BIOdegradable MICroplastics effects on fish MICrobiota – BIOMIC

Occurrence of microplastics (MPs) is documented in all terrestrial and aquatic environments at ever growing concentrations. Ingestion of MPs by fish has been massively reported whatever their ecological traits and living habitat. Long-term chronic exposures of marine organisms to MPs was shown to elicit physiological disruptions with consequences on life history traits (decrease in growth and reproduction), which may contribute to the endangerment of wild populations. Energy budget unbalance was suggested to contribute to these physiological disruptions but underlying mechanisms are not clearly identified. Further, gut microbiota is involved in many biological processes and its disruption upon exposure to MPs has been demonstrated (dysbiosis). It may be one of the pathways, additional to energy budget unbalance, leading to physiological effects. In addition, despite the fact that morphology of gastrointestinal tract appears to be unaffected by exposure to MPs, its protective and assimilation functions may be affected by exposure to MPs, as shown for example by changes in mucus abundance. These last disruptions may also contribute to metabolism and/or energy balance defects.
Several initiatives emerged to mitigate emission of MPs and their effects on ecosystems. Among them are biodegradable polymers. Biodegradation is a complex process including several steps which require specific environmental conditions. Misuse or mismanagement of biodegradable items may result in biodegradable MPs (bMPs) ending in the marine environments. Biodegradation in nature also requires time (months to years) therefore release in the aquatic environment of biodegradable items supposed to be degraded (e.g. personal care products microbeads) may also contribute to high levels of bMPs. Very little is known about the toxicity of bMPs, especially when considering environmentally relevant exposure conditions. They may exert toxicity as conventional MPs do but their biodegradation properties may elicit specific modes of action toward organisms ingesting them and/or gut microbiota. It is then of utmost importance to evaluate their toxicity.
In this context, the objectives of BIOMIC are to characterise the toxicity of two bMPs (PLA and PHBV) vs. a conventional MPs (PS) after chronic exposure of fish at environmentally relevant concentrations. Investigations will cover both individual and molecular levels to reveal defects concerning life history traits (growth, reproduction and behaviour) and energy balance (elementary analyses and metabolism genes expression). Over this long–term exposure, samples will be taken after 2-3 and 4-6 months of exposure to evaluate changes in intestinal microbiota (16S sequencing and metabolites) and intestinal function, including barrier function (e.g. mucus, histology). Attention will be paid to microbiota changes which may be polymer-specific. Finally, BIOMIC will evaluate if interactions of bMPs with organisms (gastrointestinal digestion process) and microbiota action influence erosion and fragmentation of bMPs which may in turn increases bMPs concentration and effects (e.g. using atomic force microscopy, size exclusion chromatography).
Beyond increasing scientific knowledge, BIOMIC and its multidisciplinary consortium will be a valuable relay toward society, policy makers and stakeholders to raise awareness on the potential issues related with biodegradable plastic items.