Microplastics and Early Plant Development: A Critical Review of Exposure-Dependent Effects, Inhibitory Mechanisms, and Mitigation Strategies

Microplastics (MPs) are emerging environmental stressors in terrestrial ecosystems, yet their effects on early plant development remain incompletely understood. This critical review synthesized evidence from 39 peer-reviewed experimental studies published between January 2019 and June 2026 on seed germination and early seedling growth. The synthesis considered polymer type, particle size, exposure concentration and duration, plant species, growth medium, uptake pathways, inhibitory mechanisms, and mitigation strategies. The findings indicate that Polystyrene (PS) was the most frequently reported polymer, followed by Polyethylene (PE) and Polyethylene Terephthalate (PET), with MP particle sizes ranging from 0.08 μm to 3 mm. Phytotoxicity was jointly influenced by polymer properties, exposure concentration, exposure duration, plant traits, and growth medium. Particle size emerged as an important physicochemical characteristic influencing the mechanisms underlying MP phytotoxicity. Increasing exposure concentrations generally intensified phytotoxic responses, with morphological traits consistently declining at higher MP concentrations. Physiological responses, particularly antioxidant defenses, were initially activated but declined when stress exceeded the plant’s capacity, resulting in oxidative damage and growth inhibition. Rice and wheat were among the most frequently investigated crops and generally exhibited inhibitory responses across several early growth endpoints. Mechanistically, MPs may restrict water and nutrient uptake, enter roots through cracks and intercellular spaces, and induce oxidative stress, cytotoxicity, and genotoxicity. The review highlights several potential mitigation approaches, including improved soil management, reduced agricultural plastic use, material substitution, microbial degradation, and the application of exogenous antioxidants.