Establishing Criteria of Relative Abundance of Alkyl Polycyclic Aromatic Hydrocarbons (PAHs) for Differentiation of Pyrogenic and Petrogenic PAHs: An Application to Indian Sediment

Various source materials such as crude oil, automobile exhaust, coal, and wood combustion products were analyzed for polycyclic aromatic hydrocarbons (PAHs) and hopanes. Hopanes were detected in coal combustion-derived soot, along with petrogenic sources. Based on the correlation between the alkylated PAHs/parental PAHs ratio with their respective C30 hopane/PAHs ratio in these source materials, the criteria for differentiating the petrogenic and pyrogenic sources of PAHs were established. This study concluded that sediments contained exclusively pyrogenic PAHs when the following conditions were met: MP/P (methylphenanthrenes to phenanthrene) = 0.5, MPy/Py [(methylpyrenes + methylfluoranthenes) to (pyrene + fluoranthene)] = 0.15, and MC/C [(methylchrysenes + methylbenz[a]anthracenes) to (chrysene + benz[a]anthracene)] = 0.2. By contrast, the sediments contained exclusively petrogenic PAHs when the ratios of MP/P, MPy/Py, MC/C, and methyl PAHs (MPAHs)/PAHs exceeded 3.5, 1.5, 2.0, and 2.2, respectively. Based on these criteria, an intensive source apportionment of PAHs to sediments from three Indian metro cities, Chennai (n = 6), Mumbai (n = 6) and Kolkata (n = 12) (2003–2007), was determined. This investigation found that sedimentary PAHs from India were depleted in alkylated PAHs with low MP/P ≈ 0.7, MPy/Py ≈ 0.14, and MC/C ≈ 0.3, which contrasted with other tropical Asian countries, where elevated values of these ratios were detected. Among the three cities, Kolkata waters were more strongly influenced by pyrogenic sources of PAHs with very low alkylated PAHs ratios than Chennai and Mumbai sediments. The compositional differences were attributed to the dominant coal and biomass in Kolkata compared to the dominant usage of petrogenic cooking fuel (e.g., kerosene) and automobile-derived sources in Chennai and Mumbai.