MBA research demonstrating how toxic anti-fouling paints used on boats resulted in population crashes of marine snails led to worldwide bans on their use.

MBA research has demonstrated that tributyltin (TBT) is one of the most toxic and potent endocrine disrupting chemicals to be introduced into the marine environment and illustrates a unique example of pollution-induced cause and effect. The rise and fall of the organotin ‘problem’, stemming from the use of TBT as biocides in antifouling preparations on ships, yachts and other marine structures, has been charted for more than three decades by a group of MBA staff including Drs Geoff Bryan, Peter Gibbs, Bill Langston and Nick Pope, and supported by numerous visitors and research assistants.

In the 1980s it was noticed by MBA researchers studying marine organisms on Plymouth coasts that many populations of dogwhelk Nucella lapillus near harbours or marinas were becoming locally extinct. Detailed investigations revealed that female dogwhelks were undergoing imposex, the superimposition of male sex characteristics (penis and vas deferens development) on females (Fig. A). It was found that this ‘sex change’ was initiated in dogwhelks by extremely low TBT concentrations (Bryan et al., 1986, 1987). Severe expression prevents egg-laying and causes the death of affected females leading to population crashes.

Initial results from the field, supported by laboratory experiments to establish causality, led the UK government to restrict the use of organotin antifouling paints on small boats in 1987, with similar measures being adopted in many countries. Despite some improvements, the continuing impacts on dogwhelks and other molluscs such as benthic clams Scrobicularia plana showed that the ban on leisure craft was only partly effective and that the commercial fleet (still entitled to use TBT) was a continuing threat to environmental quality particularly near ports (Langston et al, 1990; 2015) Langston and Burt 1991). These and similar observations, worldwide, led the International Maritime Organisation to implement a ‘global’ ban (2008), which effectively enforced removal, or sealing, of all tin-based coatings - which now appears to be achieving long-awaited improvement (Fig B). MBA long-term research on the behaviour, bioavailability and impacts of TBT remains highly relevant in terms of charting improvements in water quality.

The basic research into environmental behaviour, mechanisms and thresholds of toxicity, have contributed to the development of international regulatory measures (invoked to halt damage to vulnerable species and coastal ecosystems) and to the surveillance strategy to establish the success of these measures.

TBT-induced imposex in these marine snails remains the most specific and sensitive example of the threat of endocrine disrupting chemicals (EDC) on marine ecosystems and helped inform the development of TBT legislation that has had worldwide positive effects on environmental protection and ecosyste, rehabilitation. 

Figure;  A) Imposex in dogwhelk Nucella lapillus; trends in Vas Deference Sequence Index (VDSI) and B) trends in clam Scrobicularia plana populations (Warsash, Southampton) in the context of legislation on TBT in 1987 and 2008. (Note; despite some improvement, Falmouth dogwhelks still exhibit imposex due to the legacy of TBT in the environment (notably sediment))

Sources

Bryan, G.W., Gibbs, P.E., Hummerstone, L.G. et al. (1986). The decline of the gastropod Nucella lapillus around south west England: Evidence for the effect of tributyltin from antifouling paints. J Mar Biol Ass UK 66: 611-640.

Bryan, G.W., Gibbs, P.E., Burt, G.R. et al. (1987). The effects of tributyltin (TBT) accumulation on adult dog-whelks, Nucella lapillus: long-term field and laboratory experiments. J Mar Biol Ass UK 67: 525-544.

Langston, W. J. and Burt, G. R. (1991). Bioavailability and effects of sediment-bound TBT in deposit-feeding clams, Scrobicularia plana. Mar Environ Res, 32: 61-77.

Langston, W.J., Bryan, G.W., Burt, G.R. and Gibbs, P.E. (1990). Assessing the impact of tin and TBT in estuaries and coastal regions. Functional Ecology, 4, 433-443.