Impact of Conventional vs. Biodegradable and Compostable Microplastics on Eisenia fetida S.: An Ecopathological Approach

: Microplastics represent an emerging issue endangering all ecosystems including soils, where the impact of both conventional and biobased ones remains controversial. The study aimed to assess the effects of two concentrations (1% and 2%) of biodegradable and compostable microplastics and conventional high-density polyethylene microplastics on the abiotic properties of soil, and the ecotoxicological and ecopathological impacts on Eisenia fetida (Savigny, 1826) through histological techniques. Analyses conducted on the evaluation of abiotic soil parameters after 28 days of exposure did not show any significant change compared to the control samples. Ecotoxicological results showed increased mortality and decreased biomass across all treated groups after 14 days of exposure, while a significant reduction in offspring was only observed in 1%-biodegradable and compostable microplastics. Ecopathological analysis revealed inflammatory and/or degenerative phenomena in the epidermal and muscular layers in all treated groups after 14 days of exposure, suggesting the presence of sublethal effects which could impair the well-being of individuals. Overall, our results suggest that the ecopathological approach combined with the classical ecotoxicological one can help explain pathological events which are behind the ecotoxicological endpoints and underline the existence of fine tissue and cell damage even when no changes are observed during ecotoxicological studies.