Assessing the role of short-chain chlorinated paraffins in the toxicity of ambient particulate matter

Short-chain chlorinated paraffins (SCCPs) are widespread in atmospheric particulate matter (PM), but their toxicological contribution when adsorbed onto PM remains unclear. Using a respiratory A549/THP-1 co-culture cell model, we evaluated the effects of low-dose SCCPs (based on levels in real environment) combined with carbon particles (60 nm). Carbon particles significantly impaired cellular metabolic activity and induced oxidative stress, whereas SCCPs alone at low doses had minimal cytotoxic or oxidative effects. Co-exposure to SCCPs and carbon particles did not consistently exacerbate toxicity compared to carbon particles alone, and in some cases, even attenuated specific effects. Inflammatory cytokine expression revealed a general dose-dependent suppression, particularly in co-exposure groups, with IL-8 and TNF-α levels significantly reduced. Cell cycle alterations were minor across all groups, though subtle shifts in DNA replication phases were observed. Toxic potency evaluation showed that carbon particles combined with high-dose SCCPs (Maoming-equivalent) had slightly greater overall toxicity (0.228) than carbon particles alone (0.220) or low-dose SCCPs (Guangzhou-equivalent, 0.211), indicating a potential threshold effect for SCCP contribution at low environmental levels. This study highlights the complex and non-linear interactions between SCCPs and PM in terms of cellular toxicity and emphasizes the importance of considering environmentally relevant co-exposure scenarios in health risk assessments.