Heterocyclic aromatic compounds in Lake Ontario sediments: Spatiotemporal distribution and new approaches to fingerprinting

Hetero-polycyclic aromatic compounds (HPACs), an understudied subclass of polycyclic aromatic compounds (PACs), are characterized by the replacement of one or more carbon in their aromatic ring structure with nitrogen, sulfur, and/or oxygen. This study examined the spatiotemporal distribution of fifty HPACs in sediment samples from Hamilton Harbour (HH), Toronto Harbour (TH), and nearby non-Harbour areas of Lake Ontario, proposing new approaches to fingerprinting PACs using HPACs. Although no temporal trends in HPAC concentrations were observed from 2014 to 2023, notable spatial differences were evident, with the rank order of total HPAC concentrations as HH > TH > non-harbour areas. Based on their higher source specificity relative to polycyclic aromatic hydrocarbons (PAHs), chemical fingerprinting using diagnostic ratio analysis, compositional analysis and multivariate analysis were performed. Results from an empirical approach, environmental data and physical-chemical properties were used to select analytes for fingerprinting. Diagnostic ratios between alkylated dibenzothiophenes and parent dibenzothiophene indicate lower ratios for coal tar contaminated sites than other sites, suggesting pyrogenic sources. Spearman's correlation between total combustion PAHs and HPACs indicates most analytes were derived from combustion processes. Principal Component Analysis (PCA) did not differentiate between sample HPAC fingerprints; samples separated in the first principal component were driven by total HPAC concentration and not variability in source fingerprint. Uniform Manifold Approximation and Projection (UMAP) provided a more detailed visualization, highlighting compositional differences between harbour sediments and non-harbour sites. Overall, these results highlight the usefulness and importance of using combined analytical approaches to fingerprint PACs using HPACs as chemical markers.