Temporal trends and identification of the sources of volatile organic compounds in coastal seawater

Volatile Organic Compounds (VOCs) in the marine environment are produced by biogenic sources (marine macroalgae, phytoplankton, sediments, etc.) as well from anthropogenic sources. The temporal variation of such VOCs was studied together with their relationship to biological, meteorological and physico-chemical factors. Sixty four different VOCs were quantified including halogenated (< LoD to 906 ng L-1), non- methane hydrocarbons (NMHC) (< LoD to 1539 ng L-1), mono-aromatics (< LoD to 4232 ng L-1), oxygenated (< LoD to 1539 ng L-1) and sulfur containing compounds (< LoD to 160 ng L-1). The analyses were performed employing solid phase microextraction (SPME) coupled to gas chromatography/mass spectrometry (GC/MS) analysis. Pigments such as chlorophyll a correlated with halogenated compounds (e. g. chloroform and dichloromethane) and dimethylsulfide (DMS) was maximal during the spring bloom. Multivariate statistical analyses demonstrated seasonal changes in the VOC signature (more mono-aromatics and alkanes in the winter and halocarbons in the summer). Principal component analysis (PCA) demonstrated that physico-chemical and meteorological factors such as wind speed and water temperature can influence the detection of VOCs in surface waters as well their productions. Partial least squares (PLS) modelling highlighted the importance of the microalgae signature in spring while macroalgae and sediments dominated at other times. Short term variability in concentrations and fluxes was due to such factors as tidal state, wind speed and seawater temperature. The atmospheric concentrations were significantly less than any regulatory values although no measurements were made in eutrophic conditions.