Chemical contaminant vectorization by microplastics during food waste recycling: the case study of insect-based bioconversion – VECTOR

Microplastics are ubiquitous in the environment, giving rise to major concern because of their various adverse effects on living organisms, including humans. Indeed, microplastics have the capacity to vector various harmful adsorbed chemical contaminants, whether additives introduced during plastics manufacturing or environmental pollutants. This problem is of particular concern because, in the context of food circular economy models, there is a serious lack of knowledge about the transfer and the entry into the food chain of microplastics and vectorized chemical contaminants. Among circular economy models, the industrial recycling of biowaste by black soldier fly larvae (Hermetia illucens) has emerged as a relevant solution in recent years to complement composting and anaerobic digestion since this process makes it possible to produce both larvae for animal feed and fertilizers, from the larval excrement, called frass. The aim of VECTOR project will therefore be to compare the flows of microplastics from petroleum-derived plastics and bioplastics and of the chemical contaminants they vectorize in a food waste recycling chain, using the case study of insect-based bioconversion by black soldier fly larvae. Heavy metals, as an example of an environmental pollutant, and phthalates, as an example of a plastic additive, will be addressed in the project. A benchmarking of different analytical chemistry and imaging techniques will first be carried out, in order to identify the most reliable and robust combination of methods for characterizing microplastics and quantifying the chemical contaminants adsorbed on these microplastics. Based on these methodological developments, the second step will be to assess the transfers of microplastics and vectorized heavy metals during insect-based bioconversion, from food waste streams to black soldier fly larvae and frass. A kinetic model will then be developed to estimate the microplastic and heavy metal content of larvae as a function of the initial contamination of their food substrate. An in vitro digestion protocol simulating the digestive tract of larvae in a simplified manner will also be implemented in a third step to investigate the modulating factors of these transfers. These factors could be of interest in limiting, or even preventing, the release of chemical contaminants vectorized by microplastics into the bioaccessible fraction likely to cross the intestinal barrier. Finally, preliminary data will be obtained to compare the impact of insect-based bioconversion with two other biowaste recycling approaches, composting and anaerobic digestion, on the potential introduction into the food chain of microplastics and vectorized chemical contaminants via end-products (fertilizers and larvae). The study of bioplastics is an integral part of this project, given the anticipated increase in their production over the coming years. It is crucial to assess their capacity to vectorize chemical contaminants, as well as their fate and degradation (complete or incomplete) during biowaste recycling processes. Ultimately, the VECTOR project will provide critical new data for better assessment of the chemical risks associated with microplastics.