Evaluation of the organic matter sources and δ13C composition of individual alkanes for the baseline assessment of hydrocarbons in a pristine area from Amazon region, Brazil

Abstract

This study focuses on the surroundings of the Urucu oil and gas province and the adjoining Solimoes terminal in the Amazon region of Brazil, which is of great global importance due to its biodiversity richness and freshwater resources. There are few results related to aliphatic hydrocarbons and polycyclic aromatic hydrocarbons (PAHs), and there are no results for individual stable isotopic compositions (δ13C) in the studied region. Results showed a distribution of n-alkanes that is characteristic of a major input from higher plants. Furthermore, δ13C values of individual n-alkanes varied between −35.0 and −23.1 ‰, suggesting a dominance of 12C-enriched n-alkanes indicative of an origin from lacustrine algae. The levels of some PAHs (4.64–31.70 ng g−1) which are classified as priority pollutants by the United States Environmental Protection Agency (US-EPA) and perylene (biogenic PAH) were measured in surface sediments to identify pollution sources and determine baseline data looking for future management strategies. The majority of the compounds present in the samples from Coari Lake and the Solimoes River are of biogenic origin. However, a minor anthropogenic contribution of aromatic hydrocarbons derived from biomass burning (anthracene, phenanthrene, fluoranthene, pyrene, chrysene, benzo[b]fluoranthene and benzo[k]fluoranthene) was detected. No petrogenic contribution was found in the samples.