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 fromautomotive 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.