Origin of Tar Balls Along the Beaches of Genaveh Region, Persian Gulf.

Abstract

Oil spills and tarballs are significant pollutants in marine environments, and identifying their sources is crucial for mitigating environmental impacts. This study aims to determine the primary sources of petroleum spills and tarballs along the shores of Genaveh (northwest of the Persian Gulf) by employing chemical fingerprinting techniques and biomarkers. Specifically, petroleum hydrocarbons were analyzed in 19 tarball samples, 13 surface sediment samples from the Genaveh coast, and reference oil samples from 21 offshore oil platforms located in the Bahregan, Khark, Lavan, Siri, and Hendurabi regions. Samples were extracted using the Soxhlet extraction method, followed by two-step column chromatography, and the compositions of n-alkanes, polycyclic aromatic hydrocarbons (PAHs), hopanes, and steranes were determined using gas chromatography-mass spectrometry (GC-MS). The concentration of PAHs in coastal sediment samples from Genaveh ranged from 345 (S841) to 27,374 ng/g-dw (S852), indicating moderate to very high pollution levels. The total concentration of aliphatic hydrocarbons in coastal sediment samples from Genaveh ranged from 8,694 (S842) to 27,374 µg/g-dw (S851), significantly exceeding n-alkane concentrations reported in surface sediments from many other regions worldwide, suggesting considerable pollution levels. For the 19 collected tarball samples, PAH concentrations varied from 597.5 to 10,173 ng/g-dw, while n-alkane concentrations ranged from 27,136 to 66,341 µg/g-dw, which may indicate differences in age or freshness. Diagnostic indicators, such as undifferentiated complex mixtures (UCM), a carbon preference index (CPI) close to 1 for n-alkanes, diagnostic ratios of PAHs, and ratios of hopanes and steranes, pointed to a predominantly petrogenic origin of hydrocarbons in the coastal sediments of Genaveh. The principal component analysis (PCA) results revealed a distinction between oil samples from the Lavan, Hendurabi, and Siri platforms, indicating oil leakage from the Khark oilfield pipelines (Doroud and Forouzan) and Bahregan oilfields (Bahregansar and Soroosh) as a major pollution source. This implies that both oil spills, observed in the coastal sediments of Genaveh, and episodic spills, represented by tarballs, originate from a similar, homogeneous source. Only sediment samples from stations S841 and S812 were not influenced by tarballs, suggesting pollution from a different source compared to other sediment samples.