Investigação da introdução da matéria orgânica no sedimento do Rio Paraibuna e o papel dos hidrocarbonetos alifáticos como marcadores biogeoquímicos no monitoramento de contaminações antrópicas

Abstract

In this work, it was performed the determination of n-alkanes (C10-C40) biomarkers crude oil and its derivatives, in river sediment samples. The sampling was performed with 16 points along Paraibuna river in Juiz de Fora-MG, collected with Petersen dredge. A 33 Box-Behnken experimental design was used to optimize the ultrasound-assisted extraction conditions. The optimized conditions was 10 minutes of sonication with 10 mL solvent mixture and the mixture composition was n-hexane and acetone (25:75). The extracts were eluted in an adsorption column containing silica, alumina and sodium sulfate, using 16 mL of n-hexane for total elution of the extract. The eluated analysis was performed by gas chromatography coupled with mass spectrometry. In addition, it was verified the sediment granulometry and the total organic carbon (TOC) determination for each sampling. We obtained a strong correlation between TOC and the silt + clay. In general, Paraibuna river’s sediment are basically constituted by sand. For points that the concentration of silt + clay were low, it was not possible to detect several analytes. The concentration of total aliphatic ranged from 0.78 to 1318.18 μg g-1 dry weight and the total n-alkanes ranged from 0.07 to 5.49 μg g-1 dry weight, being observed an increase in the concentration of compounds in the direction of river flows. The obtained carbon preference index ranged from 0.94 to 4.75, indicating introduction of n-alkanes by anthropogenic sources for some samples. From the 16 collected points, 12 presented an unresolved complex mixture, being 50% of unimodal profile and 50% bimodal, as result of pollution from fuel oil and other petroleum derivatives. In all points, it was observed the domain of terrigenous sources contributions over the aquatic sources.