Carbon isotope signature of polycyclic aromatic hydrocarbons (PAHs): evidence for different sources in tropical and temperate environments?

In tropical soils, naphthalene and, partly also, perylene occur at elevated concentrations while pyrolytic higher molecular weight PAHs are almost absent. We hypothesize that there are recent biological PAH sources in the tropical environment related with woody plants and termites. We used the C isotope signature of individual PAHs in temperate and tropical soils and in tropical wood and termite nests to distinguish different PAH sources. The mean delta13C values of the benzo[b+j+k]fluoranthenes and of benzo[a+e]pyrenes in temperate soils ranged between -24.6/1000 and -25.3/1000, being similar to values reported in the literature for PAHs with pyrolitic origin. The mean delta13C values of perylene decreased in the order temperate soils (-27.0/1000) > termite nests (-31.4/1000) > tropical soil (-32.4/1000), while those of naphthalene (-24.6/1000 to -26.2/1000) were similar among the tropical and temperate soils, tropical wood, and termite nests. Our results support the assumption that perylene in the tropical environment is recently biologically produced, as indicated by the depletion in 13C. The C isotope composition of naphthalene, however, cannot be used to distinguish different sources.