Tributyltin

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Tributyltin (cation)
tributyltin hydride model

Tributyltin (TBT) compounds are a group of compounds containing the (C4H9)3Sn moiety, such as tributyltin hydride or tributyltin oxide. They are the main active ingredients in certain biocides used to control a broad spectrum of organisms. These compounds are included in the Rotterdam Convention[1] and have been banned by the International Convention on the Control of Harmful Anti-fouling Systems on Ships of the International Maritime Organization.[2]

TBT chemical properties[edit]

TBT compounds are organic derivatives of tin (Sn4+), where 3 carbon atoms covalently bonds the tin. The general formula for these compounds is (n-C4H9)3Sn-X. The X could be either an anion or a group linked covalently through an atom other than Carbon and Hydrogen. When introduced into an aquatic environment, TBT adheres to bed sediments because of its high specific gravity and low solubility. However, the adsorption of TBT to sediments is reversible, and can vary with the pH of the water. Therefore TBT can be released from the sediments, and back into the aquatic environment.[3]

Uses[edit]

TBT compounds were discovered in the 1950s in the Netherlands by a research group, van der Kerk, while trying to synthesize a powerful biocide for antifouling paint. It was found to be an incredibly effective biocide against aquatic species, but wrongly deemed safe enough to not cause damage to the marine environment. By the mid 60s it became the most popular antifouling paint worldwide. [4] TBT was mixed into paints to extend the life of antifouling coatings, and ships were able to continue operations for a longer time frame. The paints ensured fuel efficiency and delayed costly ship repairs. However, the TBT used on the ship hulls was found to leech into, and severely damage, the marine, brackish and freshwater environment. [5]

While its use has been banned worldwide, it is still being used illegally, especially in the Caribbean on cruise ships, because of its efficiency as an anti-fouling paint.

In the chemical laboratory, tributyltin hydride generated by the action of lithium aluminium hydride on tributyltin chloride is used to replace halogens in organic compounds for hydrogen.

Toxicity[edit]

After thirty years of research on the effects of TBT it has been concluded that TBT compounds leeching into the aquatic environment are incredibly toxic and have deleterious effects on the development and survival of the animals. The effects of antifouling paint go beyond the organisms that it is meant to kill. By killing off barnacles, algae, and other organisms at the bottom of the food chain the result is biomagnified up the marine predators' food net. It has been shown to have a harmful effects on many layers of the ecosystem, affecting invertebrates and vertebrates, including humans. Toxic effects in some species occur at 1 nano-gram per liter of water. [6] Even with its ban, TBT still presents a danger to the environment. One of the most problematic aspects of TBT is its accumulation in sediments and its long half life. TBT often bonds to suspended material and is carried down to the sediments, where it can remain, and be released, for up to 30 years. Additionally, TBT can be introduced into non-aquatic ecosystems because dissolved TBT can evaporate into the air and be dispersed by rain.[5]

Marine invertebrates[edit]

TBT has been shown to impact invertebrate development. Chironomus riparius has been used as a model invertebrate to test the effects of TBT on development and reproduction at sublethal concentrations found in marine environments. It was found that only 0.05 ng ml− 1 range is enough to have developmental effects on their larvae, and 10-100 ng l−1 was enough to seriously offset the female to male ratio in the population. At 10 ng l−1 females were at 55.6% of the population and 85.7% at 100 ng l− 1. These results contributed to data showing that male invertebrates are more sensitive to TBT, and that overall sensitivity may depend on gender. The results support claims that TBT has severely reduced populations of benthic invertebrates.[3]

Toxicity test performed on freshwater gastropod Lymnaea stagnalis revealed that 10 μg l− 1 could entirely inhibit egg development. At 1000 ng l− 1 there was low survival, with abnormal embryonic development leading to inhibition of shell growth. Also observed effects of TBT, are the deformation of shells in oysters and the masculinization of female marine sails (imposex).[5]

Marine mammals[edit]

Oryzias latipes, medaka, has been used as a model vertebrate organism to test for effects of TBT at developmental stages of the embryo. It was observed that developmental rate was slowed by TBT in a concentration-related manner and that tail abnormalities occurred.

While invertebrates and fish mainly uptake the organic contaminants from the surroundings, the main way that higher mammals like birds and mammals are exposed to TBT is through the diet. The liver is most heavily effected by presence of TBT. Studies have shown that Tributyltin links to obesity, by activating retinoid X receptors (RXRS) which enter the nuclei of cells and switch on genes that cause the growth of fat storage cells. TBT compounds have been described to interfere with glucocorticoid metabolism in the liver, by inhibiting the activity of the enzyme 11beta-hydroxysteroiddehydrogenase type 2, which converts cortisol to cortisone.[5]

TBT has also been shown to lead to immunosuppression in mammals such as sea-otters and dolphins. Studies have shown that wild, dead sea otters (Enhydra lutris) and stranded bottlenose dolphins can have extremely high levels of tributyltin in their livers.[7] In addition, it was found that otters dying of infectious causes tend to have higher levels of tissue butyltins than those dying of trauma or other causes.[8]

TBT has also been blamed by hearing experts for causing hearing loss in mammalian top predators such as toothed whales.[9][10]

Past and current responses[edit]

The use organotin compounds acting as biocide in anti-fouling systems has been completely banned in 2008 by the International Convention on the Control of Harmful Anti-fouling Systems on Ships of the International Maritime Organization.[2]

Because TBT is the most effective antifouling agent discovered, it is frequently used in antifouling paint throughout the globe. It's inexpensive cost has been a major factor when resisting complete prohibition. The Environmental Protection Agency (EPA) recognized that using TBT-based antifouling agents over the standard copper formula could save the United States Navy 130 million dollars a year.

Bans on TBT on boats less than 25 metres long first started in the 1980's by various countries. In 1990, the Marine Environment Protection Committee adopted Resolution MEPC 46(30), which recommended that the Government eliminate the use of TBT-containing antifouling paints on smaller vessels. This resolution was intended to be a temporary restriction until the International Maritime Organization could implement a complete ban of TBT antifouling agents for ships. Several countries followed with a ban of use, and in 1997 Japan banned the production of TBT-based anti-fouling paints. [2]

See also[edit]

References[edit]

  1. ^ Secretariat for the Rotterdam Convention on the Prior Informed Consent Procedure for Certain Hazardous Chemicals and Pesticides in International Trade (1 February 2009). "Decision Guidance Document for Tributyltin Compounds". United Nations Environment Programme. Retrieved 2013-01-04. 
  2. ^ a b c "Focus on IMO - Anti-fouling systems". International Maritime Organisation. 
  3. ^ a b Antizar-Ladislao, Blanca (Feb. 2008). "Environmental levels, toxicity and human exposure to tributyltin (TBT)-contaminated marine environment. A review". Environmental International 34 (2): 292–308. PMID 17959247. Retrieved 3/12/14. 
  4. ^ Konstantinou, Ioannis (Feb 22, 2006). Antifouling Paint Biocides. Springer. p. 1. 
  5. ^ a b c d Mora, ed. by Stephen J. De (1996). Tributyltin : case study of an environmental contaminant (1. publ. ed.). Cambridge [u.a.]: Cambridge Univ. Press. ISBN 0521470463. 
  6. ^ Walmsley, Simon. "Tributyltin pollution on a global scale. An overview of relevant and recent research: impacts and issues.". WWF UK. 
  7. ^ Murata S, Takahashi S, Agusa T, Thomas NJ, Kannan K, Tanabe S (April 2008). "Contamination status and accumulation profiles of organotins in sea otters (Enhydra lutris) found dead along the coasts of California, Washington, Alaska (USA), and Kamchatka (Russia)". Marine pollution bulletin 56 (4): 641–9. doi:10.1016/j.marpolbul.2008.01.019. PMID 18304586. 
  8. ^ Kannan et al. 1998. Butyltin residues in Southern sea otters (Enhydra lutris nereis) found dead along California coastal waters. Environ. Sci. Technol. 32:1169-1175
  9. ^ Matt Apuzzo (2005-01-28). "Whale Deafness Linked To Chemical". Associated Press via CBS News. Retrieved 2008-07-30. 
  10. ^ Santos-Sacchi Joseph, Song Lei, Zheng Jiefu, Nuttall Alfred L (2006-04-12). "Control of Mammalian Cochlear Amplification by Chloride Anions". Journal of Neuroscience 26 (15): 3992–3998. doi:10.1523/JNEUROSCI.4548-05.2006. PMID 16611815. 

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