Monocyclic aromatic hydrocarbons (phthalates and BTEX) and aliphatic components in the SE Mediterranean costal Sea-surface microlayer (SML): Origins and phase distribution analysis

• Published in: Marine chemistry Vol. 205; pp. 56 - 69
• Main Author: Astrahan, Peleg
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 20.09.2018
• ISSN: 0304-4203; 1872-7581
• DOI: 10.1016/j.marchem.2018.07.009

Coastal waters are subject to many sources of organic matter, such as land runoff, industrial and urban waste, rivers and atmospheric depositions. Semi-volatile organic compounds (SVOC) are frequently found next to coastal and urban areas. Depending on the specific physical properties of each compound in the SVOC group, these compounds may be adsorbed to particulate matter, evaporate to the atmosphere or accumulate in the sea's uppermost layer - the Sea surface microlayer (SML). Since many of these compounds present health risks, understanding the mechanisms that control the SVOC environmental concentration is crucial, especially in coastal waters. This study assesses for the first time, the origin of monocyclic aromatic hydrocarbons (MAH) and aliphatic SVOC, as well as their distribution pattern in the SML and the sea sub surface layer (SSL) of the Haifa (Israel) coastal waters during 2015. Seasonal analysis of the SML and SSL showed high prevalence of several SVOC members, including BTEX, phthalates, trimethyl-benzene and monoterpenes. Concentrations of the BTEX group were elevated in the SSL particulate (>0.2 μm) and the SML free fractions (<0.2 μm), while only minor to nil levels were found in the SSL free fraction. Total phthalates were recorded in all sea layers, yet were found in higher concentrations in the SML's particulate and free fractions. The distribution of these molecules was linked to the presence of SML polysaccharides that showed elevated concentrations in the rainy season. Phthalates are rapidly transported to the SML in this area and have the potential of either aggregating or dissolving in the water column. We conclude that when examining the dominant MAH distribution, low-molecular weight phthalates enrichment takes place in the SML despite their higher solubility compared to the BTEX group. BTEX molecules have potentially elevated emission rates from SML particulate matter, with low adsorption to particulate matter and very low water solubility in the SSL. These observations may be linked to the low affinity of BTEX molecules to local particulate matter and to the low Henry coefficient (KH). Molecules like low-molecular weight phthalates (higher KH than BTEX), can be found in all water layers, but tend to concentrate in the SML and may also become airborne (though to a lower extent in the gas phase) via aerosol forming processes. Finally, while atmospheric depositions were found to be the major source of BTEX components in 2015, phthalates originated from urban runoff, the Kishon River as well as atmospheric depositions. These results may explain the long term presence of phthalates in aqueous form and the chronic BTEX evaporation in this coastal area. •Phthalates concentrated in the particulate and free forms at the SML of Haifa coast.•BTEX and similar molecules concentrated in the free form at the SML and in the particulate form at the SSL of Haifa coast.•Elevated levels of BTEX and extreme concentrations of phthalates were recorded in aerosol particles, loading the SML.•Airborne particles might load the SML with monocyclic aromatic molecules.•Urban runoff reaching Haifa's coastline, supply high concentrations of organic matter including extreme levels of phthalates.•Slicks formed following urban drainage water discharge, included high levels of polysaccharides and extreme levels of phthalates in crude SML samples.