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 spec trometry (GC-IRMS). 813C values of the n-alkanes in the shallow sections (0 40 cm in depth, present --1965 AD) range from -31.5 to -28.2%o 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%o (average value: -30 .70.6%o) 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 ob served in the deeper sections.