Characterization of organic matter in a sediment Core near the Mataripe refinery, Bahia–Brazil

•Changes in organic matter were observed along the core in Todos os Santos Bay.•The sedimentation rate was determined with 210Pb calibrated with 137Cs peak.•Dating showed that from 1942 there was increasing the organic matter.•The increase in organic matter beginning of production of the oil fields.•The increase in polycyclic aromatic hydrocarbons marked the beginning anthropogenic influence.

A sediment core was taken from the Todos os Santos Bay, near the Mataripe Bahia‐Brazil refinery. The results of dating, 210Pb and 137Cs methods, combined with organic indicators, Polycyclic aromatic hydrocarbons (PAHs), n-alkanes and total organic carbon (TOC), showed significant change with the start of production of the oil fields of Aratu, Itaparica and Dom João (1939‐1947) and the construction of the Mataripe refinery (1949‐1950). This event was marked by a series of significant changes, including an abrupt increase in TOC and the growth of PAH concentrations and the presence Unresolved/Resolved ratio (UR/R) > 4 in n-alkanes fraction, which indicated that the contamination was of petrogenic origin.The δ13C of specific n-alkanes compounds showed gradual deplete with the depth.