Hepatotoxicity of Styrene-acrylonitrile Microplastics in Mice: Size-Dependent Effects on Liver Function, Oxidative Stress and Histopathology

Abstract

Microplastic pollution poses environmental and public health risks, yet the hepatotoxicity of styrene-acrylonitrile (SAN) copolymers remains understudied relative to polystyrene and polyethylene. This study evaluated the hepatotoxicity of SAN microplastics in male mice. SAN-MPs isolated from commercial takeaway food containers were characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX), and fractionated into ≤150, ≤300 and ≤400 µm particles. Ninety-five male mice (6 weeks old; 36.2 g) were randomized into 19 groups (n = 5). Treatment mice received once-daily oral gavage of SAN-MP suspensions (1 mg/5 mL Milli-Q water, ultrasonicated before administration) at progressively escalating doses (0.2–1.0 mL/kg) over 42 days; controls received an equal volume of vehicle. Hepatotoxicity was assessed by serum liver function markers, hepatic oxidative stress indices (MDA, GSH, catalase) and H&E histopathology. Exposure induced significant time-dependent elevations in ALT, AST and total bilirubin, with the ≤300 µm fraction producing the most pronounced biochemical perturbations; albumin increased at later time points while total protein remained unchanged. Oxidative stress responses were size-specific: hepatic GSH was significantly elevated in the ≤300 µm group at days 28 and 42, whereas catalase activity was suppressed in the ≤400 µm and ≤150 µm groups at terminal time points. Histopathological injury progressed from periportal inflammation and sinusoidal congestion (day 7) to widespread necrosis and architectural disorganization (day 42), with the ≤300 µm and ≤400 µm groups exhibiting more severe lesions. These findings demonstrate size-dependent SAN-MP hepatotoxicity and highlight the need for polymer-specific risk assessment of food-contact plastics.