Ecotoxicological Effects of Commercial Microplastics on Earthworm Eisenia fetida (Savigny, 1826) (Clitellata; Lumbricidae)

As soil invertebrates with a unique digestive system, earthworms are regularly used as bioindicators and test organisms. Due to their burrowing activity and casting, earthworms are involved in the structuring of the soil. However, this way of life exposes them to different pollutants, including microplastic particles. Although the use of plastics is economically justified, it has a major impact on living organisms. In this study, the influence of different concentrations (2.5%, 5%, and 7% (w/w)) of commercial glitter as a primary source of microplastics (MPs) on mortality, growth, cocoon production, avoidance behavior, and bioaccumulation ability during a four-week exposure of the earthworm species Eisenia fetida was investigated. The mortality was higher at 5% and 7% MPs in the soil than at 2.5% and in the control (0%) after 28 days, and the number of cocoons and growth rate decreased with an increasing MP concentration. However, the earthworms did not avoid the soil with MPs. Furthermore, the dissection of the digestive system enabled the identification of MP distribution. The sections of the digestive system were additionally examined under a fluorescence microscope. The results indicated that non-selective feeding enabled the input of MPs into the earthworm's body and, thus, into food webs.