Evaluation of tools to identify hydrocarbon sources in recent and historical sediments of a tropical bay

A number of diagnostic ratios have been applied as tools to distinguish provenance of hydrocarbons in sediments. In the present work the effectiveness of such ratios as source indicators under tropical conditions is evaluated using aliphatic and aromatic hydrocarbons determined in recent and historical sediments from the Todos os Santos Bay (TSB), Brazil. It turned out that substantive alteration of the original hydrocarbon composition often produced misleading results and that source evaluation in sediments required more complex approaches. In surface sediments sampled in summer and winter Total PAH (sum of parental and alkylated PAH) ranged from 42 µg kg− 1 to 3335 µg kg− 1 and from 64 µg kg− 1 to 4187 µg kg− 1, respectively. In most cases diagnostic ratios pointed out incomplete combustion as the single or major PAH source while detailed data examination revealed ubiquitous presence of oil residues. The same observation holds for some of the examined cores. The mean (n = 8) Total PAH flux in recent times is of 608 ± 741 ng cm− 2 year− 1. There are indications in some cores that the relative contribution from combustion sources were more pronounced in the past, as for instance, the continuous decrease of B(a)Py fluxes from 92 ng cm− 2 year− 1 in the 1900s to 23 ng cm− 2 year− 1 in the 2000s.