Tuesday 10 April 2012

Occurance and distribution of hydrocarbons in the surface microlayer and subsurface water near Marseilles

A review of: Guigue, C., Tedetti, M., Giorgi, S. & Gout, M. (2011). Occurrence and distribution of hydrocarbons in the surface microlayer and subsurface water from the urban coastal marine area off Marseilles, Northwestern Mediterranean Sea. Marine Pollution Bulletin. 62 (12), 2741-2752.

Hydrocarbons are known to pose a substantial threat upon aquatic systems due to their carcinogenic, mutagenic and toxic properties. In oceanic environments, they can originate from both natural and anthropogenic sources, and have been frequently recognised to be introduced by heavy rains, aerosols, rivers, municipal/industrial effluents and surface run off. High concentrations of organic contaminants have been shown to accumulate in the sea-surface micro-layer (SML) when compared to the sub-surface layer (SSW) in various coastal environments, due to favourable conditions derived from certain characteristics such as a surfactant and hydrophobic nature along with a potential association with floatable particles, bubble scavenging and vertical diffusion mechanisms. By concentrating in the SML, its role as a functional interface could be compromised by affecting a variety of physical, biological, chemical and photochemical interactions.

Marseilles, located on the Mediterranean coast, is the second most-populated city in France and holds a pronounced significance in a variety of shipping, nautical, industrial and tourism activities. Due to its location and the character of its local economy, the adjacent coastal areas are exposed to numerous potential sources of contamination. Previous research has documented levels of hydrocarbon contamination and distribution in adjoining coastal regions; however the incidence in the direct locality of Marseilles remains unclear.

Samples taken from near-shore observation stations, sewage effluents and harbour sites were used to investigate the incidence and distribution of aliphatic (AH) and polycyclic aromatic (PAH) hydrocarbons in the SML and SSW in the coastal waters surrounding Marseille, France (North-western Mediterranean Sea). The evaluation is then extended by applying the data in relation to hydrocarbon concentrations in both dissolved and particulate phases across larger areas of the French Mediterranean coast, whilst assisting in the identification and assessment of potential sources and their impact associated with marine contamination events.

Overall, the study observed that the coastal area of Marseilles was moderately contaminated in relation to concentrations of AH and PAH when compared to other coastal environments. Nevertheless, particular SML values exhibiting toxic levels for marine biota were noted in selected harbour and treated sewage effluent sites. AHs were determined to be of anthropogenic origin in the SML, while the SSW was characterised by compounds of a mixed origin and biogenic origin. In both SML and SSW samples, PAHs were observed to predominantly be of petrogenic and mixed origins with contaminants of exclusively pyrogenic sources only exhibited in isolated examples. Furthermore, variability and spatial differences of concentration was more readily identified in the particulate phase when compared to the dissolved phase.

The investigation emphasizes the potential anthropogenic pressures acting upon the Marseilles area by suggesting that the concentrations of hydrocarbons observed in the study are likely to be as a result of high levels of shipping traffic, spillage incidents, surface run off and urban/industrial waste. Marseilles, could serve as an example of the potential impact of large coastal urbanisation upon the marine environment, by highlighting downfalls in various practices which shape the activities of a region, subsequently assisting in the development of future management programmes representing industrial/economic practices and the marine environment more equally. Additionally, the study highlights certain features with possible further research interest such as; the significance of SML enrichment factors, the independent use of particulate and dissolved phases in accordance to the particular parameter being assessed in investigations of hydrocarbon concentration and the importance of heavy rainfall on hydrocarbon concentration and distribution.

3 comments:

adam said...

Hi

So the results of this were that the surface microlayers were significantly different to the sub surface waters? Also which method for sampling were used. As my review on surface microlayers demonstrates, there are severall methods all with different pros and cons. Dependent on the method used here, the results may have been very different so the method used is important.

adam said...

Hi

So the results of this were that the surface microlayers were significantly different to the sub surface waters? Also which method for sampling were used. As my review on surface microlayers demonstrates, there are severall methods all with different pros and cons. Dependent on the method used here, the results may have been very different so the method used is important.

Jelena Kovacevic said...

Hi David,
An interesting paper, it’s important to raise awareness of the anthropogenic impacts on the marine environment that are perhaps not as obvious as a massive oil spill and therefore often overlooked, such as the effects of urbanisation on the SML and SSW. I’ve read that materials in the SML, including pollutants as well as bacteria and virus can be transferred from the sea surface to the atmosphere and other areas in wind-generated aerosols and can have detrimental effects on the new waters and the ecosystems. Moreover, it briefly explained how changing the composition of the microlayer may alter the exchange of materials between the atmosphere and the ocean, thereby affecting global climate. I wasn’t aware how potentially detrimental it could be!
Do they discuss any potential methods to manage or clear up the pollution specifically in the surface layer? Do you reckon hydrocarbon-degrading bacteria which are suggested to help clean up oil spills, as previously mentioned in some posts, would be as advantageous when focusing just on the surface layer?