Analysis and prediction of the dynamics of Polycyclic aromatic hydrocarbons in the coastal environment polluted by heavy oil.

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The concentration of polycyclic aromatic hydrocarbons (PAHs) in the coastal sands and other media of a heavily polluted site of the Nakhodka oil spill were found to be as low as the background after the 7 years of the accident. Oil residues were found only in the hollows and cavities of the rocks, and PAH contents in those residues decreased to one thirds of the original value in two years, but after that, PAHs contents remained at the same level, suggesting that PAHs will remain long as oil residues.Two years of monitoring of PAHs in the river water, SS and sediments revealed that the main sorbent of the PAHs in the sediments was organic matter. Organic matter based partition coefficient Koc was found to be well correlated to octanol-water partition coeffient, and can be described by using liner free-energy assumption.The exchange of PAHs between surface sediments and river water was sufficiently fast for allowing us to consider that the partition between the sediments and water is approximately in equilibrium.In the laboratory experiments, we investigated the effect of dissolved organic matter (DOM) on the partition of PAHs between sediments and water, and found that as the number of aromatic rings increases, the effect of DOM increases, and also found that for the precise description of the phenomena, we have to take into account the adsorption of DOM to the sediment particles.As described above, in the coastal environment, exchange between water and coastal particulate media is sufficiently fast to remove the pollutants from the polluted sites in several years, and at the mouth of the river, that is so fast that we can assume an approximate equilibrium. Sorption of PAHs to particulate matter is mainly to organic matter, and the partition coefficient is larger as the number of aromatic rings increases, and can be roughly estimated by using linear free energy assumptions.