Weathering and fragmentation of plastic debris in the ocean environment

• Published in: Marine pollution bulletin 2022-07, Vol.180, p.113761-113761, Article 113761
• Main Author: Andrady, Anthony L.
• Format: Article
• Language: English
• Subjects: Fragmentation; Microplastics; Nanoplastics; Seawater; Weathering
• ISSN: 0025-326X; 1879-3363
• DOI: 10.1016/j.marpolbul.2022.113761

Fragmentation of plastic macro-debris into secondary microplastics [MPs] is primarily the result of their extensive oxidation under exposure to solar UV radiation. The heterogeneity in the marine zones with respect to their oxidative potential for plastics, introduces a marked zonal bias in their ability to carry out weathering and fragmentation. Comparing the oxidative environments of the beach zone and the upper pelagic zone with floating plastics, it is argued that the latter tends to preclude photooxidative fragmentation. Abundant MPs found in seawater are therefore more likely to have originated on beaches or land and subsequently transferred to the water, as opposed to being generated by weathering of floating plastic stock. Laboratory-accelerated weathering of plastics in seawater obtains efficient micro-fragmentation and in some instances photo- dissolution of the plastic debris, but these results cannot be reliably extrapolated to natural weathering conditions in the ocean environment. •The oxidative potential of the dry sediment or beach zone is very different from that in the epipelagic zone.•Weathering of floating plastic debris is retarded relative to that on beaches primarily because of the relatively lower oxygen concentrations.•Floating plastic debris is unlikely to weather plastics sufficiently to obtain fragmentation into secondary microplastics (MPs).•The MPs in the water column are therefore more likely to have been originated from pre-weathering of plastic on beaches prior to being introduced into water.