Release of dissolved trace metals and organic contaminants during deep water disposal of contaminated sediments from Oslo harbour, Norway

Purpose The current study was conducted in order to assess the release of dissolved contaminants from sediment relocation works in Oslo harbour, Norway, whilst operations were being carried out, and to assess the potential for spreading into the wider fjord area. Materials and methods This was achieved by comparing the concentration of metals and organic contaminants in the vicinity of the disposal site, and at strategic locations in the adjacent fjord area. In total, 14 stations were chosen, with passive sampling devices, diffusive gradients in thin films for metals and semipermeable membrane devices for organic compounds, deployed at various depths at each station for a period of 1 month. Results and discussion The highest concentrations were generally found closer to the harbour area where trace metals and organic contaminants are supplied from several sources including river discharges and old, contaminated sediments. Near the deposition site, the concentrations of polychlorinated biphenyls were low and the concentration gradients for Cd, Zn and Cu indicated removal of these metals from the water column, probably due to association with sulphides present at the deposition site or in the discharged sediments. Elevated concentrations of Pb and polycyclic aromatic hydrocarbons (PAHs) revealed that the disposal acted as a source of these compounds, but maximum concentrations were similar to or less than those predicted before the deposition begun. The estimated vertical transport and spreading to areas outside of the semi-enclosed sill basin was negligible. Conclusions Strictly, the validity of the results presented here are limited to a 1-month period of the disposal operations which lasted nearly 3 years. During this period, release of contaminants was compound-specific, but even for the most labile PAHs and Pb, the release appeared to be in the same order of magnitude or smaller than the release from other local sources not limited in time to the duration of the remediation operation.