Styrene-acrylonitrile Microplastics Alters Renal Redox Homeostasis and Induce Inflammatory Histopathology in Mice in a Particle Size-Dependent Manner

Abstract

Styrene-acrylonitrile (SAN) copolymers are employed in disposable food-packaging materials, yet the nephrotoxic potential of the microplastics remains poorly characterised. This study investigated the particle size-dependent renal toxicity of SAN microplastics in mice following oral exposure. SAN-MPs were mechanically fragmented from commercial takeaway containers into ≤150, ≤300 and ≤400 μm fractions. Ninety-five adult male mice were allocated to control and three treatment groups, exposed via oral gavage to doses over 42 days. Renal function was examined by serum creatinine, urea and sodium. Oxidative stress was determined by malondialdehyde, reduced glutathione and catalase. Histopathological alterations were also examined by H&E staining. SEM revealed irregular, flaky particles, while EDS confirmed carbon and nitrogen profiles with aluminium and trace contaminants. Serum creatinine and urea trended upward as the ≤300 μm group showed significantly elevated urea at Day 21. MDA was significantly increased in the ≤150 μm group at Days 14 and 28 and in the ≤300 μm group at Day 42. GSH and CAT showed early responses followed by exhaustion. Histopathology revealed progressive inflammatory infiltration and collagen deposition, with the ≤300 μm fraction causing the earliest and most severe damage. These findings show that SAN-MPs induce particle size- and time-dependent nephrotoxicity with the ≤300 μm fraction having the greatest pathological risk. Oxidative stress and inflammatory injury represent central mechanisms that underscore the need for toxicological scrutiny of SAN-containing food-contact plastics.