Seawater contamination associated with in-water cleaning of ship hulls and the potential risk to the marine environment

Highlights: • In-water cleaning effluent was highly contaminated with antifouling paint residues. • Particles with sizes of ≥8 μm contributed up to 94% of the particulate residues. • Dissolved Cu and Zn in the effluent were at levels lethal to marine organisms. • Model predicted environmental concentration was higher than no-effect concentration. • Untreated discharges of the effluent pose clear risks to the marine environment. In-water cleaning can clear-off foulants from ship hulls to prevent transportation of non-indigenous species and reduce hull friction and consequent fuel use. However, during cleaning, antifouling paint residues containing toxic substances can be released into the environment. To understand the potential risks of in-water hull cleaning, cleaning effluents were collected and analyzed for total suspended solid (TSS), particle size distribution, and metal concentrations. TSS concentrations were 97.3–249 mg/L, corresponding to release rates of 12.9–37.5 g/m² from the hull surface. Particles with sizes of ≥8 μm contributed 75–94% of the TSS. Average Cu and Zn concentrations in the effluents were 209 μg/L and 1510 μg/L, respectively, which were used for risk assessment in two port scenarios. Although the risks vary with the scale of the hull cleaning and the ports, in-water cleaning poses clear risks to marine environments, unless the effluents are recovered or treated before being released.