Coari Lake is a critical area in the Amazon due to the oil exploration that began in the 1980s. The present study evaluates the impact on Coari Lake and the Solimões River in order to identify the origin of the sedimentary organic matter. This research is of great importance as it constitutes a crucial follow-up assessment, conducted 13 years after the initial survey by the same research group. Aliphatic hydrocarbons found in the new collected samples ranged from n-C14 to n-C34, with Cmax at C29–C31 and CPI values between 2.5 and 5.1, suggesting predominantly terrestrial biogenic inputs. Although the total n-alkane concentrations increased from 2012 to 2025, values remained within natural background ranges and as well as those ones associated with contaminated sediments. Aromatic hydrocarbons were strongly dominated by perylene, further supporting a biogenic origin. Monoaromatic and polyaromatic triterpenoids derived from α-amyrin, β-amyrin and lupeol were consistently detected, reflecting contributions from higher-plant material. No petrogenic indicators such as hopanes, steranes or unresolved complex mixtures were identified in any sample. Principal Component Analysis confirmed a temporal increase in hydrocarbon abundance while maintaining stable source signatures. Overall, the results demonstrate that Coari Lake sediments are still dominated by natural organic matter.
Andrade et al. (Wed,) studied this question.