Microplastics in agricultural soils: Impacts on soil microbial communities, nutrient cycling, earthworm health, and soil ecosystem functions

Global plastic production has increased exponentially since the mid-20th century, leading to the widespread accumulation of microplastics (MPs) in terrestrial ecosystems. Agricultural soils have become major sinks for MPs due to inputs from plastic mulching, sewage sludge, compost, irrigation with reclaimed water, and atmospheric deposition. MPs alter soil physicochemical characteristics, affect nutrient cycling, and disrupt microbial diversity, structure, and enzymatic activities. They also interact with co-occurring pollutants, facilitating the transport and bioavailability of heavy metals and organic contaminants. Earthworms, as key soil engineers, are particularly vulnerable to MP exposure, exhibiting growth inhibition, oxidative stress, intestinal damage, and alterations in gut microbiota composition. Moreover, MPs enhance greenhouse gas emissions by influencing microbial metabolism and soil redox conditions, further impacting ecosystem stability. Human exposure through ingestion, inhalation, and dermal contact raises additional health concerns. This review demonstrates that MPs function as integrated stressors in terrestrial ecosystems, compromising soil health through physicochemical degradation of soil structure, destabilization of microbial communities, and direct toxicity to keystone soil fauna. Impact severity is highly context-dependent, governed by MP properties (size, polymer type), soil characteristics, and exposure duration. Without immediate source control and remediation strategies, continued MP accumulation will irreversibly impair critical soil ecosystem services, threatening agricultural productivity and food security.