First-time evaluation of 137Cs adsorption onto virgin PLA, PET, and PVC microplastics

• First comprehensive investigation of 137Cs adsorption onto PLA, PET, and PVC virgin microplastics (MPs). • Cs⁺ adsorption is strongly influenced by solution pH, with PLA showing maximum uptake at pH 8. • Adsorption kinetics follow pseudo second order models, confirming chemisorption dominance on all MPs. • PLA and PET exhibit multilayer adsorption (Freundlich), while PVC shows Langmuir monolayer adsorption with 10.28 mg/g capacity. • Competitive ion studies reveal ion-bridging enhances Cs⁺ adsorption on PVC, affecting environmental transport behaviour. This study presents the first investigation into the adsorption behaviours of polylactic acid (PLA), polyethylene terephthalate (PET), and polyvinyl chloride (PVC) virgin microplastics (MPs) for cesium-137 ( 137 Cs) from aqueous solutions. The MPs were characterized using field-emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and pHpzc analysis. The effects of various parameters, including solution pH, contact time, Cs⁺ concentration, adsorbent dosage, temperature, and the presence of matrix ions, were examined. The adsorption study results indicate that adsorption capacity is strongly influenced by pH. PLA shows enhanced uptake under alkaline conditions (maximum: 29.0 µg/g at pH 8), PET favors acidic conditions, while PVC shows different behavior with peak adsorption at pH 4. Kinetic analysis revealed that Cs⁺ adsorption follows a pseudo-second-order model, indicating chemisorption dominance, which was further confirmed by FT-IR and XPS analyses, with PLA achieving the fastest and highest uptake (∼39 µg/g) due to abundant functional groups. Isotherm modelling revealed multilayer adsorption on PLA and PET (Freundlich model) and monolayer adsorption on PVC (Langmuir model), with the latter exhibiting the highest theoretical capacity of 10.28 mg/g. Adsorbent dosage inversely affected adsorption capacity, while thermodynamic studies confirmed the process is spontaneous, endothermic, and entropy-driven. Under competitive cation conditions, PVC demonstrated a pronounced increase in Cs + uptake possibly due to the ion-bridging due to steric or functional group constraints. These findings elucidate microplastic interactions with Cs + , providing valuable insights for environmental risk assessment and adsorption behaviour of the PLA, PET and PVC MPs for the transport of Cs + in the environment.