A novel method to assess the dilution of complex mixtures in the marine environment: Application to marine scrubber water effluents

A new method is introduced that, using water-quality modelling results focused on single substances, estimates the degree of the progressive dilution and degradation of a complex mixture after discharge in the marine environment, until its consistency is modified due to different biogeochemical processes acting on its constituents. The method is based on the variance between the dilution ratios of scrubber water constituents and is applied to scrubber water effluents in two case studies in the Mediterranean Sea, using both Eulerian and Lagrangian frameworks. Results reveal that, prior to the onset of biogeochemical transformations, scrubber water behaves as a homogeneous mixture through turbulent mixing with surrounding water, gradually diluting to 10 −5 –10 −10 ratios, in spatiotemporal scales ranging from 2 to 25 km and 2 to 60 h. The proposed method generates scrubber-water dilution maps, directly comparable to the results of “whole effluent” ecotoxicological experiments, making them suitable for risk and impact assessment studies. • A new method enables comparison of water quality model to WET ecotox studies results. • A variance-based criterion is defined to determine “whole effluent” stage of the mixture. • Turbulent mixing predominates prior to the onset of biogeochemical transformations. • Scrubber water (SW) dilutes to 1:10 5 –1:10 10 ratios, between 2 and 25 km, 2–60 h. • SW presence maps are produced, comparable to WET ecotox experiments results.