Tributylin Antifoulants and Dogwhelk Imposex
Anti-fouling Paint on Boats Makes Female Dogwhelks Sterile
Jan 17, 2009
Marine antifouling paints harm the environment.
TBT compounds are effective in preventing the fouling of boat hulls, but they are toxic.
Molluscs and Barnacles on Boat Hulls
Wooden boats can be damaged by burrowing molluscs (shipworm), and all materials used in the construction of modern ships will become ‘fouled’ with growths of barnacle, molluscs and algae over time. These unwanted additions to the smooth surface of the hull slow the craft down and make it unresponsive when manoeuvering. It is common practice to paint the hull with special ‘anti-fouling’ preparations containing various tributyltin compounds.
Tributyltin Toxicity
- TBT compounds are toxic chemicals which harm humans and environment, and they are persistent organic pollutants that bioconcentrate up the food chain. Tributyltin has been linked to obesity in humans, and it causes ‘imposex’ in dogwhelks. Female Dogwhelks (Nucella lapillus) have an unusual reaction to these compounds – they grow a structure equivalent to the male penis. This effectively renders them infertile, and populations near boatyards are declining.
- Tributyltin compounds last a long time in the marine environment, and the Chronicle Herald in Nova Scotia reported (29 September 2007) that female dogwhelks around Halifax were still growing penises, even after the use of TBT had been banned in the area.
- There is also concern about the toxicity of TBT to marine mammals. Dead sea otters and stranded bottlenose dolphins sometimes have high levels of tributyltin in their livers. (TBTs are immunosuppressants, so they can allow damaging infections to develop.) There is the additional fear that TBTs might cause hearing loss in whales.
Biological Monitoring
- Tributyltin is not thought to pose any major hazard to humans directly, but there is no doubt about its detrimental effects on certain marine species. One of the best ways to monitor levels of TBTs in any locality might well be to survey the dogwhelks of the area. Dissecting a few and noting any reproductive system abnormalities will correlate well with levels of these compounds, and since these animals are some way up the food chain (they feed on barnacles and mussels which are both filter-feeders eating plankton) they accumulate TBTs and can indicate that small traces remain in the locality.
- This use of changes to a study animal (or the use of biological diversity as a measure of freshwater pollution) has significant advantages over measuring the precise levels of pollutants in the water at any given time. Individual animals (and communities) testify to pollution events in the recent past, and the phenomenon of bioconcentration (where animals some way up the food chain accumulate chemicals in their bodies) means that very low concentrations can be detected. The other major advantage of this type of environmental monitoring over direct analytical methods is that they are relatively cheap!
The copyright of the article Tributylin Antifoulants and Dogwhelk Imposex in Marine Conservation is owned by John Blatchford. Permission to republish Tributylin Antifoulants and Dogwhelk Imposex in print or online must be granted by the author in writing.
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