Aged polyethylene microplastics modulate herbicide and antibiotic bioavailability and plant responses: A case study with glyphosate and tetracycline

Microplastics (MPs), increasingly prevalent in agricultural soils, represent an overlooked factor influencing the environmental behavior of xenobiotics and their phytotoxic effects. The present work examines interactions between aged polyethylene microplastics (MP PE), herbicide, and antibiotic under controlled hydroponic conditions using Brassica napus L. as a model plant. It highlights how MP PE influence the bioavailability and toxicity of tetracycline, a glyphosate-based ionic liquid with a surfactant cation, and humic acids. Despite the absence of tissue penetration, MP PE adhered to roots and triggered measurable stress responses, including ∼30 % reductions in chlorophylls and > 20 % decreases in carotenoids, along with shifts in antioxidant enzyme activities - catalase (CAT) reduced by 40 %, ascorbate peroxidase (APx) by 70 %, while peroxidase (POx) increased by 20 %. Co-exposure with herbicide or antibiotic intensified these adverse effects. MP PE demonstrated compound-specific sorption capacity, reducing freely dissolved tetracycline and surfactant cation concentrations by ∼20 %, whereas the glyphosate anion showed marginal affinity. MP PE alone did not significantly alter parameters such as proline content or glutathione S-transferase (GST) activity. While individual xenobiotics exhibited clear toxicity, partial mitigation occurred when sorbed onto MP PE, indicating bioavailability-dependent effects. However, this attenuation was not consistent across endpoints, emphasizing the dual role of MPs as environmental stressors and modulators. Integrating sorption data with physiological and biochemical responses, the results provide evidence that aged microplastics reshape plant exposure to agrochemicals. These findings underscore the need to include MPs in risk assessments to accurately evaluate contaminant behavior and crop health in MP-impacted agroecosystems. • Aged polyethylene MPs alter agrochemical bioavailability in hydroponic systems. • Microplastics act as both stressors and sorption-driven modulators of toxicity. • Sorption to aged PE reduces tetracycline, but not glyphosate bioavailability. • Root-associated microplastics trigger physiological stress without tissue uptake. • Multi-endpoint analysis reveals context-dependent plant responses to MPs.