Female marine snails living off Perth beaches have developed male sex organs on their foreheads as a result of exposure to the banned toxin tributyltin, a Curtin University study has found.
The study found alarming rates of the abnormality known as imposex in the molluscs.
In waters off Cockburn Sound, Fremantle, Garden Island and Hillarys the number of females affected by the hormone disrupting disorder ranged from 50 per cent at North Mole to 100 per cent at Colpoys Point off Garden Island.
At Cottesloe the numbers were 35 per cent and Hillarys 82 per cent.
Associate professor Monique Gagnon from Curtin University said the snails had almost disappeared from Fremantle waters due to the high rates of TBT pollution and the impact it was having on snail reproduction.
She said that unlike common garden snails, which could exhibit both sexes in the one individual, the marine snail species studied in the survey had distinct sexes.
The survey was conducted in 2009 and a follow-up study is scheduled for early next year. Associate professor Gagnon said the next study could be expected to show any contamination resulting from the disturbance of the sediments from this year's dredging of Fremantle Harbour.
"Studies have shown that imposex might stop the affected females from procreating, potentially reducing the numbers of snails in the shoreline environment. Because this species is a predatory snail, a reduced population of these animals can translate into an altered biodiversity in the rocky shorelines," associate professor Gagnon said.
TBT has been banned in Australia since 2008 but some commercial vessels still dock at Fremantle Port carrying the toxin in the antifouling that protects their hulls from marine growth.
Even tiny, almost undetectable, amounts of TBT can cause female snails to grow male sex organs.
"TBT's ability to persist in sediment suggests that the legacy of environmental degradation left by its use may continue to affect marine ecosystems around Perth into the future," Associate Professor Gagnon said.
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