Fate modeling and spatial health risk assessment of urban polycyclic aromatic hydrocarbons using a kilometer-resolution multimedia model

• Compartmental PAH concentrations followed a consistent sequence of organic film > sediment > soil > vegetation > water > atmosphere. • All health endpoints exhibited age-dependent risk stratification ordered adult > adolescent > child. • Benzo[a]pyrene (54.12–56.10 %) and dibenz[a,h]anthracene (20.47–23.39 %) dominated cumulative toxicity contributions. Polycyclic aromatic hydrocarbons (PAHs), as highly carcinogenic persistent pollutants, pose challenges for assessing urban multimedia distribution and exposure risks due to limited spatial resolution of conventional models. Traditional fugacity models, constrained by homogeneity assumptions, fail to capture environmental heterogeneity in high-density cities. This study developed a kilometer-resolution steady-state multimedia model to characterize the fate and health risks of PAHs in Nanjing, with model predictions validated against measured concentrations across 13 environmental compartments. The results reveal a distinct concentration hierarchy: organic film > sediment > soil > vegetation > water > atmosphere. Organic film (57.2–68.7 %) and water (28.5–37.5 %) are the dominant contributors to incremental lifetime cancer risk (ILCR), highlighting their priority for risk management. Health risks exhibit significant age differentiation: children are more sensitive to atmospheric PAH exposure, adolescents are predominantly affected by soil, vegetation, and organic film, and overall ILCR follows the gradient Adults > Youths > Children (ranging from 1.22 × 10 –9 to 4.00 × 10 –5 ), driven by age-dependent behavioral and physiological differences. Among individual PAHs, BaP (54.12 %-56.10 %) and DahA (20.47 %-23.39 %) dominate cumulative toxicity risks. Assessment of eight toxicity endpoints identifies respiratory toxicity, carcinogenicity, estrogen receptor toxicity, aryl hydrocarbon receptor toxicity, and antioxidant response disruption as core health impacts, primarily driven by high-molecular-weight PAHs. This high-resolution modeling framework enables precise identification of urban PAH pollution hotspots and age-specific exposure risks, providing critical scientific support for targeted pollution control and public health protection in high-density cities.