The use of TBT anti-fouling paints on boats less than 25 metres in length was banned in the UK in 1987, and similar measures have been taken in many European countries, Japan and the USA. The controls were introduced after it was found that TBT leaching from hulls was causing adverse effects in commercial oyster fisheries and other organisms, notably the dogwhelk.
In December, Ministers from the North Sea states called for further curbs or even a ban on TBT. They were responding to scientific findings that dogwhelk populations in parts of the southern North Sea are still suffering severe effects attributable to TBT exposure (ENDS Report 227, pp 7-8 ).
In March, the issue was discussed at a meeting of the International Maritime Organization's Marine Environment Protection Committee (MEPC). The outcome was not altogether conclusive - there was no recommendation for the matter to be taken up by the IMO itself - but lends support to national action on TBT.
A paper from CEFIC, the European chemical industry federation, summarised the results of recent TBT monitoring activities. These have shown that the curbs on TBT use on small craft have generally succeeded in reducing concentrations of the chemical significantly in and around small harbours.
The picture is less reassuring in commercial ports and harbours, particularly those where dry docking and ship repair are carried out.
One industry-funded study looked at TBT levels in and around four European ports - Milford Haven, Bremerhaven, Rotterdam and Genova. The lowest annual median TBT concentrations, 5-9ng/l over three years, were found in Milford Haven, which is used by a limited number of oil tankers and has little docking activity. But levels in the other three ports were one or two orders of magnitude higher, with a peak value of 340ng/l in Bremerhaven in 1991/2. These values compare with the official UK environmental quality standard (EQS) of 2ng/l.
Median TBT levels declined away from all four ports, falling to 4-32ng/l in the estuary mouths, and to 2-11ng/l on the adjacent coasts. These values, though, are still above the UK's EQS - although it should be noted that contamination problems with the analytical procedure used affected the results.
The conclusions drawn by CEFIC were that analytical methods for TBT need to be improved at international level, while an effective way of reducing TBT inputs to the aquatic environment would be to curb releases from paint stripping and application operations in dry docks.
However, the meeting heard calls from the UK for further restrictions on TBT on the back of a study carried out for the Department of Transport by Lloyd's Register.
A major issue in this study was the performance of alternatives to TBT coatings. TBT producers claim that the superior performance of their products saves the shipping industry $2.7 billion per year in lower fuel, maintenance and dry docking costs - and also reduces emissions of carbon dioxide from the world's shipping fleet by 22 million tonnes per year.
Lloyd's Register reviewed the products of all the main coating manufacturers, and concluded that the performance gap between TBT-based and modern TBT-free coatings has narrowed recently to the point that the latter are now satisfactory for service lives of up to three years. However, it was unable to validate claims that they perform as well over 4-5 years, and concluded that the costs of a TBT ban to the shipping industry, while declining, would probably remain substantial.
However, the UK proposed that TBT use could now be restricted to large ocean-going vessels - and that a ban on its use on vessels less than 50 metres in length and on ships trading primarily in coastal waters should be considered. The UK also proposed a ban on TBT coatings which do not give a controlled release of TBT, as do modern self-polishing paints. Its proposals were supported by Germany.
The MEPC responded by handing the problem back to national governments. It urged them to take steps to reduce TBT use on smaller ships and those operating in coastal waters; to co-operate in developing improved analytical procedures; to ban paints with a high TBT leaching rate; and to control TBT releases from docks. It remains to be seen whether the UK or Germany will pursue the issue at EC level.