Harmful substances

Harmful substances are the toxic substances that reach the North Sea from the land, specifically via rivers or which come straight into the sea. Substances entering the water from the atmosphere, activities at sea and discharges from ships also contribute to this. Clearly for Belgium the Scheldt, with an average flow rate of 104 m³/s, is the main source of contaminants to reach the North Sea via the rivers. Belgium does not produce any direct discharges – industrial or other – into the sea.

Some examples of harmful substances:

• Heavy metals: A recent inventory of the input of harmful substances in the 'North Sea Quality Status Report 2000' produced by the OSPAR Commission indicates that the concentrations and input of the heavy metals cadmium, mercury and lead in the North Sea are declining.
• TBT: Tributyltin, an antifouling substance that prevents the growth of organisms on ship's hulls, is found in large quantities in ports and along shipping lanes. The impact of TBT can be seen mainly in sea snails, in which TBT causes hormonal problems with the result that female snails develop male characteristics (imposex) and reproduction is threatened. The use of paint containing TBT has been banned on hulls smaller than 25m since 1990. On 1st October 2001, the “International Convention on Control of Harmful Anti-fouling systems on ships” was adopted after a diplomatic conference of 5 days in London. This convention prohibits the use of TBT worldwide from 1st January 2003. From 1st January 2008 all TBT has to be removed from all ship hulls. The convention will enter into force when 25 countries, representing 25% of the merchant navy, have ratified it. In addition, the European Union issued the directive EG/2002/62 of 09.07.02 that prohibits the member states to put TBT on the market. Another law is in preparation to prohibit the presence of TBT on ships in the member states.
• PCB's: Although the input of PCBs, another disquieting organic substance, occurred mainly prior to 1980, only a relatively small reduction in concentrations may be observed in the North Sea. This may be attributed above all to the very persistent nature of PCBs. DDT, the use of which has been banned in Europe for decades, is still found in large concentrations in certain places.