Dredging of contaminated sediments

The seabed sediments of the marine areas of the cities are contaminated in many areas as a result of industrial activity. In recent years the most harmful and most usual polluting compounds have proved to be organotin compounds, the most common of which is tributyl tin (TBT), which has been used in painting the hulls of ships and boats.

In several dredging areas the concentrations of hazardous substances in the sediments have been so high that these cannot be dumped at sea, but the sediment has to be dumped in special disposal areas that will be constructed in such a way that the hazardous substances cannot enter the marine environment. The contaminated sediments on the seabed can also harm the environment as a result of other actions. The wake from ships propellers and river dynamics can cause the sediment to drift, causing the hazardous substances to enter the water and the living organisms that are there.

For this reason, the worst polluted dredging areas, other than those in connection with harbour or fairway construction, should be included in the scope of remediation dredging, as the benefits from
remediation are significantly greater than the harm caused by the work.

Areas suitable for the disposal of contaminated sediments should be established through cooperation
between the municipalities and the state. This would give areas better suited for disposal than at present, also for actors other than the city harbours.


Helsinki and Turku...

• Dredging to remediate the areas of worst pollution by organotin compounds or other hazardous substances.
• In Helsinki the worst problem areas are off the West Harbour and Sörnäinen Harbour, and in certain places at Kruunuvuorenselkä, In Turku in the Aurajoki river estuary.
• The cities work in cooperation with other actors for the establishment of treatment and disposal areas for contaminated sediment, and the development of treatment methods.