The prohibited paints can persist on the boats. Boat wash stations are an alternative to toxic antifouling paints and work in about the same way as car washes, with large brushes removing unwanted marine fouling organisms that reduce the speed of the boat. Since boats have traditionally been treated with paints that leach toxic substances as protection against fouling organisms, the boat wash stations are equipped with sumps for the flakes of paint removed by the brushes.
Boat wash stations are now used in several places, mainly in the Stockholm area. The Foundation Keep Sweden Clean has initiated several boat wash stations, for instance one in Trosa harbour in 2005 and another in Käppala harbour on Lidingö in 2008. By commission of Keep Sweden Clean and Trosa Municipality, the Department of Applied Environmental Sciences, ITM, at Stockholm University has made measurements of the toxic substances from antifouling paints in the sumps underneath these boat wash stations.
High TBT contents
Tributyltin is a very toxic compound that harms many organisms even in very low concentrations. It has been prohibited for 20 years for leisure boats and today it is also prohibited for large ships on a global scale.
- In the sediment from the sumps, concentrations of ca 50,000 microgram TBT/kg of dry sediment were found. Concentrations of 100 are considered very high in a lot of countries. In Sweden there is no threshold limit value. The threshold limit value proposed by EU for a safe environment is 0.02 microgram TBT/kg of dry sediment, says Britta Eklund, researcher at ITM, Stockholm University.
People who wash their boats in a wash station have often not painted their boats at all before putting them into the water for the year. The TBT found can thus come from old underlying layers of paint.