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Size-dependent long-term weathering converting floating polypropylene macro- and microplastics into nanoplastics in coastal seawater environments
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Researchers found that floating polypropylene plastics of different sizes undergo long-term weathering in coastal seawater, with particle size decreasing by over 99% after accelerated UV exposure, demonstrating a size-dependent pathway for converting macroplastics into nanoplastics.
In this study, we systematically developed the long-term photoaging behavior of different-sized polypropylene (PP) floating plastic wastes in a coastal seawater environment. After 68 d of laboratory accelerated UV irradiation, the PP plastic particle size decreased by 99.3 ± 0.15%, and nanoplastics (average size: 435 ± 250 nm) were produced with a maximum yield of 57.9%, evidencing that natural sunlight irradiation-induced long-term photoaging ultimately converts floating plastic waste in marine environments into micro- and nanoplastics. Subsequently, when comparing the photoaging rate of different sized PP plastics in coastal seawater, we discovered that large sized PP plastics (1000-2000 and 5000-7000 μm) showed a lower photoaging rate than that of small sized PP plastic debris (0-150 and 300-500 μm), with the decrease rate of plastic crystallinity as follow: 0-150 μm (2.01 d) > 300-500 μm (1.25 d) > 1000-2000 μm (0.780 d) and 5000-7000 μm (0.900 d). This result can be attributed to the small size PP plastics producing more reactive oxygen species (ROS) species, with the formation capacity of hydroxyl radical •OH as follows: 0-150 μm (6.46 × 10 M) > 300-500 μm (4.87 × 10 M) > 500-1000 (3.61 × 10 M) and 5000-7000 μm (3.73 × 10 M). The findings obtained in this study offer a new perspective on the formation and ecological risks of PP nanoplastics in current coastal seawater environments.
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Researchers studied how UV exposure duration and mechanical abrasion combine to fragment different plastic types under simulated beach conditions. They found that polypropylene was far more susceptible to fragmentation than polyethylene after UV weathering, while expanded polystyrene broke apart readily even without UV exposure. The experiments showed that a large fraction of fragmented particles were too small to recover, suggesting that significant amounts of nanoplastic are being generated on beaches.
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Researchers simulated UV weathering of polypropylene plastic and tracked how exposure progressively degraded the polymer, causing surface cracking and changes in mechanical properties that facilitate breakdown into microplastics. The results help explain how environmental weathering of plastic waste accelerates microplastic formation.
Microplastic particle versus fiber generation during photo-transformation in simulated seawater
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Researchers exposed common plastic films and fibers to simulated sunlight in seawater and tracked the photo-transformation process, finding that particles and fibers formed at different rates and that UV irradiation preferentially generates certain morphologies depending on the parent polymer.
Contrasting SizeDependence of Photochemical Lifetimesof Polypropylene and Expanded Polystyrene Microplastics in SurfaceWaters
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Researchers found that photochemical dissolution of polypropylene and expanded polystyrene microplastics in surface waters does not scale linearly with surface-area-to-volume ratio as particle size decreases. Instead, the two polymers show contrasting size-dependent photochemical lifetimes, suggesting particle size and polymer type must both be considered when modeling plastic persistence in aquatic environments.
Contrasting SizeDependence of Photochemical Lifetimesof Polypropylene and Expanded Polystyrene Microplastics in SurfaceWaters
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Researchers found that photochemical dissolution of polypropylene and expanded polystyrene microplastics in surface waters does not scale linearly with surface-area-to-volume ratio as particle size decreases. Instead, the two polymers show contrasting size-dependent photochemical lifetimes, suggesting particle size and polymer type must both be considered when modeling plastic persistence in aquatic environments.
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When a large batch of papers lands in the Atlas, we read through it and send a short write-up of what stood out.