Evaluation of anthropogenic inputs of hydrocarbons in sediment cores from a tropical Brazilian estuarine system

Abstract

Sources and historical deposition of aliphatic and polycyclic aromatic hydrocarbons (PAHs) were investigated in sediment cores from the tropical Mundaú–Manguaba estuarine-lagoon system (MMELS), an important and representative ecosystem of Brazil. The MMELS has approximately 30% of its areas covered of sugar-cane monoculture. Anthropogenic inputs from sugar-cane processing and urban growth can pose environmental problems. The short cores from MMELS were collected in 2007 at four sites: Manguaba Lagoon (C03 and C09), Mundaú Lagoon (C07) and Mundaú River (C08). The analytical method was evaluated for n-alkanes and PAHs, the recoveries of the samples demonstrated good accuracy (mostly above 70% recovery) and precision (below 30%). The total aliphatic hydrocarbon (TAH) concentrations ranged from 27.8 to 139.5μgg−1. Only core C07 presented values above 100μgg−1, being considered contaminated by aliphatic hydrocarbon. The presence of the unresolved complex mixture (UCM), hopanes and steranes indicated petrogenic contribution. The characteristics of n-alkanes based on the terrigenous/aquatic ratio (TAR), carbon preference index (CPI) and average chain lengths (ACL) showed that the terrigenous input was predominant. The Σ16PAH concentrations ranged from 29.2 to 222.7ngg−1, and thus the sediments are considered slightly polluted. The abundance of perylene compared to other PAHs can be used as an indicator of natural origin of this compound. The MMELS cores showed concentrations of perylene greater than 10% of the total penta-aromatic isomers, indicating natural contribution of this compound. The lowest values of Σ16PAH and perylene were found for core C07, nevertheless the higher values of TAH, UCM, hopanes and steranes were observed. The PAH isomeric ratios reflected a pattern of mainly pyrogenic input (petroleum, coal and biomass combustion). The potential ecosystem risk assessment indicated for PAHs is considered relatively low in MMELS. Despite the industry and the sugar-cane monoculture, the system did not show elevated or alarming data.