An integrated multimethod approach for size-specific assessment of potentially toxic element adsorption onto micro- and nanoplastics: implications for environmental risk

Micro- and nanoscale plastics (MnPs), arising from the environmental degradation of plastic waste, pose significant environmental and health risks as carriers for potentially toxic element (PTE) metals. This study employs asymmetrical flow field-flow fractionation (AF4) coupled with multi-angle light scattering (MALS) and inductively coupled plasma mass spectrometry (ICP-MS) to provide a size-resolved assessment of chromium (Cr), arsenic (As), and selenium (Se) adsorption onto carboxylated polystyrene nanoparticles (COOH-PSNPs) of 100 nm, 500 nm, and 1000 nm. Cr exhibited the highest adsorption, with adsorption per particle surface area increasing from 9.45 × 10⁻¹⁵ μg nm⁻² for 100 nm particles to 6.87 × 10⁻¹⁴ μg nm⁻² for 1000 nm particles, driven by chemisorptive interactions with carboxyl groups. In contrast, As and Se exhibited slower adsorption rates and significantly weaker interactions, attributed to outer-sphere complexation and electrostatic repulsion. Smaller particles exhibited enhanced adsorption efficiency per unit mass due to their larger surface area-to-volume ratios and higher carboxyl group density (18.5 μEq g⁻¹ for 100 nm compared to 7.9 μEq g⁻¹ for 1000 nm particles). Se adsorption remained negligible across all sizes, near detection limits, highlighting its low affinity for carboxylated surfaces. Our study demonstrates the superior resolution of AF4-MALS-ICP-MS compared to that of bulk ICP-MS, which lacks the ability to discern particle-specific adsorption trends. Unlike bulk ICP-MS, which provides average adsorption values, AF4-MALS-ICP-MS reveals the size-dependent mechanisms influencing metal binding, offering critical insights into the role of MnPs as PTE vectors. The findings highlight the environmental implications of MnPs in facilitating PTE transport and highlights the need for size-specific mitigation strategies. This work sets a foundation for developing more precise risk assessment frameworks and advanced remediation approaches for MnP-contaminated environments.