Wastes from international shipping: ecotoxicological assessment of scrubber water in Unicellular Algae (<i>Tetraselmus Suecica</i>) and Blue Mussel (<i>Mytilus Edulis</i>) larvae

Wastes from shipping pose a substantial environmental challenge at local, regional and global scales, particularly in terms of adverse impacts on climate change and biodiversity. There is an increase in installations of exhaust gas scrubbers to reduce the emissions from ships following international regulations on sulphur content in marine fuel from 2020. On the basis of their operation, marine scrubbers can be classified into wet and dry scrubbers. Wet scrubbers are classified into closed- or open-loop scrubbers. The type of scrubber used presents different advantages and disadvantages but scrubber water (also known as washwater) from both wet scrubber systems has been found to release acidic water containing nutrients and contaminants back to the marine environment, including heavy metals, aromatic hydrocarbons, and soot particles. This is especially true for the open-loop scrubbers that utilize the natural alkalinity of seawater and keep a high flow of process water in order to reduce SO2 in the exhaust and the washwater is discharged to sea, most often without substantial treatment. Despite increasing use of scrubbers, little is known about potential impact of the discharged washwater on the marine environment. Pollutants such as polycyclic aromatic hydrocarbons (PAHs) and metals (such as vanadium, nickel, lead) are part of the washwater discharge. In ecotoxicological tests, a number of marine organisms have shown negative effects after acute and chronic exposures to varying concentrations of scrubber water, but the main pollutants involved in these responses are not clear yet. The aim of this study was to evaluate the effect of the main pollutants found in open-loop scrubber discharge water for survival, feeding and development of different species at the base of the food web after acute exposures to gas scrubber effluent. Toxicity, mortality, and physiology have been evaluated in marine microalgae, Tetraselmis suecica, and blue mussel (Mytilus edulis) larvae. Direct exposure to scrubber water appears to adversely affect biological and reproductive parameters in invertebrates, raising substantial concerns about ongoing open-loop exhaust gas scrubber system deployment