Non-targeted screening and toxicity assessment of nitrophenols in atmospheric particulate matter using high-resolution mass spectrometry

Nitrophenols (NPs), as key toxic components in atmospheric fine particulate matter, exhibit poorly understood coupling mechanisms between environmental behaviors and toxicological risks. This study established an integrated research framework from molecular identification to toxicity assessment, combining high-time-resolution online sampling systems with high-resolution mass spectrometry (both non-targeted and targeted analyses) and computational toxicology approaches. Non-targeted spectrometry analysis of Shanghai PM2.5 during summer 2023 revealed that NPs accounted for 25% of aromatic compounds, with quantified concentrations of 10 NPs ranging from 0.02 to 6.46 ng/m³. Monocyclic NPs showed 1–2 orders of magnitude higher abundance than polycyclic/heterocyclic derivatives. Time-series analysis demonstrated significant clustering patterns among NPs, where outlier NP pairs (e.g., 4H4NBP/4NP) exhibited distinct structure-activity relationships: π-conjugation effects, nitro-substitution, and hydrophobic moieties collectively regulated cellular toxicity (IC₅₀). Notably, these structure-activity-governed NP pairs displayed dynamic environmental responsiveness (to NO₂ concentration and relative humidity) primarily driven by dose-response effect. The composite toxicity analysis demonstrated more than 50% reduction in combined toxicity compared to individual components, with high-concentration species (e.g., 4NP, 4NmC) substantially attenuating toxic contributions from low-concentration structural analogs (4H4NBP, 5N2MP). However, when structural differences reached critical thresholds (e.g., 5N2MP exhibiting one order of magnitude lower toxicity threshold than 4NmC), molecular characteristics overrode concentration effects as the dominant risk factor. The established dose-structure-toxicity-risk evaluation framework provides a novel methodological system for health risk assessment of atmospheric nitrophenols.