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Soils, especially agricultural soils, are thought to be the main reservoir of microplastics in Europe (Lofty et al., 2022). One significant source of MP entering in soils are the plastic mulching on agricultural land. Traditionally, mulches are made of PE, whose particles can contaminate the soil for a long time if the film is not completely removed. Moreover, PE mulches are difficult to recycle because of soil and plant contamination. One alternative is the development and the use of biodegradable mulches. These are designed to be buried with plant residues at the end of the crop. According to the current standard (EN 17033), after two years in the soil, the films should be 90% biodegraded. However, questions remain about their accumulation and their potential impacts on soil life or food. The BIOMALEG project aims to assess the microplastic contamination of agricultural soils that have been cultivated under mulch for one or twenty years. As some mulches are biodegradables, the extraction methods of microplastics must be adapted to this polymer type. In addition, squash crops will be used to assess the potential entry of plastic particles into the food. Particles from mulches are found on the pumpkin peel. Also see: https://micro2022.sciencesconf.org/425940/document, In MICRO 2022, Online Atlas Edition: Plastic Pollution from MACRO to nano

The latest literature suggests that organic fertilizers are one of the first sources of contamination of agricultural soils. Indeed, organic materials for intended soil amendments (e.g. composts, green waste, manure, sewage sludge) are the result of various processes and can be contaminated by microplastics (MP), such as packaging residues. In order to improve our knowledge on the level of contamination, as well as on the nature of MP in organic amendments, the PRO project (2021-2023) has been set up by Ademe (French Agency for Ecological Transition). This project has several challenges: to identify the matrices acting as sources of MP, to study the diversity and origins of these MP, and to estimate the potential flows to agricultural land. Within this framework, the IRDL (Institut de Recherche Dupuy de Lôme) is responsible for setting up and testing the method for extracting and analysing MP contaminating these matrices. Our mission is to validate a digestion protocol applicable to 21 complex solid matrices rich in organic matter while, at the same time, ensuring the integrity of extracted polymers (especially biodegradable ones). 83 samples are planned for this project, and half have already been analysed. Preliminary recommendations following these tests and unpublished results will be presented. Also see: https://micro2022.sciencesconf.org/427005/document, In MICRO 2022, Online Atlas Edition: Plastic Pollution from MACRO to nano

Among actual bioplastics, polyhydroxyalkanoates (PHA) has raised great interest as a substitute to persistent petroleum based plastic materials. Naturally produced by numerous bacteria as a form of carbon storage, PHA show good signs of biodegradability in natural ecosystems. Here, we evaluate the influence of the chemical structure (eight formulations of short and medium-chain-length PHA) on the biodegradability of PHA in the marine environment. We used an original miniaturized experimental design that allowed transdisciplinary analyses (dissolved inorganic carbon production, oxygen consumption, heterotrophic bacterial activity, microbial biomass and diversity, molecular weight, production of oligomers and monomers). After 30 days of incubation with a natural community, we observed different signs of biodegradability for the eight PHA. In particular, higher microbial activity was monitored in short-chain-length (scl) sample than in medium-chain-length (mcl). To better understand scl-PHA biodegradation by marine microbes, radio-labeled 13C-PHB was incubated with natural communities for 90 days. Microbial activity and biomass were monitored, and DNA was extracted on days 5, 13, 30 and 90 of incubation. DNA-Stable isotope probing (DNA-SIP) was used in order to describe degrading and opportunist communities. Metabarcoding analyses highlighted taxonomic differences between 13C and 12C fractions, and metagenomic analyses allowed us to decipher the functional difference between the two fractions. Also see: https://micro2022.sciencesconf.org/427467/document, In MICRO 2022, Online Atlas Edition: Plastic Pollution from MACRO to nano

Polyhydroxyalkanoates (PHA) are polyesters derived from bacterial cultures (biosourced). They offer a diverse range of chemical structures with remarkable functional properties . Moreover, some of them have already demonstrated much greater biodegradation capacities than conventional polymers although the molecular mechanisms involved in their biodegradation in the marine environment are still little studied. Our work on the biosynthesis of custom PHA from different bacterial strains and different carbon sources has made it possible to produce 6 short-chain (scl) and medium-chain (mcl) PHA by fermentation process. We then carried out biodegradability tests of these PHA in the marine environment, approaching natural marine conditions. The microbial inoculum used for these tests was the biofilm that naturally colonized PHA films incubated in natural seawater for one month. Biodegradability was followed in artificial seawater during three months with PHA as the sole carbon source by several complementary methods: consumption of oxygen, bacterial production, ATP and microscopy. Evolution of microbial communities were studied along the three-months experiment on each PHA by 16S rDNA gene sequencing. Our results confirm the microbial activities on all PHA and the biodegradability of certain PHA in the marine environment. For example, consumption of oxygen was 2 to 40 times greater for PHA than for polyethylene while cellulose was 24 times greater than this same petrochemical polymer. It demonstrates that the type of PHA have a significant impact on their biodegradation kinetics. A better knowledge of the role of the structure of PHA, their properties and the bacterial mechanisms involved in their biodegradation will allow the development of "tailor-made" PHA adapted to biodegradation in the marine environment. Also see: https://micro2022.sciencesconf.org/427017/document, In MICRO 2022, Online Atlas Edition: Plastic Pollution from MACRO to nano