Carbon isotope evidence for oil-pollution in long chain normal alkanes in Tokyo Bay sediments

Abstract

Carbon isotope compositions of long-chain n-alkanes (C₂₇∼C₃₃) in selected samples from a Tokyo Bay sediment core (0∼3 m in depth) were determined by gas chromatography/isotope ratio mass spectrometry (GC-IRMS). δ¹³C values of the n-alkanes in the shallow sections (0∼40 cm in depth, present∼1965 AD) range from –31.5 to –28.2‰ relative to the PDB standard, showing that even carbon-numbered n-alkanes are isotopically heavier than the odd numbered ones. The n-alkanes in the deeper sections (190∼220 cm in depth) show the values ranging from –29.6 to –31.4‰ (average value: –30.7 ± 0.6‰) without any significant difference among the n-alkanes. The results of n-alkanes in the shallow sections are explained by an addition of oil-derived n-alkanes to higher plant wax n-alkanes observed in the deeper sections.