This study explores the enhanced retention of small-sized microplastics (MPs) in sand filtration systems using iron-loaded sand (IS). Conventional sand filtration has limited efficiency in removing MPs smaller than the pore size of the filter media, which presents a significant challenge for drinking water treatment plants (DWTPs). To address this issue, quartz sand was modified with iron (hydro)oxide coatings to alter the surface charge, enabling a strong electrostatic attraction with negatively charged MPs. In a 10 mmol/L NaCl solution at a flow rate of 1.5 mL/min, the effluent mass percentages (M