Impact assessment of ship scrubber effluents reveals adverse effects at realistic environmental concentrations—combining a systematic review of whole effluent ecotoxicological studies with dilution modeling

Concerns regarding the potential adverse effects of ship-generated scrubber effluent discharged to the marine environment and the growing number of ecotoxicological experiments have motivated a systematic review of the available whole effluent toxicity (WET) studies where marine organisms have been exposed to scrubber effluent. All available WET studies on scrubber effluent exposure were assessed with respect to reliability and relevance, and the respective toxicity metrics (including effect concentrations and no/lowest observed effect concentration) were compiled to determine hazardous concentrations by applying a probabilistic approach. The ecotoxicological impact was assessed by relating the subsequent hazard concentrations, derived from species sensitivity distribution curves as the potentially affected fraction of species, to estimated environmental concentrations. Environmental concentrations were estimated from previous studies that have modelled scrubber effluent dilution or conducted in situ measurement of dilution of ship-generated waste. The hazardous concentration for 5% of the species was determined at 0.0003%, corresponding to environmentally realistic concentrations. Despite the wide range of confidence limits, the results indicate that the discharge of scrubber effluents, particularly from open loop systems, poses a significant environmental hazard. These findings provide a scientific basis for future risk and impact assessments of scrubber effluents, contributing to the ongoing policy discussion regarding the need to restrict scrubber water discharges.