Superoxide (O2-), generated by mitochondrial respiration and redox enzymes, may act as a cellular ageing trigger (CAT) when dysregulated. This study investigated whether mitochondrial (rotenone-induced) and cytoplasmic (paraquat-induced) O2- imbalance produces similar or distinct oxi-inflammatory activation in human peripheral blood mononuclear cells (PBMCs). Two in vitro protocols were performed. First, PBMCs were exposed to rotenone (ROT) or paraquat (PQT) for 6 or 24 h, using phytohaemagglutinin (PHA) as a positive control. Second, 48-h cultures from 21 donors, including healthy controls (HC) and individuals with Parkinson's disease (PD), were treated with 30 μM ROT or PQT. Cell viability was evaluated by the MTT assay (metabolic activity) and trypan blue exclusion (membrane integrity). Cytokines, O2-, nitric oxide (NO) and morphometric parameters were quantified. ROT and PQT induced distinct early responses: ROT increased IL-1β and NO, whereas PQT caused delayed elevations of IL-1β, O2- and NO. Because no baseline differences were detected between HC and PD donors, data were analysed jointly. After 48 h, both oxidants elevated IL-1β, IL-6, TNF-α and NO. Morphometric analysis revealed ROT-associated fragmentation and PQT-induced hyperchromatic aggregates, consistent with pro-inflammatory damage-associated molecular patterns (DAMPs). These findings indicate that mitochondrial and cytoplasmic O2- imbalance initiates oxi-inflammatory activation in PBMCs, supporting superoxide dysregulation as a potential CAT and a hormetic modulator of ageing-related signalling.