Evaluation of the organic matter sources using the δ13C composition of individual n-alkanes in sediments from Brazilian estuarine systems by GC/C/IRMS

The delta C-13 composition of individual n-alkanes (from C-16 to C-34) was measured from surface sediments of five Brazilian estuarine systems affected by different organic matter sources, such as harbor area, industries, urban centers and sugar cane crops, in order to determine the origins of the organic matter. The aliphatic hydrocarbon fraction was analyzed by gas chromatography-combustion-isotope ratio mass spectrometry (GC/C/IRMS). The levels of n-alkanes in the studied areas ranged from 0.34 to 18.14 mu g kg(-1), being relatively low in comparison to high polluted environments. The Carbon Preference Index (CPI) calculated in the C-23-C-34 range indicates that n-alkanes are mainly inherited from cuticular waxes of higher plants. The delta C-13 composition of all n-alkanes detected in the sediment samples ranged from -39.6 to -18.3 parts per thousand showing different sources for the studied estuarine systems. Through Principal Component Analysis (PCA) it was possible to verify the petrogenic influence in the n-alkane sources, especially in the Paraiba do Sul sediment samples. Differences up to 15 parts per thousand of the delta C-13 values between n-alkanes of odd and even carbon number (C-26 and C-27) also indicated mixture of petrogenic and biogenic sources in Paraiba do Sul River. High (less negative) delta C-13 n-alkane values of odd carbon number were obtained from two sampling sites located close to an ethanol plant, indicating residues discharge of sugar cane (C-4 plant). Influence of C-3 plants that are the main components of dense ombrophile forest was observed in the Itajai-Acu sediments by the decrease of delta C-13 (about 10 parts per thousand compared to the Paraiba do Sul River delta C-13). (C) 2012 Elsevier Ltd. All rights reserved.