Evaluation of tools to identify hydrocarbon sources in recent and historical sediments of a tropical bay Angela Wagener ⁎, Claudia Hamacher, Cassia Farias, Jose Marcus Godoy, Arthur Scofield Departamento de Química, Pontifícia Universidade Católica do Rio de Janeiro, 22453-900 Rio de Janeiro, Brazil abstract article info Article history: Received 29 July 2009 Received in revised form 15 March 2010 Accepted 15 March 2010 Available online 27 March 2010 Keywords: Hydrocarbons Diagnostic ratios PAH Marine sediments Tropical region 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. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Over the last 20 years the largest increment in known petroleum reserves in the world occurred in Brazil where major oil reservoirs are found offshore. The fast development in oil exploration for internal uses or exportation is associated with an increasing risk in contamination of coastal areas with oil derived hydrocarbons. Polycyclic aromatic hydrocarbons (PAH) are among the most toxic components of oils but can also be produced due to incomplete combustion of organic matter and during diagenesis of biogenic precursors (Venkatesan, 1988; Wang et al., 1999). Despite the need to distinguish different PAH sources to implement actions for pollution prevention and abatement few in situ studies have been performed to understand the behavior of oil components in tropical marine environments (Farias et al., 2008) and the effects of extensive weathering upon the oil identity. Studies on PAH levels and source evaluation in tropical regions (i.e. Macías-Zamora et al., 2002; Olajire et al., 2005; Anyakora et al., 2005a,b; Meniconi and Barbanti, 2007; Gaspare et al., 2009) are scarce in comparison to those performed in higher latitudes. Except for Menconi and Barbanti, these reports focus on the 16 parental PAH that were prioritized by the USEPA due to their toxicity and in some cases few selected alkylated PAH homologues are included. Because light parental PAH which are most abundant in oils are weathered at faster rates than the high molecular weight PAH the use of diagnostic ratios based on pairs of parental PAH may lead to ambiguous interpretation. Determi- nation of alkylated PAH homologues which also predominate in oil residues provides a more solid basis for estimating the relative importance of pyrogenic and petrogenic PAH inputs to the environment (Wang et al., 1999). Diagnostic ratios have been proposed as tools to sort out the origin of PAH contamination (Garrigues, et al., 1995; Budzinski et al., 1997; Wang et al., 1999; Yunker et al., 2002). In all cases source characterization is based on diagnostic ratio thresholds derived on the basis of the original composition of oils and pyrogenic products, and on data obtained in matrices from temperate climate. The diagnostic ratios are calculated as the relation between isomers as for instance, phenanthrene/anthracene, fluoranthene/ pyrene, anthracene/mz 178 and benz(a)anthracene/mz 228 (Baumard et al., 1998; Yunker et al., 2002). Such and other ratios have been useful in distinguishing petrogenic from pyrogenic PAH as well as in discriminating PAH formed in fossil fuel combustion from those produced in wood, coal or grass combustion (benzo(b)fluoranthene/ benzo(k)fluoranthene, indeno(1,2,3-c,d)pyrene/benzo(g,h,i)pery- lene, among others; Dickhut et al., 2000). The ratio of alkylated to parental PAH can be used as indicator of petroleum sources since the former compounds are most abundant in oils while parental homo- logues are preferably formed during incomplete combustion (Wang et al., 1999). Marine Chemistry 121 (2010) 67–79 ⁎ Corresponding author. Rua Marques de São Vicente, 225, 22543-900 Rio de Janeiro, Brazil. Tel.: +55 21 3527 1809; fax: +55 21 2239 2150. E-mail addresses: angela@puc-rio.br (A. Wagener), claudiahamacher@petrobras.com.br (C. Hamacher), cassiafarias@puc-rio.br (C. Farias), jmgodoy@puc-rio.br (J.M. Godoy), scofield@esp.puc-rio.br (A. Scofield). 0304-4203/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.marchem.2010.03.005 Contents lists available at ScienceDirect Marine Chemistry journal homepage: www.elsevier.com/locate/marchem