Extraction and Determination of Aliphatic Alkanes in Marine Sediment Samples from the Coast of Tripoli (Libya)

Abstract

This study, conducted on sediments from the coast of Tripoli, Libya in 2025, aimed to monitor marine pollution by assessing the spatial distribution and molecular composition of PAH  (normal alkanes C9–C20) in surface sediments.  Total organic carbon (TOC) was measured, and hydrocarbons were analyzed using gas chromatography-mass spectrometry (GC-MS). Results showed that sediments were predominantly sandy (89.61%–99.8%), indicating a high-energy hydrodynamic environment that limits organic matter accumulation, as reflected by low TOC values (0.023%–0.079%). Statistical analysis revealed a strong negative correlation between sand and TOC (r = -0.84) and a positive correlation between silt and TOC (r = 0.79), confirming the role of fine particles in retaining organic matter. Total alkanes (∑C9–C20) ranged from 1510.1 to 8812 ng/g, with an average of 4770 ng/g, showing high spatial variability (coefficient of variation = 60.8%), suggesting the influence of local pollution sources. The highest concentrations were recorded at stations S5, S4, and S7, indicating accumulation zones linked to marine activities. Molecular distribution was dominated by long-chain alkanes (C15–C20), reflecting terrestrial petroleum and plant inputs, while lighter compounds (e.g., C9) at some sites indicate recent contamination. Correlation analysis showed a strong relationship between hydrocarbons and clay (r = 0.822), but a weak relationship with TOC (r = 0.079), indicating that hydrocarbon distribution is mainly controlled by sediment texture and external inputs. These findings highlight the combined influence of sediment characteristics, hydrodynamics, and human activities, emphasizing the need for continuous monitoring and sustainable coastal management.