Levels and Sources of Hydrocarbons in the Patos Lagoon Estuary and Cassino Beach Mud Bank (South Atlantic, Brazil): Evidence of Transference Between Environments

This study aimed to evaluate the concentrations and sources of natural and anthropogenic aliphatic (AHs) and polycyclic aromatic hydrocarbons (PAHs) in surficial sediments collected along the Patos Lagoon estuary and in sediment cores obtained from the Cassino Beach mud bank. Levels and distribution of n -alkanes indicate terrestrial sources, overlapping with a low amount of petrogenic hydrocarbons (heavy oils). A small unresolved complex mixture (UCM) was observed in all samples. On the other hand, the distribution of PAHs in the sediments showed a predominance of pyrolytic over petrogenic sources. In general, hydrocarbons (HCs) contamination in the Patos Lagoon estuary and its adjacent coastal area can be considered low, except for sites near urban or industrial effluents, where moderate to high levels of contamination were found. Concentrations of HCs were homogeneous throughout the sediment cores, suggesting that mixing processes may have occurred along the layers or that HCs inputs to the mud banks were uniform during the studied deposition period. In addition, the levels and profile of HCs levels in the coastal sediments were similar to those observed in the estuary, suggesting that HCs are promptly exported without any significant dilution and/or degradation during this process. Moreover, the frequent remobilization of sediments from the mud bank towards Cassino beach does not seem to pose any threats to the local biota or beach users since the levels of contamination were relatively low.