Researchers at Curtin University have claimed that the molluscs off the coast of Perth have contracted imposex - the development of a second sex organ - after waters were contaminated with the chemical.
Local Department of Environment and Agriculture associate professor Monique Gagnon said that TBT levels have declined at sites visited by recreational boats, but noted that 100% rates of imposex in snails are still observed at areas hosting commercial vessels, AAP reports.
Gagnon said: "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 added that according to her studies, during which snails were collected between March and June 2009, the Garden Island naval facility and Fremantle port were the main sites suffering from TBT contamination.
The existence of imposex snails may prevent the females from procreating and reduce their numbers.
Although common garden snails are hermaphroditic, the Thais orbita marine species has distinct sexes.