and compared to previous studies on oil toxicity in copepods,scrubber effluents appear more toxic than, for example, crude oil. None of the individualPAHs or heavy metals analyzed in the effluents occurred in concentrations which couldexplain the high toxicity. The effluents showed unexpected alkylated PAH profiles, and we hypothesize that scrubbers act as witch’scauldrons where undesired toxic compounds form so that the high toxicity stems from compounds we know very little about.

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