High levels of toxic tributyltin (TBT) have been measured in the sea off Jätkäsaari on the southwest tip of Helsinki’s main peninsula. Jätkäsaari currently houses harbour facilities for the Port of Helsinki. In the coming years they are to move to the new Vuosaari harbour, freeing Jätkäsaari for housing construction.
TBT is contained in special paint used on the hulls of ships, which helps keep barnacles away.
The levels exceed the maximum limits set by the Ministry of the environment for TBT. The substance has accumulated at the bottom in a layer of sediment about half a metre thick. Also found were various heavy metals, such as mercury and lead.
Helsinki has planned to build a new residential neighbourhood at Jätkäsaari. According to the plan, the district would be set up on land reclaimed from the sea.
However, the sea bottom in the area has large deposits of soft clay, which would have to be dredged out and be replaced by solid earth before anything is built on it. The dredging cannot begin until the contaminated sediment layer is first peeled away.
There is an estimated 200,000 cubic metres of contaminated sea bottom, which would have to be removed and taken away for disposal.
Tributyltin has been found in many locations near Helsinki. Three years ago the substance was found in bottom sediments in waters near the harbour construction area in Vuosaari.
TBT is toxic in very small doses. It is known to be harmful for most aquatic organisms. Its effects on humans are largely unknown.
