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FEMALE marine snails living off the Perth coast are growing male sex organs on their heads after exposure to the chemical TBT, according to local researchers. Curtin University researchers have revealed the snails are suffering from imposex, a condition that involves the development of a second sex organ after being exposed to the chemical. Unlike garden snails, which are hermaphrodites, this species of marine snail has distinct sexes. Curtin's Department of Environment and Agriculture Associate Professor Monique Gagnon said studies on the marine snail Thais orbita over the past 10 years showed that although TBT contamination had declined at sites visited by recreational boats, a 100 per cent rate of imposex still existed at sites where commercial vessels were present. “These high levels are believed to be related to the continuous input of TBT into the area over a period of years, resulting in the presence of significant quantities in the sediment on the sea floor,” she said. Associate Professor Gagnon said Fremantle port and the Garden Island naval facility were the main sites where TBT contamination was present in the Perth region. She said studies had shown that imposex could stop the females from procreating, potentially reducing the number of snails in the shoreline environment. The samples of Thais orbita were collected along the Perth coast between March and June 2009. added by: eden49