Construction work for the Vuosaari harbour began in January 2003. In the spring of 2003, elevated concentrations of tributyltin (TBT) were detected in the seabed outside Vuosaari harbour. TBT is an organic tin compound, which is harmful especially for primitive marine organisms, such as molluscs. The construction work for Vuosaari harbour uncovered the TBT problem, which will now be eliminated in a safe manner. Removing the TBT from the bottom sediment will permanently improve the state of the marine environment.