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TBT Ban Lets Girl Snails Be Girls

Thursday, January 16, 2014

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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.

TBT snail imposex
Curtin University via

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.

Exploding Snails

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.

'Horrifying' Discovery

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.

antifouling coatings
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.

Slow Recovery

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.


Tagged categories: Coating Materials; Construction chemicals; Environmental Control; Environmental Protection; IMO; Marine Coatings; Research; Shipyards

Comment from Catherine Brooks, (1/16/2014, 11:26 AM)

Great 'eye-catching" title. My chuckle for the day... but it does show the commonly- undetected side effects of the millions of products we create to help us but damage other things.

Comment from Joni McGinnis, (1/16/2014, 1:40 PM)

I love this comment by Matthiessen "The idea of a female snail growing a penis was a dramatic discovery, and quite a horrifying one at that"

Comment from Marco Hanquart, (1/17/2014, 4:13 AM)

And for sure copper based paints will be next on the list to be banned, and rightfully so.

Comment from Tony Rangus, (1/17/2014, 9:16 AM)

Forget the damn snails, what about the thousands of poor aaplicator personnel, especially those who were applying coatings in the 1960's & 1970's when controls were lax. I doubt there are any applicators with a penis or an extra penis growing somewhere on their body, but what the hell else did TBT alter or modify? Not only horrifying but quite disturbing, and I thought washing your hands in xylene was bad.

Comment from Jeff Longmore, (1/17/2014, 9:21 AM)

When TBT antifoulings were being vigorously promoted back in the 70's we sincerely believed they were the "silver bullet" of active ingredients. Conventional wisdom knew that the tributyltin rapidly became dibutyltin which then rapidly decomposed to inorganic tin at background level concentrations. The knowledge that TBT strongly adsorbs onto silt and mud and then stays stable and toxic came much later.

Comment from M. Halliwell, (1/17/2014, 11:04 AM)

Jeff, that sounds a bit like asbestos. It was fireproof, flexible, strong, could be woven into fabrics or mixed into concrete, didn't react with most chemicals, noise many great properties for so many applications! Then we found out that it caused lung cancer, asbestosis and mesothelioma.

Comment from Dan Chute, (1/17/2014, 12:05 PM)

While "rules are rules" and none of us will be applying TBT any more (as I did in the 80's), don't confuse theories with proven facts. Scientists acknowledge that the "imposex" feature was observed long before TBT was ever used and many species of gastropods can't form such features even when exposed to TBT in laboratories (O'Neill,,J.Environ.Monit. Sept 2011). Further, how such features occur is not understood, so no one can demonstrate any source of causation (Reis-Henriques,, Aquat.Toxicol., Jan 2011). Bottom line is we have an equivalent amount of "proof" that these headlight features are caused by saltwater. Of course you can get more jobsite giggles and research grants with the original potty-humor theory.

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