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Tetracycline uptake by photoaged polypropylene and high-density polyethylene microplastics in water
Summary
Sunlight exposure makes certain plastics—especially polypropylene (found in items like bottle caps and food containers)—much better at soaking up tetracycline, a common antibiotic, from water. This matters because it means sun-weathered microplastics floating in rivers and oceans could act like tiny sponges that collect and transport antibiotics, potentially spreading them (and contributing to antibiotic resistance) as these particles move through waterways, get eaten by fish, or make their way into our food and water supply.
Microplastics coexist with various contaminants in aquatic environments and may serve as critical sorbents for those contaminants, including tetracycline (TC) antibiotics.In this study, the adsorption behavior of TC on pristine and photoaged polypropylene (PP) and high-density polyethylene (HDPE) microplastics was systematically investigated in aqueous systems.Fourier-transform infrared spectroscopy and scanning electron microscopy were used to observe the structural and surface changes induced by photoaging process.Batch adsorption experiments were conducted to study the effects of contact time, solution pH, and initial TC concentration.Photoaging significantly enhanced TC uptake on both type of polymers, with PP exhibiting a higher adsorption capacity than HDPE.Adsorption on both polymers followed pseudo-second-order kinetics, with photoaged materials exhibited lower rate constants but higher equilibrium capacities.The Langmuir model provided the best fit to equilibrium data, indicating the monolayer coverage of TC on polymer surfaces.The estimated maximum adsorption capacity (Qₘₐₓ) of PP increased by more than twofold following photoaging, rising from 4.15 mg g⁻¹ to 9.22 mg g⁻¹, whereas HDPE exhibited consistently low capacities (1.59-1.60 mg g⁻¹) regardless of aging.These results demonstrate that polymer type and environmental aging critically govern the role of microplastics as antibiotic carriers in aquatic environments.