Occurrence, sources and transport pathways of natural and anthropogenic hydrocarbons in deep-sea sediments of the eastern Mediterranean Sea

Abstract

Abstract. Surface sediments collected from deep basins (1018-4087 m depth) of the eastern Mediterranean Sea (Ionian Sea, southern Aegean Sea and northwestern Levantine Sea) were analyzed for aliphatic and polycyclic aromatic hydrocarbons as tracers of natural and anthropogenic inputs. Concentrations of total aliphatic hydrocarbons, n-alkanes and the unresolved complex mixture (UCM) of aliphatic hydrocarbons varied significantly, ranging from 1.34 to 49.2 µg g −1 , 145 to 4810 ng g −1 and 0.73 to 36.7 µg g −1 , respectively, while concentrations of total polycyclic aromatic hydrocarbons (PAHs) ranged between 11.6 and 223 ng g −1 . Molecular profiles of determined hydrocarbons reflect a mixed contribution from both natural and anthropogenic sources in deep-sea sediments of the eastern Mediterranean Sea, i.e., terrestrial plant waxes, degraded petroleum products, unburned fossil fuels and combustion of grass, wood and coal. Hydrocarbon mixtures display significant variability amongst sub-regions, reflecting differences in the relative importance of inputs from various sources and phase associations/transport pathways of individual hydrocarbons that impact on their overall distribution and fate. Hydrocarbon concentrations correlated significantly with the organic carbon content of sediments, indicating that the latter exerts an important control on their transport and ultimate accumulation in deep basins. Additionally, water masses' circulation characteristics also seem to influence the regional features and distribution patterns of hydrocarbons. Our findings highlight the role of deep basins/canyons as repositories of both natural and anthropogenic chemical species.

Composition and sources of sedimentary organic matter in the deep eastern Mediterranean Sea

“…UCM levels recorded in the deep EMS are comparable to those reported for surface sediments in unpolluted coastal and/or open-sea areas and are at least one order of magnitude lower than those reported for coastal areas subjected to enhanced anthropogenic inputs (Gogou et al, 2000;Parinos et al, 2013;Kaiser et al, 2014;Romero et al, 2015; and references therein). Two main pathways have been identified for the introduction of petroleum hydrocarbons into the deep EMS, which are direct discharges from merchant shipping and oil transportation (UNEP, 2010) and atmospheric transport and deposition (Gogou et al, 1996;Castro-Jiménez et al, 2012;Parinos et al, 2013).…”

“…cholesterol (cholest-5-en-3β-ol; Mar range between 18.2 and 72.6 µg g OC −1 , 43.6 µg g OC −1 on average (Fig. 4d and Table 3), displaying a generally increasing eastward trend with maximum concentrations (> 55 µg g OC −1 ) recorded in the deep north- Parinos et al (2013); b sum of the concentrations of C37 : 3M, C37 : 2M, C36 : 2FAME, C38 : 3Et, C38 : 3M, C38 : 2Et, C38 : 2M (the corresponding unsaturated homologues are indicated with the number of their carbon atoms (n) and the number of double bonds (x) − (Cn : x); M: methyl; Et: Ethyl; FAME: Fatty acid methyl ester); c sum of the concentrations of long-chain C 30 n-alkan-1,15-diols and C 30 keto-ols; d sum of the major C 27 -C 30 sterols considered in this study, i.e. cholesterol (cholest-5-en-3β-ol; 27 5 ), brassicasterol (24-methylcholesta-5,22-dien-3β-ol; 28 5,22 ), β-sitosterol (24-ethylcholesta-5-en-3β-ol; 29 5 ) and dinosterol (4α,23,24-trimethyl-5α(H)-cholest-22(E)-en-3β-ol -30 22 ).…”

“…F 1 and F 3 fractions were analysed by gas chromatography-mass spectrometry (GC-MS) while F 2 fractions were analysed by gas chromatography using flame ionization detection (GC-FID). Hydroxyl-bearing compounds (fraction F 3 ) were derivatized to the corresponding trimethylsilyl ethers prior to GC-MS analysis using N,O-bis-(trimethylsilyl)-trifluoroacetamide (BSTFA) +1 % trimethylchlorosilane (TMCS) for 1 h at 80 • C. Details regarding the GC instrumental parameters are presented elsewhere Parinos et al, 2013).…”

Polycyclic Aromatic Hydrocarbon Degradation and Sorption Parameters in Coastal and Open-Sea Sediment

“…Due to their toxicity to humans, mutagenicity and carcinogenicity, 16 PAHs are included in the US Environmental Protection Agency (EPA) priority pollutant list (Laflamme and Hites 1978;Keith and Telliard 1979;Neff 1979;Elmquist et al 2007;Honda et al 2007;Parinos et al 2013). These organic compounds are found in all environments.…”

“…Aqueous-phase PAHs are more available and therefore have a greater toxic potential, than solid-phase PAHs. Owing to their highly hydrophobic nature, PAHs show strong sorption to sediment organic matter and to fine combustion particles (like soot and/or char black carbon), which protect them from degradation during transport in water (Dachs et al 2002;Yunker et al 2002;Ravaioli et al 2003;Neff et al 2005;Parinos et al 2013). The partitioning of organic compounds into solid and aqueous phase can be expressed by the distribution coefficient (K d ), a physicochemical parameter describing the ratio of solid phase (C s , ng g −1 d.w.) to aqueous phase (C w , ng ml −1 ), where C is the concentration of the contaminant (Karickhoff et al 1979;Trevisan et al 1995;Yu et al 2009).…”