Anti-fouling paints based on TBT were developed in the 1960s. The products are extremely effective, but have had widespread environmental effects. TBT concentrations as low as 5ng/l cause deformities in oysters and reproductive problems in other molluscs. In 1993, an official UK study found that dogwhelk populations in many southern areas of the North Sea had been endangered by TBT (ENDS Report 227, pp 7-8 ).
Use of TBT coatings on smaller vessels was banned in the 1980s, but remains common on ocean-going ships of over 25 metres. Manufacturers have sought to achieve equivalent performance with non-TBT formulations which can work effectively for up to five years - reducing the need for ships to be cleaned down and recoated in dry dock. In 1994, Rohm & Haas gained US approval for a thiazolone-based paint, claimed to have a 3-4 year service life (ENDS Report 232, p 30 ).
Another major manufacturer has now claimed a "breakthrough" with a copper-based alternative. Courtaulds' subsidiary International Paint says that its Ecoloflex coating matches the performance of TBT products. Developed in partnership with Nippon Paint Marine Coatings, the product has been tested extensively in Japan where TBT formulations have been banned for several years.
International Paint says that some 3,000 vessels have now been treated with Ecoloflex. The paint is based on copper acrylate and a new "rapidly degradable" biocide, the identity of which has not been released. It carries a price premium of 50% for formulations designed to last three years and 75% for five-year formulations.
The recent advances in TBT-free antifoulants is likely to encourage the International Maritime Organization's Marine Environmental Protection Committee (MEPC) to call for a total ban on TBT products. In 1996, it set up a group with the aim of developing "long-term measures (within the next ten years) moving towards a total ban of TBT paints." This has been widely interpreted as a phase-out by 2006 - but an earlier date may now be on the cards.
An MEPC spokeswoman told ENDS that the committee's viewpoint has changed markedly over the past two years and "things were definitely moving" in favour of a ban. A five-year horizon is now "likely", depending on the outcome of key meetings in March and November.
A spokesman for the International Chamber of Shipping, which represents national ship owners' associations, agreed that the coatings industry "seems to be seeing a way through the problem" and that the quoted costs were "promising".
Pressure for a TBT ban has been increased by evidence that the compound is bioaccumulating in food chains. Particularly high levels have been found in marine mammals. Japanese researchers recently reported TBT and its degradation products monobutyl and dibutyl tin in the livers of 18 species of whales, dolphins and seals from north Pacific and Asian waters.1 Total butyl tin concentrations of up to 10,000ppb (wet weight) have been measured in animals near the coasts of Japan and Florida. The authors say that the results "strongly suggest serious butyl tin contamination in the waters of developed nations."
Japanese scientists have also reported butyl tins in animals such as birds, tuna, shark, squid and turtle. The highest levels were found in coastal species, but open-ocean whales and squid and deep-sea fish and invertebrates were also affected. They have suggested that the contamination may represent a long-term "toxic threat...in the global marine ecosystem."2