Evaluation of the Sources and Distribution of n-Alkanes in a Sediment Core from Khor Al-Zubair, Northwestern Arabian Gulf | ||||
| Egyptian Journal of Aquatic Biology and Fisheries | ||||
| Article 75, Volume 29, Issue 4, July and August 2025, Page 1333-1358 PDF (1.33 MB) | ||||
| DOI: 10.21608/ejabf.2025.443089 | ||||
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| Author | ||||
| Abo-Turab et al. | ||||
| Abstract | ||||
| Five sediment core samples were collected from various locations in Khor Al-Zubair, in the northwestern part of the Arabian Gulf, to evaluate the sources and distribution of n-alkane concentrations in the study area. Hydrocarbon compounds were extracted from the sediment samples and analyzed using gas chromatography. A broad range of alkanes, from C₈ to C₄₀, was identified across the sampling locations. The concentration of n-alkanes varied widely, ranging from a low of 0.1828 µg/g at the third station (40–45 cm depth) to a relatively high concentration of 15.4762 µg/g at the fifth station (45–50 cm depth). In several stations and depths, the Carbon Preference Index (CPI) values were low, indicating potential petroleum pollution. CPI was calculated to determine the origin of the hydrocarbons found in the sediments. The C₁₇/pristane (C₁₇/Pri) ratio was lowest at the first station (0.50609) and highest at the second station (2.6675), while the C₁₈/phytane (C₁₈/Phy) ratio was highest at the first station (3.4841) and lowest at the fifth station. These ratios serve as useful indicators for distinguishing between biogenic and petrogenic sources of hydrocarbons. Lower molecular weight alkanes (C₁₀–C₁₅) are more prone to evaporation and microbial degradation, which explains their typically low concentrations. In contrast, higher molecular weight alkanes (C₃₃–C₃₆), being more resistant to degradation, tend to accumulate in the water column and sediments. Phytane is generally associated with petroleum sources, while pristane is often linked to zooplankton. In aquatic systems, odd-numbered alkanes such as C₁₅, C₁₇, and C₁₉ are commonly derived from phytoplankton and algal sources, whereas C₂₅, C₂₇, C₂₉, and C₃₁ are recognized as biomarkers of terrestrial plant material. Overall, the presence of hydrocarbons in the form of n-alkanes in this region is attributed to both anthropogenic activities—including vehicle emissions, oil spills, and industrial discharges—and natural sources, such as marine organisms, plankton, and terrestrial vegetation. | ||||
| Keywords | ||||
| N-alkanes; Khor Al-Zubair; Iraq; Sediment core; GC | ||||
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