Surface-charge-dependent ovarian toxicity of polystyrene microplastics: Insights into accumulation, mitochondrial damage, and macrophage polarization.

The aging of microplastics (MPs) in the environment can result in microplastic particles with different functional groups, yet the impact of these modifications on ovarian function and damage remains poorly understood. This study investigated the accumulation and toxicity of polystyrene microplastics (PS-MPs), some carrying different functional groups (PS-NH₂, PS, PS-COOH), in the rat ovary following oral exposure. Our results demonstrated that different surface functional groups significantly affected MPs accumulation in the ovary, in this order: PS-NH₂ > PS > PS-COOH. Exposure to MPs, especially PS-NH₂, disrupted sex hormone balance, increased oxidative stress, and induced mitochondrial damage. Furthermore, all MPs increased macrophage infiltration and iron accumulation, promoting ferroptosis in ovarian cells. Notably, negatively charged PS-COOH MPs skewed macrophage polarization toward the pro-inflammatory M1 phenotype, which increased oxidative stress and ovarian damage. These findings reveal that surface functionalization and charge play a critical role in MP-induced ovarian toxicity, providing new insights into the mechanisms underlying reproductive health risks, and for developing intervention strategies to reduce environmental MPs exposure harm.