Tributyltin (TBT) Flashcards
What is Biofouling?
Settlement and accumulation of living organisms on man-made physical structures placed in an aquatic or marine environment
What fouling organisms are there?
bacterial slime diatoms algae sponges tubeworms bryozoa mussels barnacles
Why is biofouling economically important?
- increases frictional resistance (drag) in fouled ships
- structural deterioration (corrosion) of engineered materials
- restricted flow through fouled aquaculture cage netting
- mechanical blockage of intake and outfall pipes
- losses in heat transfer efficiency of marine cooling systems
- increased costs for maintaining/replacing all of the above
What effects does biofouling have on speed and fuel consumption?
- Can reduce vessel speed by up to 10%
- 10 micrometer increase in average hull roughness can result in 0.3 to 1% increase in fuel consumption
- up to 40% increase in fuel consumption needed to counter drag
- large vessels fuel costs can be as much as 50 percent of operating costs
- US navy spends ~1 billion dollars on extra fuel and maintenance to counter effects of biofouling
Why are antifoulants beneficial?
Saves shipping industry 7.2 millions tonnes of fuel per annum
Estimates saving of 22 million tonnes of CO2
How do antifouling paints work?
- Work by releasing small amounts of biocides at paint surface, killing settling stages of fouling organisms
Points about TBT
- introduced in the 1960s and proved very effective
- degrades through debutylisation (triBT, diBT, monoBT)
- biodegradable
- action of bacteria and phytoplankton aids the breakdown
- higher temperature and nitrate supplementation promote breakdown
- adsoprtion on particles leads to incorporation into sediments
- half life ~2 years reported for anaerobic sediments
Stats regarding TBT in Rotterdam harbour
- 20 million tonnes of sludge dredged annually
- TBT in sediments 500 times acceptable levels
- 16 million tonnes dumped at sea
- 4 million tonnes considered “heavily contaminated”
What is the danger of TBT?
- caused a decline in oysters and whelks in 1960s in UK and France
- Investigations in Plymouth in 1960s showed high degree of imposex (masuclinisation) in dog whelps
Dog Whelk stats
Dog whelk (Nucella lapillus)
- widely distributed on rocky shores from Straits of Gibraltar to Arctic
- Gonochoristic (one of 2 distinct sexes)
- lays vase shaped egg capsules attached to rocky substrate
- direct development (no planktonic stage)
How many species of gastropod have been found to be affected with imposex?
72 spp. (Schulte-Oehlmann et al., 1997)
What is the toxicity of TBT to other organisms?
- Molluscs - most sensitive (<10ng/l)
- Copepods, echinoderms, polychaetes, tunicates 10-100ng/l range
- Fish (adult), decapod crustacea relatively resistant
How can otters and bottlenose dolphins be linked to TBT?
bioaccumulation - dead otters and stranded dolphins can have extremely high levels of TBT in their livers
TBT is known to cause immunosurpression leaving them vulnerable to infections
What and when were the regulations imposed on TBT?
- French reugulate use of TBT (1983)
- British ban use on boats under 25m (1985)
- US congress pass regulations (1988)
- IMO resolution (1990)
- draft proposal to phase out TBT by 2006 (1996)
- TBT banned on ships (2007)
- EC782/2003 bans applications on EU flagged vessels and as of 2008 becomes an offence for any ship visiting an EU port to have TBT present on its hull
What happened after the bans?
- TBT breaks down in 1-3 months in aerobic conditions
- bivalve recruitment dramatically improved
- imposex reduced, but still observed 7 years after French ban
- Deposit feeding bivalves showed no recovery 2 years after ban
