New versus naturally aged greenhouse cover films: Degradation and micro-nanoplastics characterization under sunlight exposure.

The understanding of microplastic degradation and its effects remains limited due to the absence of accurate analytical techniques for detecting and quantifying micro- and nanoplastics. In this study, we investigated the release of nanoplastics and small microplastics in water from low-density polyethylene (LDPE) greenhouse cover films under simulated sunlight exposure for six months. Our analysis included both new and naturally aged (used) cover films, enabling us to evaluate the impact of natural aging. Additionally, photooxidation effects were assessed by comparing irradiated and non-irradiated conditions. Scanning electron microscopy (SEM) and nanoparticle tracking analysis (NTA) confirmed the presence of particles below 1 µm in both irradiated and non-irradiated cover films. NTA revealed a clear effect of natural aging, with used films releasing more particles than new films but no impact of photooxidation, as irradiated and non-irradiated cover films released similar amounts of particles at each time point. Raman spectroscopy demonstrated the lower crystallinity of the released PE nanoplastics compared to the new films. Flow cytometry and total organic carbon data provided evidence of the release of additional material besides PE, and a clear effect of both simulated and natural aging, with photodegradation effects observed only for the new cover films. Finally, our results underscore the importance of studying the aging processes in both new and used plastic products using complementary techniques to assess the environmental fate and safety risks posed by plastics used in agriculture.

Ageing and fragmentation of marine microplastics.

The generation of small fragments from the environmental ageing of microplastics (MPs) is still a poorly known process. This work addresses the fragmentation of MPs obtained from marine debris consisting of polyethylene and polypropylene (PE and PP in environmental mixture) and polystyrene (PS) after exposure to accelerated ageing by irradiation and mechanical stirring. Number particle size distribution in the 1-100 µm range was assessed by combining laser diffractometry with particle counts from flow cytometry. The results showed the generation of a high number of small MP particles, which reached 105-106 items/mg of plastic with most fragments <2 µm. The results showed that environmentally aged MPs give rise to a larger number of small MPs in a pattern consistent with progressive fragmentation in the three spatial dimensions. The proportion of small MPs was much higher than that found in current sampling campaigns, suggesting a severe underestimation of the environmental presence of small MPs. We also demonstrated the generation of nanoplastics (NPs) in the fraction <1 µm from irradiated runs. The results showed that the mechanism that produced nanoplastics (NPs) from MPs was irradiation, which yielded up to 1011-1013 NPs/g with particle size in the few hundreds of nm range. Our results are relevant for the assessment of fate and risk of plastic debris in the environment showing that the number of small plastic fragments produced during the ageing of MPs is much larger than expect from the extrapolation of larger size populations.

Generation of nanoplastics during the photoageing of low-density polyethylene.

In this work, we studied the hydrolytic and photochemical degradation of three low-density polyethylene (LDPE) materials, within the size range of microplastics (MP). The MPs were exposed to mechanical agitation and UV irradiation equivalent to one year of solar UVB + UVA in a stirred photoreactor. Flow cytometry was used to track the formation of small (1-25 µm) MPs by applying Mie's theory to derive the size of MP particles from scattering intensity readings. The calculation was based on a calibration with polystyrene (PS) beads. The results showed that the generation of 1-5 µm MP reached 104-105 MPs in the 1-25 µm range per gram of LDPE. ATR-FTIR and micro-FTIR measurements evidenced the formation of oxygenated moieties, namely hydroxyl, carbonyl, and carbon-oxygen bonds, which increased with irradiation time. We also found evidence of the production of a high number of nanoplastics (<1 µm, NPs). The Dynamic Light Scattering size of secondary NPs was in the hundreds of nm range and might represent up to 1010 NPs per gram of LDPE. Our results allowed the unambiguous spectroscopic assessment of the generation of NPs from LDPE under conditions simulating environmental exposure to UV irradiation and used flow cytometry for the first-time to track the formation of secondary MPs.