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Artificial weathering of plastics used in oyster farming
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Researchers studied the weathering of polypropylene oyster spat collectors after approximately 15 years of use in marine environments, finding extensive physical, chemical, and mechanical degradation that produces large quantities of plastic fragments and microplastics, making oyster aquaculture a significant source of coastal plastic pollution.
With the omnipresence of plastic litter from oyster farming in marine coastal areas, the objective of this work was to better understand the weathering of plastics used in this field, focusing on oyster spat collectors. During their use, around fifteen years, collectors made of polypropylene (PP) undergo numerous degradations, alternatively submerged, emerged in seawater, and stored outdoor until the next cycle. They weaken, crack, break, end up fragmenting and disseminated in the environment as microplastics associated to persistent organic pollutants. In this work, a comparison of 55 months of in situ weathering with five months of artificial weathering in air or in artificial seawater in a homemade UV chamber was conducted to better understand the mechanisms involved. Chemical, thermal and surface characterizations of virgin and weathered samples were conducted using Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC) and Environmental Scanning Electron Microscopy (ESEM). After 55 months of in situ weathering, collectors were notably damaged with large fissures and loss of microplastics (MPs) associated with an increase of carbonyl index values and a decrease of melting temperatures and crystallinity rates. Considering only UV irradiation, five months of artificial weathering at 30 °C under continuous irradiation of 6.9 W/m under UV lamps (295-400 nm) reproduced approximately 4.4 months of natural sunlight. Artificial weathering confirmed that photooxidation by combined effects of UV rays and oxygen was the main weathering mechanism and was reduced in seawater. These results help to understand the mechanisms involved in the weathering of these collectors in the marine environment and provide valuable information for industrials and professionals. Our study suggests a better storage away from UV rays and a reduction of the duration of use compared to current practices.
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Researchers exposed Pacific oyster (Crassostrea gigas) larvae and spat to microplastics derived from weathered aquaculture materials and found that both settlement rates and spat growth were significantly reduced, raising concerns about plastic pollution in aquaculture operations.
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Field experiments in Chesapeake Bay tracked how macroplastic items of different polymer types weathered and fragmented over time in a coastal environment. The study found that UV exposure and wave action caused rapid surface degradation and fragmentation, with important implications for how quickly plastic pollution generates secondary microplastics in coastal zones.
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Laboratory weathering experiments showed that common plastic items (HDPE, LDPE, PP, PS, PC) retain their bulk structural integrity even after simulated UV and mechanical exposure equivalent to decades of coastal conditions, yet shed a thin surface layer rich in microplastic fragments. This means macroplastics in the ocean act as a persistent, long-term source of microplastic particles even when they appear physically intact.
Influence of weathering on the microplastics formation in the environment
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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.
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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.