Vertical distributions and δ13C isotopic compositions of PAHs in Chidorigafuchi Moat sediment, Japan

Compound-specific carbon isotope analysis and molecular composition analysis were performed on polycyclic aromatic hydrocarbons (PAHs) extracted from a dated 50 cm sediment core from the Chidorigafuchi Moat, Japan. δ13C values ranged from −23.0 to −26.9‰ for individual PAHs, and ranged from −24.0 to −25.5‰ for the weighted average of PAHs at different core depths. Whilst total PAH concentrations showed a distinct maximum at around the year 1960, δ13C values did not show a statistically significant feature in the corresponding section of the core. Indeed, there was little correlation (r2=0.12, P=0.19) between ΣPAH and δ13C throughout the core. PAHs in surface sediment (ca 0–8 cm) were characterised by a significantly higher benzo(ghi)perylene to indeno(1,2,3-cd)pyrene ratio (t-test, P<0.025) and heavier δ13C values (P<0.015) than lower sections in the core. This suggests that PAHs sedimented after 1990 were more strongly influenced by PAHs from automotive exhausts. This preliminary study suggests that a two-dimensional analysis of both the molecular and isotopic compositions of PAHs may be useful in obtaining a more detailed source identification of organic pollutants in environmental samples.