Distribution of polycyclic aromatic hydrocarbons in the sea water column

The most intensive traffic in the world is going in the Baltic Sea. Consequences of intensive navigation are illegal or accidental oil spills. Following a spill, the soluble fraction of polycyclic aromatic hydrocarbons (PAH) is rapidly released into the water column. These remain dissolved in seawater over an extended period of time, even should the insoluble fraction be removed. Therefore, it is necessary to know how fast and what polycyclic aromatic hydrocarbons start releasing from the film of spilled oil. During an experiment, it was aimed to determine maximal concentrations of that. PAH were analysed in the dissolved and suspended phases in the water column. The study was undertaken under controlled conditions so as to minimize the variability of environmental factors such as temperature and hydrodynamics. After two weeks of the experiment, the following low-molecular weight hydrocarbons were detected: naphthalene (Naph), phenanthrene (Phe) and anthracene (Antr). No high-molecular weight hydrocarbons were detected within the total time of the experiment (8 weeks). The distributions of PAHs were measured in the dissolved and suspended phases, where total concentration of PAHs ranged from 19.01 ng L-1 to 194.70 ng L-1 in the dissolved phase and from 5.14 to 63.92 ng L–1 in the suspended phase. The release of PAHs from the film started immediately after the spill reaching 194.70 ng L-1 in the dissolved phase and 63.92 ng L-1 in the suspended phase near the bottom of water column after 1 – 2 hours. In the dissolved phase, 2 – 3 ring PAHs dominated (60 – 80 %), whereas the highest amount of 4 – 6 ring PAHs (55 – 90 %) was found in the suspended phase.