Caracterização de fontes de contaminação no semi-árido cearense, utilizando hidrocarbonetos de petróleo (Rio Acaraú – Ceará)

Abstract

Distribution, composition, sources and factors controlling accumulation and distribution of PAHs, alkanes, isoprenoids (pristane and phytane) and oil biomarkers (hopanes and steranes) were investigated in surface sediments and in a sedimentary profile at Acaraú river which is the second largest drainage basin of Ceará. In surface sediments, the sum of the concentration of the series of C10 -C38 n-alkanes ranged from approximately 3,000 ng.g-1-8000 ng.g-1, averaging 5405.77 ng.g-1; since the sum of the 16 priority PAHs USEPA ranged from 141.43 ng.g-1 (ACR3) to 2077.20 ng.g-1 (ACR5). On the other hand, the hopanes ranged from <LOD (ACR3) to 67.87 μg.g-1 (ACR6), especially the C29-hopano (NH) and steranes presented values ranging from <LOD to 23.27 ug .g-1 (ACR4), highlighting the C28αββ (S / R). For the characterization of the primary sources in the basin of Acaraú were used various diagnostic ratios as Σ PAHs (4-6 rings) / Σ HPAs16, BaA / (BaA + Cri), IP / (IP + BghiP), Phe / Ant, Fltr / Pir% Per / 5 rings, CPI (15-19), CPI (25-33), nC17/Pr, nC18/Fit and Pr/Fit. According to the Carbon Preference Index, most stations showed CPI ~ 1, which features possible source of oil derivatives, which was confirmed by the presence of hopanes and steranes at most stations. Moreover, analysis of PAH returned pyrolytic primary sources that can be related to the burning activities in the region, as the use of wood for cooking and energy source and vehicle emissions. Regarding the assessment of the potential risk to the ecosystem, most stations were below the lower level (TEL) established by the Canadian Environmental Agency with low probability of adverse effects to biota. Only at ACR8 site, the compounds fluorene and dibenzo(a,h)anthracene had possible adverse effects on biota. The historical record in the estuary of the River Acaraú revealed the predominance of pyrolytic sources in deeper layers, probably related to encouraging the use of wood as an energy source in the seventies due to the oil crisis. Furthermore, the deposition of PAHs was determined by the grain size and the organic carbon content, with a probable relationship with the organic matter adsorbed in the clay minerals.