Hydrocarbons in fish tissues: a group-type approach

Petroleum hydrocarbons extracted from biological samples usually contain interfering biogenic compounds similar in structure to petroleum compounds. For the determination of total petroleum hydrocarbons (TPHs) in biota without biogenic distortions, we implemented an approach based on the mass-spectrometric group-type analysis in combination with common n-alkanes determination. The approach proved to be promising, allowing the identification and estimation of the content and molecular mass distributions of the main groups of hydrocarbons and heteroatomic compounds. The sum of all determined hydrocarbon groups in Coregonus sardinella from the Pyasina River after the accidental diesel fuel spill in Norilsk in 2020 determined by this approach was 3.5 μg/g, while the total organic compound content of the extract eluted in the petroleum hydrocarbons range was 15.4 µg/g. Thus, an integral TPH measurement would result in an almost fivefold overestimation of the contamination level. The content of n-alkanes was 7.1 µg/g and their distribution reflected the contribution of several biogenic sources. Petroleum compounds in the fish sample were consistent with the composition of medium oil fractions and included isoalkanes, cycloalkanes with 1–3 condensed cycles, alkylbenzenes, naphthene- and dinaphthenebenzenes, naphthalenes, acenaphthenes/biphenyls, fluorenes, phenanthrenes, naphthenephenanthrenes, fluoranthenes/pyrenes, and traces of dibenzothiophenes. Aromatic compounds accounted for about 26%, PAHs—for 7.6%, the content of unsubstituted naphtalenes was relatively small, and the bulk of them was represented by molecules with 3–12 C atoms in alkyl substituents. The maxima of molecular mass distribution within the determined groups were shifted by 1–3 C atoms to a heavier region compared to diesel fuel, which is characteristic of weathered petroleum products.