PAHs and n-alkanes in Mediterranean coastal marine sediments: aquaculture as a significant point source.

The occurrence of polycyclic aromatic and aliphatic hydrocarbons in fish feed, sediment trap material and marine sediments was examined at two fish farms in the eastern Mediterranean. The average (min-max) concentrations of polycyclic aromatic hydrocarbons (PAHs) in fish feed and particulate effluents were 316 (287-351) ng g(-1) DW and 487 (475-499) ng g(-1) DW, respectively. Lower PAH levels were determined in the underlying marine sediments. In the surface sediments under the farms (0 m distance from the edge of the cages) and in the immediate vicinity, the concentration levels of n-alkanes and PAHs were significantly higher than in the surrounding sediments in both sites. PAHs and n-alkanes individual component profiles of fish feed and sinking material were similar with the corresponding profiles of the sediment samples collected in the immediate vicinity around the cages. On a daily basis, the average PAH sedimentation fluxes under the cages was 24.4 microg m(-2) d(-1), which is considerably higher compared with the observed PAH sedimentary fluxes in the open eastern Mediterranean. Our results imply that fish farming is a significant source of these persistent organic pollutants (POPs) in the marine environment and therefore a likely change in the scale of production might introduce new sources of environmental risk. Further work is required in order to develop an appropriate monitoring system for the sustainable development of the aquaculture sector.