SHELLFISH in the North Sea have recovered dramatically since small boats were
banned from using antifouling paints containing tributyltin (TBT). But a British
scientist warns that extending the ban to large vessels could do more harm than
good.
Antifouling paints are applied to the hulls of boats to kill barnacles.
Countries bordering the North Sea banned the use of TBT paints on small boats
during the 1980s after marine biologists revealed that tiny amounts of the
chemical dissolving into seawater can damage marine molluscs. Problems include
sterility and a condition called imposex, in which females grow a rudimentary
penis. The damage was worst around marinas, harbours and estuaries.
By the mid-1990s, with TBT still in use for larger ships, imposex was taking
hold in the North Sea and some scientists were forecasting that whelks would
become extinct there unless there was a total ban. Last year, the UN鈥檚
International Maritime Organization agreed to ban the use of TBT on commercial
shipping worldwide.
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But now researchers at the Dove Marine Laboratory at the University of
Newcastle upon Tyne report a revival of North Sea whelks. The number of whelks
landed at fishing ports tripled between 1992 and 1997. Andy Birchenough told a
meeting of North Sea researchers at the university last month that they are now
abundant on the coasts of Britain, Norway and France.
鈥淪ymptoms of imposex have decreased dramatically,鈥� says Stewart Evans, the
laboratory鈥檚 director. He agrees that the main cause of the revival was the TBT
ban. But he opposes its extension. 鈥淚t should wait until we have done sufficient
research to know that the alternatives won鈥檛 do even more environmental harm,鈥�
he says.
One leading alternative, Irgarol 1051, made by the Swiss-based chemicals
company Ciba, is widely found today in European coastal waters, and 鈥渁lready
appears to be causing harm鈥�, says Evans. 鈥淥ff the west coast of Sweden it is
associated with the death of phytoplankton.鈥� But Ciba says its studies suggest
the chemical doesn鈥檛 persist in the environment. Other alternatives contain
copper, which can also be toxic to marine life at high concentrations.
Evans sees some benefits from sticking with TBT for large ships as it is
still the most effective antifoulant. And he thinks fouled ship hulls may carry
alien species into new habitats. 鈥淚reland never had any invasions of marine
species until they stopped using TBT,鈥� he says.
But many environmentalists disagree. Sian Pullen, marine expert with the
British arm of the Worldwide Fund for Nature, says: 鈥淭his is no longer just
about molluscs. TBT and its breakdown products dibutyl- and monobutyltin are
getting into the food chain.鈥� She says that the problems of alternatives are
overstated. 鈥淭here is good evidence now that copper-based paints do not invade
the food chain anything like as much as TBT.鈥�