Crude oil enters into water through accidents or also routine activity. What are the crude oil concentrations (ppm or mg L-1) in the different water layers directly after oil enters into water? I have read a lot of papers on this topic and I cannot find any concrete numbers on the realistic concentrations of water in oil spill conditions.
The reason you cannot find definitive answers to the question is becsuse some many factors are at play. The nature if the spilled oil is important including viscosity (propensity to flow andxspread), specific gravity (mass and density), chemical composition (fractions and propensity to dissolve) and others. Nexy is the nature of the receiving water such as its ionic content (salt vs fresh), temperature, energy (wind, waves, currents, and surface motion and rougness), light exposure (sunlight changes oil temp and uv helps chemical change). Finally there are the changes in the oil collectively called weathering through which the oil moves, spreads, dissolves, evaporates, reacts, sinks, mechanically disperses, or emulsifies (water is entrained in the oil), etc. So depending on the oil, the environment and weathering you can get different presentations of oil on the water surface, such as pools and patches, windrows and streamers, surface and sub-surface floating. Sheens can be very thin - between 0.05 and 50 microns thick (but still over three orders of magnitude) and "thicker" slicks that maintain their original colour when viewed from above can be 50 to 200 microns or more thick. Note 200 microns us still 0.2mm thick. So thicker slicks that have undertaken spreading and other wrsthering tend to be partially emulsified making it higher viscosity (thicker in both senses).
All of this is well explained in the ITOPF website at:
http://www.itopf.com/knowledge-resources/documents-guides/fate-of-oil-spills/weathering/
Thank you a lot. Here I need to get more concrete: As I have read a lot of papers describing the emulsification and dispersion process, non of them are talking about the amounts, eg is there a 10 or 1000 ppm of crude oil in the water. As it appears from toxicologic studies, the realistic concentratsions are consideres as 40 ppm, but can I say that 1000 or even 2000 ppm is sometimes realistic, eg when the emulsification of crude oil is taking place?
Lennart. You can make no assumptions about the total petroleum hydrocarbon (TPH) concentration in the water, as it depends on the factors i mentioned above, plus local mixing and dilution. The only way to do it is to actually measure it and recognise that whatever you measure is an instantaneous result, that will have no relevence spatially or temporally, unless you continue to monitor and measure over time and space.
Sorry, but desite some real garbage in the international literture, you cannot make assumptions about concentrations, as some fractions of the crude oil are more soluble and more toxic than others, depending on the oil composition and state of weathering.
You could try some simple calculations. Start with a 200 micron thick slick. At the surface - this represents around 200ml per square meter. Under even the most benign energy conditions this oil should mix down to at least one meter. Assuming full dilution this represents 200ml in 1,000,000ml or 200ppm. No oil dissolves or dilutes completely, and the dilution zone is always more than 1m deep. So whilst there may be a graduation zone concentrations of 1000s ppm seem unlikely in a real world situation.
Emulsified oil tends to increase significantly in viscosity and this will likely lower the transfer of volatile (more toxic) components into the water column, so it would be very special circumstances where 1000sppm would arise.
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