Effects of Microplastic Pollution on Soil Invertebrate Communities in Agricultural Landscapes of Oyo State, South West Nigeria

Microplastic contamination of agricultural soils is increasingly recognised as a threat to soil ecosystem functioning, yet its effects on soil invertebrate communities in West African farming systems remain almost entirely unexplored. This study investigated the effects of microplastic pollution on soil invertebrate diversity, abundance, and community composition in agricultural landscapes of Oyo State. Soil microplastic concentrations were quantified at thirty agricultural plots spanning a gradient from low to high microplastic loading based on irrigation water source and mulching practice history. Soil invertebrates were extracted using Berlese-Tullgren funnels and hand-sorting of soil cores, and identified to the order level. Structural equation modelling was used to partition direct and indirect effects of microplastic concentration on invertebrate community metrics, accounting for confounding soil physicochemical variables. Results showed significant negative relationships between microplastic concentration and earthworm abundance, with a 58 percent reduction in earthworm density at the highest-contamination plots. Microplastic loading was also negatively associated with total invertebrate taxa richness and functional diversity. Collembolans and mites showed greater tolerance than earthworms to microplastic contamination. Indirect effects of microplastics via soil structure modification, specifically reduced macroporosity, mediated part of the observed invertebrate responses. The study provides the first field-based evidence of microplastic effects on soil invertebrate communities in South West Nigeria and highlights the ecological costs of growing soil microplastic pollution in agricultural landscapes. Keywords: microplastics, soil invertebrates, agricultural soil, Oyo State, ecological effects.