Discovery of Emerging Aromatic Compounds with High Potential Risk from Coal-Fired Power Plants

Coal combustion releases aromatic compound (AC) mixtures far more complex than the 16 EPA-priority polycyclic aromatic hydrocarbons (PAHs). Here, a high-resolution in-house database targeting 104 aromatic compounds prioritized by structural carcinogenicity alerts and structural analogy was developed to complement NIST library matching for screening fly ash, slag, and soil from five coal-fired power plants (CFPPs). This dual-database strategy increased the identification rate by 9.2% and captured 29 compounds previously unreported in the analyzed CFPP-related matrices. A total of 393 ACs spanning 24 structural classes were annotated. Cross-matrix profiling revealed distinct chemical shifts, from primary 1-ring products in slag to secondary chlorinated species in fly ash and ultimately to persistent high-molecular-weight PAHs in soils, suggesting that the observed AC patterns were associated with differences in unit efficiency, end-of-pipe control, and operational history across the five CFPPs. Incremental lifetime cancer risk assessment demonstrated that emerging PAHs contributed 60% of the total carcinogenic risk in fly ash despite comprising only ∼2% of total AC concentrations, with 4-ring compounds identified as the predominant risk drivers. Sensitivity analysis confirmed that assessments restricted to literature-derived toxic equivalency factors underestimate the full carcinogenic potential. These findings reveal a critical yet underrecognized toxic fraction in CFPP fly ash, underscoring the need for risk-oriented management strategies that explicitly incorporate emerging PAHs.