Verification of the existence of copper-based antifouling paint particles in the sea and their implications for marine microplastic degradation

Abstract Marine microplastics (MP) and microdebris were retrieved from the five sampling stations between Nagasaki port and Goto Island and were classified into six types. Three of these types, MP (A), Si-based (B), and Cu-based (C) paint particles, were predominant. Type C had no depth dependence, regardless of the presence of cuprous oxide with high specific gravity. The dominant size of type C was less than 10 μm and contained 30 to 50 mol% of Cu content. The long stay behavior of type C suggested that it had implications for degrading type A. To clarify this, polypropylene (PP) film samples containing cuprous oxide were prepared, and their accelerated degradation behavior in seawater was investigated using the advanced oxidation process method using the sulfuric acid radical initiator in seawater of different salinity concentrations. Infrared spectroscopy revealed the formation of a copper soap compound in seawater. Scanning electron microscopy/energy-dispersive X-ray spectroscopy analysis indicated that the chemical reactions between Cl− and cuprous oxide produced Cu+ ions. Changes in the number of polymer chain scissions were investigated at various salinity concentrations of seawater. These findings confirm that Cu+ species promote PP autoxidation.