Plastic debris exposed to coastal marine conditions displays not only the attachment of biofilm, but also a significant mineral deposition on the surface. The presence of mineral deposits and mineral-coated biofilms on the plastic surface yields new hypotheses regarding plastic fate. Metal mineral precipitation on plastic may affect several important factors influencing environmental plastic fate including transport, degradation, and biofilm development. Mineral precipitation influencing plastic mass, and for smaller particles changing aggregation behavior, would in turn influence plastic transport in water and porewater. Furthermore, precipitation could enhance abiotic degradation via processes such as metal catalysis, or form a protective layer shielding the plastics from further degradation. Additionally, community composition may be altered based on the various minerals present on plastics, which could increase the selectivity of microbes on the plastic surface. Here we discuss our current and future work on this topic and present evidence of metal mineral precipitation on plastics from SEM-EDS images of polyethylene and polystyrene exposed for 12 months in situ to the water column and sediments of Svanemøllen Marina, Copenhagen, Denmark. These plastics were further analyzed for mineral characterization using metal extraction with ICP-OES as well as for degradation using FTIR. Enhanced precipitation and degradation was observed on plastics exposed to the more oxygenated water column and upper sediments, indicating the importance of redox conditions and geochemical environment to the metal mineral precipitation process.