Tributyltin (TBT) is an aggressive biocide that has been used in anti-fouling ship paints since the 1970s. The toxicity of TBT prevents the growth of algae, barnacles and other marine organisms on ship hulls. However, TBT leaches from the paint and enters the marine environment. TBT accumulates in sediments, especially in areas with a high density of ship movements such as harbours and ports. From 1 January 2003, the use of TBT in anti-fouling systems on ships was banned, following a decision taken by the International Maritime Organisation (IMO) and Commission Directive 2002/62/EC of 9 July 2002 on organostannic compounds. In order to prevent desorption from sediments reintroducing TBT into the marine environment, effective removal and treatment methods for TBT contaminated sediments need to be implemented. This project aims at demonstrating an integrated approach to eliminating TBT from the marine environment that includes prevention, removal, treatment and finally reuse.
The overall objectives of the project was to provide an integrated solution for the permanent removal of TBT from waterways near harbours and inland ship repair yards. Specific objectives included the following:
- assess the environmental impact of TBT alternatives already available;
evaluate TBT release from sediments to aquatic environments during dredging operations;
test on a pilot-scale several treatment technologies for TBT contaminated sediments;
identify possibilities for reuse of treated sediments.
The following are the expectred results to be obtained:
- a list of environmentally friendly alternatives to TBT in anti-fouling systems;
- the presentation of dredging conditions minimizing TBT release from sediments;
- an integrated treatment technology for TBT contaminated sediments, according to the BATNEEC principle;
- re-use possibilities for treated sediments.
Comprehensive evaluation was provided regarding the different existing alternatives for anti-fouling paints containing TBT. For each of these alternatives the environmental impact is discussed. This evaluation showed that environmental friendly anti-fouling paints exist and are under development. Another conclusion of the TBT Clean Project is that the extent of TBT release during dredging activities is mainly determined by local harbour conditions (pH, T° and salinity). Environmental conditions during dredging are more important than the dredging technique. Therefore, dredging of highly-contaminated sediments in the Port of Antwerp should be performed during winter time and when pH of the water is below 8.0. A new dredging time schedule now dramatically diminishes TBT release in the docks. A recommendation could be given to other ports that dredging activities in areas with high TBT concentrations be limited to certain periods. The reference scenario in Flanders and many other (European) regions for dredged TBT contaminated sediments is de-watering and dumping in landfills, which cannot be seen as a sustainable solution.
The evaluation of the different treatment techniques and the cost-benefit analysis showed that there exist other environmental friendly alternatives that are able to cope with the TBT contamination. Especially, bio-remediation and thermal treatment are seen as promising techniques. Given that there was no standard for the re-use or application of sediment on land, geo-technical and chemical requirements were developed. Chemical criteria were developed by VITO, the Flemish Institute for Technological Research, in accordance with Flemish legislation on re-use of soil and treated mineral waste for construction purposes.
The study can be considered as a general framework to be used to quantify effects on organisms, health, and environment. The project results can also be used to fix limits and standards for reuse of sediments in different conditions. For the port authorities, this is a good framework for discussion with Flemish authorities. It could also serve as a base for development of a European regulatory framework for quality assessment as regards organization in sediments with respect to their reuse on land.
Following an ex-post follow-up report carried out by the LIFE external monitoring team in March 2005, it was learnt that the Port Authority has decided to undertake further study into building a mechanical water extraction installation at an estimated cost of EUR 65 million. The installation, Amoras, from the Dutch for ‘Antwerp mechanical water extraction and sludge recycling and utilisation’, should be operational by the end of 2008. The project for mechanical de-watering of dredged material is carried out in consultation with the Flemish Government. When evaluating suitable treatment techniques, the outcome of the TBT Clean project will be taken into consideration. If legislation will allow recycled sediments to be reused for dykes, then prospects will be very encouraging for the Port of Antwerp considering the limited number, cost and size of dumping sites in Antwerp.