Ecotoxicological Effects of Microplastics in Agricultural Soil Emerge With Increasing Test System Complexity

The aim of this thesis was to provide insight into the hazards of a number of mulching film-based MPs in agricultural soils, by determining their toxicity to Collembola. Collembola were used as a representative of the soil ecosystem, which were tested both as a single species, as well as in an integrated approach by using mesocosms, in which they were assessed as part of the system as a whole. Collembola, or springtails, are a class of soil arthropods that play an important role in soil nutrient cycling and can be found in large numbers in soils around the world. By assessing the toxicity of mulching film-based MPs to Collembola in agricultural soil, I set out the following objectives: 1) To assess the short-term ecotoxicological effects of mulching film-based MPs on Collembola. 2) To determine the multigenerational effects of mulching film-based MPs on Collembola. 3) To assess the effects of mulching film-based MPs on Collembola community composition. 4) To provide insights into the effects of mulching film-based MPs on the soil ecosystem. 5) To provide effect-based insights into the possible exacerbated toxicity to Collembola of other chemical compounds in co-exposure to MPs. This thesis demonstrates that while mulching film-derived MPs generally show little effect in single species tests, they may influence soil physicochemical properties and ecosystem functioning at environmentally relevant concentrations. It emphasizes the multifaceted effects of MPs and the importance of assessing these effects on more complex test systems with higher levels of biological organisation and ecological relevance. The added value of using more ecologically relevant test systems is further highlighted by the strong interactions observed between MPs and chemicals co-occurring in the soil. In conclusion, this thesis provides new insights into the ecological effects of MPs, the different mechanisms through which they may effect soil ecosystems, and the necessity to use environmentally relevant test systems for the risk assessment of MPs in soil.