Female snails burdened with penises on their heads are finally seeing some relief to their decades-long struggle with unwanted (and unusable) sex changes, thanks to—of all things—a coatings ban.
The condition (the development of non-functional male organs) is called imposex, and its appearance in generations of female marine snail populations has been blamed on the long-popular ship hull coatings that contained the chemical tributyltin (TBT).
Starting in the 1960s, TBT was widely used in antifoulings paints for ship hulls. By 1970, imposex was being reported in marine snails worldwide.
Curtin University via au.news.yahoo.com
Antifouling coatings with TBT have been blamed for worldwide populations of female marine snails growing penises out of their heads. Six years after the chemical has been widely banned in ship coatings, snail populations are now starting to recover.
It's been six years since TBT antifouling coatings were widely banned, and snails are now starting to recover from their unwanted sex changes, scientists report.
Adopted in 2001 by the International Maritime Organization, the International Convention on the Control of Harmful Anti-fouling Systems on Ships prohibits the use of TBT antifouling coatings on ships and establishes a mechanism to prevent the potential future use of other harmful substances in antifouling systems.
The Convention took effect on Sept. 17, 2008.
According to the IMO, TBT has been shown to cause deformities in oysters and sex changes in marine snails.
"For every site that we looked at in the late 1980s, there was not one that did not have snails with imposex," Dr. Scott Wilson, a marine biologist with Central Queensland University, told ABC Environment about his snail studies in Australia.
At the time, imposex was being reported in snail populations around the world. Eventually, entire snail populations disappeared in some regions, as the females were unable to reproduce with their new male parts.
In 1992, the Eugene Register-Guard ran an article about the discovery of female snails growing penises in the polluted coastal harbors of British Columbia. Although there wasn't enough research to confirm it at the time, researchers suspected TBT as the cause. In some species, the female snails not only grew a penis, but their ovaries turned into testicles, the newspaper reported.
American Coatings Association
The effects of TBT on marine life could still last for decades as the chemical continues to be released from the sediment it has settled into, scientists say.
"It was totally unexpected. Nobody in their wildest dreams would have imagined that such effects could occur and at such low concentrations, at nanograms per litre concentrations of TBT," Dr. Peter Matthiessen, an ecotoxicologist in the UK, told ABC Environment.
Matthiessen has been studying the effects of TBT on marine organisims in the UK for over 30 years.
In heavily contaminated areas, some snail populations were wiped out because the female snails "effectively exploded" since they couldn't shed their eggs, Matthiessen said.
"The idea of a female snail growing a penis was a dramatic discovery, and quite a horrifying one at that," Matthiessen said.
Wilson says that he has noticed a reduction in gender-changing snails, and in some cases no signs of imposex at all. Additionally, small snail populations are starting to crop up where they weren't previously found.
Matthiessen says his studies in the UK show similar conditions.
"In areas where the populations were wiped out, we are now beginning to see slow recovery since the complete ban kicked in in 2008," Matthiessen told ABC Environment.
It took 20 years to ban TBT once the effects were known, partially because of the time needed for enough countries to ratify it, and partially because of delays from the paint and shipping industries, Matthiessen speculates. (Apparently, no one consulted the snails.)
"There was a lot of opposition, and all sorts of arguments were deployed to avoid or at least delay a ban. The TBT story shows exquisitely how once a polluting substance is out there and once it's the basis of a huge industry, it's a devil of a job to get it banned because of all the vested interests," Matthiessen told ABC Environment.
However, by the time the U.S. ratified the treaty in 2012, both coatings manufacturers and the U.S. Environmental Protection Agency supported the move.
As of Oct. 31, 2012, 63 countries representing 81.06 percent of the world's merchant shipping tonnage have ratified the Convention, according to the National Oceanic and Atmospheric Administration.
Years to Go
But the snails' struggle could be far from over.
TBT has a half-life of six days in seawater, but it can last for years once settled into marine sediment. It could take decades for heavily contaminated harbors to release all the TBT stored in it sediment.
Based on current rates of recovery, Wilson thinks it will take until at least 2040 for the Australia area to be free of imposex.