Spatio-temporal variability, distribution and sources of n-alkanes and polycyclic aromatic hydrocarbons in reef surface sediments of Kharg and Lark coral reefs, Persian Gulf, Iran

Abstract

Environmental pollution, particularly oil pollution, has been a long-standing problem in marine areas. With the aim to assess the pollution status in the Persian Gulf, Iran, herein surface sediments were collected from Kharg and Lark coral reefs, in summer (dry season) and winter (wet season), to evaluate the spatio-temporal variations of n-alkanes and PAHs. The mean total organic carbon (TOC) contents of sediments showed a significantly dramatic variation (p < 0.05) in both seasons at both Islands, with high values recorded at sites located near pollutant inputs. The total mean percent of clay grain-sized sediments at Kharg were 26.57% and 28.86% in dry and wet seasons, respectively, while in Lark were 26.73% in summer and 24.57% in winter. Additionally, at Kharg the mean ∑25n-alkanes and ∑30PAHs ranged from 81.35 to 573 µg g−1 dw and 60.25–491 ng g−1 dw in dry season, and 171–754 µg g−1 dw and 41.61–693 ng g−1 dw in winter, respectively. At Lark, the average ∑25n-alkanes and ∑30PAHs varied from 31.18 to 272 µg g−1 dw and 41.25–196 ng g−1 dw in summer, whilst oscillated from 57.99 to 332 µg g−1 dw and 16.56–487 ng g−1 dw in wet season, respectively. The lowest mean level of the examined pollutants were spanned in offshore sites, while the highest average concentrations indicated that contaminated sediments were at onshore stations at both Islands in both seasons. Significant seasonal variations (p < 0.05) were observed at most sampling sites for all pollutants. Molecular Diagnostic Ratio (MDR) and Principal Component Analysis (PCA) indicated that n-alkanes and PAHs had mostly a petrogenic source. The compositional profile of PAHs showed that 2 and 3-ring PAHs were abundant at both sampling sites. Significant positive correlation (r > 0.76) was observed between ∑25n-alkanes and ∑30PAHs at Kharg and Lark sediments with TOC content, especially for the sites with high total pollutant concentrations. Based on the potential impact and ecological risk of n-alkanes and PAHs in surface sediments, it is, therefore, necessary in future studies to focus on their effects on corals and other marine organisms within this ecosystem.