Gastropods

Ship barnacle killer bends snail genders

PUBLISHED : Friday, 21 July, 1995, 12:00am
UPDATED : Friday, 21 July, 1995, 12:00am

LONELY female snails are wandering the shores of Hong Kong unable to find mates because of a gender-bending chemical which has made them grow penises.


Tributyl tin, or TBT as it is also known, is a powerful pesticide which is mixed into ship paint to stop barnacle growth. It is used on practically every ocean-going vessel which passes through Hong Kong waters.


But TBT, even in the tiniest quantities, can cause the onset of 'omposex' - a condition which turn females into infertile males.


The chemical is so powerful that as little as four teaspoonfuls would be needed to contaminate Causeway Bay. TBT leaks out of ship paint once it has been applied, polluting the sea for as long as it is on the vessel.


'TBT is present throughout Hong Kong waters and is having a devastating effect on the snails,' Swire Institute of Marine Science director, Professor Brian Morton said.


'Virtually every female snail in Hong Kong has been showing symptoms. They are dying out because they are unable to breed. You can't find an adult snail any more.' British researchers found the closer female snails lived to shipping docks where TBT paint was used, the larger their penises.


When the transexual snails were painted with the chemical, researchers said 'penises sprouted and grew to alarming lengths'.


Hong Kong banned use of the chemical in 1992 on vessels under 25 metres.


But a survey by the Environmental Protection Department has found that TBT based paints are still being applied to small vessels.


As an added restriction the paint can only be sold in containers over 20 litres, to discourage use by small boat owners.


'When small craft sit in a marina, the TBT leaches out and collects in high quantities. That is why those regulations were enacted,' Malcolm Broom, of the Environmental Protection Department, said.


A researcher has been sent from the Swire Institute to Wales to study the problem and find a solution for Hong Kong.


TBT has ravaged the British coastline, wiping out most snails, whelks and dog whelks, especially in the North Sea.


Until recently it was believed that TBT did not affect mammals, but alarming research in Japan has found toxic levels in dolphins and whales.


Porpoise caught off the Japanese coast were found with levels of 36 ppb (parts per billion). But deformities in snails can be caused by levels as low as 0.02 ppb.


No safe level of the chemical has been discovered.


'The main concern is the effect it is having on the entire marine system,' Professor Morton said.


'This chemical wipes out the keystone predators and leaves nothing in their place.' The European Union is negotiating the phase-out of TBT based paints by 1997. Britain and France have banned it on boats under 25 metres. Japan has outlawed it since 1990.