Occurrence and characterisation of naphthenic acid fraction components in oil residues stranded on the shoreline of Chedabucto Bay, Nova Scotia, Canada

Abstract

Purpose This study aimed to investigate the occurrence, fate, and behaviour of oil components 46 years post-spill by analysing polar naphthenic acid fraction components (NAFCs). Methods Oil residues and sediment samples were collected from the shoreline of Chedabucto Bay, Nova Scotia, Canada, at sites affected by the 1970 Arrow oil spill, in June 2016. Sediments were extracted with Soxhlet extraction; NAFCs were separated through a silica gel column firstly, then analysed by high-performance liquid chromatography–high-resolution mass spectrometry (HPLC-HRMS). Results and discussion In all samples, the most abundant NAFC species were those having only oxygen as the heteroatom (Oo species, o indicating the number of oxygen atoms, from 1 to 8) and a high degree of saturation. O2 species accounted for 50–70% of all Oo species. NAFCs with sulphur heteroatoms were the second abundant species, then by those containing both nitrogen and oxygen heteroatoms. NAFCs in most Arrow oil residues had higher levels of oxygen species, especially for heavier molecular weight congeners, than the oil remaining stored in the sunken tanker. Environmental sediment samples, collected from near a marina away from the spill site, mainly contained a biological contribution with obviously recent petroleum oil input, whereas all Arrow oil residues were composed mainly of NAFCs that are characteristic of petroleum, and varied abundance between sites. Conclusions Characteristics of NAFCs from different sources varied from each other. Site-specific environmental conditions played a major role in controlling the fate and behaviour of oil components, including NAFCs.