Microplastic and biocide release from antifouling coatings during underwater ultrasonic cleaning

Antifouling coatings are essential for controlling biofouling in the shipping industry. To improve fouling control, underwater cleaning is often employed, but this process can alter coating surfaces and release contaminants such as biocides and microplastics. This study investigates the impact of ultrasonic cleaning on an antifouling coating under controlled laboratory conditions. Commercial yacht coating samples were aged under laboratory conditions to form a leached layer and then subjected to ultrasonic cleaning with varying process parameters. Aggressive cleaning (1 cm probe-coating surface distance, 5.4 MPa acoustic pressure) significantly damaged the coating, thereby partially removing the leached layer, increasing surface roughness, and releasing microplastic particles and biocides into seawater. Gentler cleaning (4 cm probe-coating surface distance, 1.5 MPa acoustic pressure) caused no visible damage, yet microplastics and biocides were still released. Depending on cleaning conditions, the copper release ranged from 0.3 to 10 μg/cm², with similar mass amounts detected for released particles. To effectively mitigate environmental contamination, these findings highlight the importance of selecting appropriate cleaning parameters and capturing effluents during boat cleaning.