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Tributyltin (TBT) is an
umbrella term
In linguistics, semantics, general semantics, and ontologies, hyponymy () is a semantic relation between a hyponym denoting a subtype and a hypernym or hyperonym (sometimes called umbrella term or blanket term) denoting a supertype. In other wor ...
for a class of
organotin
Organotin compounds or stannanes are chemical compounds based on tin with hydrocarbon substituents. Organotin chemistry is part of the wider field of organometallic chemistry. The first organotin compound was diethyltin diiodide (), discovered by ...
compounds which contain the
(C4H9)3 Sn group
A group is a number of persons or things that are located, gathered, or classed together.
Groups of people
* Cultural group, a group whose members share the same cultural identity
* Ethnic group, a group whose members share the same ethnic ide ...
, with a prominent example being
tributyltin oxide
Tributyltin oxide (TBTO) is an organotin compound chiefly used as a biocide (fungicide and molluscicide), especially a wood preservative. Its chemical formula is C4H9)3Snsub>2O. It is a colorless viscous liquid. It is poorly soluble in water (20 ...
.
For 40 years TBT was used as a
biocide
A biocide is defined in the European legislation as a chemical substance or microorganism intended to destroy, deter, render harmless, or exert a controlling effect on any harmful organism. The US Environmental Protection Agency (EPA) uses a slig ...
in
anti-fouling paint
Anti-fouling paint is a specialized category of coatings applied as the outer (outboard) layer to the hull of a ship or boat, to slow the growth of and facilitate detachment of subaquatic organisms that attach to the hull and can affect a vess ...
, commonly known as
bottom paint
Bottom may refer to:
Anatomy and sex
* Bottom (BDSM), the partner in a BDSM who takes the passive, receiving, or obedient role, to that of the top or dominant
* Bottom (sex), a term used by gay couples and BDSM
* Buttocks or bottom, part of t ...
, applied to the hulls of oceangoing vessels. Bottom paint improves ship performance and durability as it reduces the rate of
biofouling
Biofouling or biological fouling is the accumulation of microorganisms, plants, algae, or small animals where it is not wanted on surfaces such as ship and submarine hulls, devices such as water inlets, pipework, grates, ponds, and rivers that ...
, the growth of organisms on the ship's hull. The TBT slowly leaches out into the marine environment where it is highly toxic toward nontarget organisms. TBT toxicity can lead to biomagnification or bioaccumulation within such nontarget organisms like invertebrates, vertebrates, and a variety of mammals. TBT is also an
obesogen
Obesogens are foreign chemical compounds that are hypothesised to disrupt normal development and balance of lipid metabolism, which in some cases, can lead to obesity. Obesogens may be functionally defined as chemicals that inappropriately alter ...
. After it led to collapse of local populations of organisms, TBT was banned.
Chemical properties
TBT, or tributyltin, tributylstannyl or tributyl stannic hydride compounds are
organotin compound
Organotin compounds or stannanes are chemical compounds based on tin with hydrocarbon substituents. Organotin chemistry is part of the wider field of organometallic chemistry. The first organotin compound was diethyltin diiodide (), discovered by ...
s. They have three butyl groups covalently bonded to a tin(IV) centre.
[Davies, Alwyn George. (2004) Organotin Chemistry, 2nd Edition Weinheim: Wiley-VCH. ] A general formula for these compounds is (''n''-C
4H
9)
3Sn-X. The “X”, typically occurs in three forms, each an electronegative compound bound to a chloride, hydroxide, or a
carboxylate
In organic chemistry, a carboxylate is the conjugate base of a carboxylic acid, (or ). It is an ion with negative charge.
Carboxylate salts are salts that have the general formula , where M is a metal and ''n'' is 1, 2,...; ''carboxylat ...
.
TBT is also known to be an endocrine disrupting compound, which influences biological activities such as growth, reproduction and other physiological processes.
TBT compounds have a low water solubility, a property that is ideal for antifouling agents. The toxicity of TBT prevents the growth of algae, barnacles, molluscs and other organisms on ships hulls.
When introduced into a marine or aquatic environment, TBT adheres to bed sediments. TBT has a low Log K
ow of 3.19 – 3.84 in distilled water and 3.54 for sea water, this makes TBT moderately hydrophobic. TBT compounds have a high fat solubility and tend to absorb more readily to organic matter in soils or sediment. The bioaccumulation of TBT in organisms such as molluscs, oysters and dolphins, have extreme effects on their reproductive systems, central nervous systems and endocrine systems. However, the adsorption of TBT to sediments is reversible and depends on pH level in the body of water.
TBT has a half-life of one or two weeks in marine water.
When it accumulates in sediments its half life is about 2 years. TBT often bonds to suspended material and sediments, where it can remain and be released for up to 30 years.
Studies have shown that 95% of TBT can be released from the sediments back into the aquatic environment. This absorption process can complicate quantification of TBT in an environment, since its concentration in the water is not representative of its availability.
Uses
Tributyltin (TBT) compounds are
biocide
A biocide is defined in the European legislation as a chemical substance or microorganism intended to destroy, deter, render harmless, or exert a controlling effect on any harmful organism. The US Environmental Protection Agency (EPA) uses a slig ...
s. TBT's antifouling properties were discovered in the 1950s in the Netherlands by van der Kerk and coworkers. It prevents microorganisms from settling on the hull of a ship and poisons the organisms that end up settling. By the mid 1960s, it had become the most popular
anti-fouling paint
Anti-fouling paint is a specialized category of coatings applied as the outer (outboard) layer to the hull of a ship or boat, to slow the growth of and facilitate detachment of subaquatic organisms that attach to the hull and can affect a vess ...
around the globe.
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. It is also relatively inexpensive.
TBT is also an ingredient in some
disinfectant
A disinfectant is a chemical substance or compound used to inactivate or destroy microorganisms on inert surfaces. Disinfection does not necessarily kill all microorganisms, especially resistant bacterial spores; it is less effective than st ...
s, for example in combination with
quaternary ammonium
In chemistry, quaternary ammonium cations, also known as quats, are positively charged polyatomic ions of the structure , R being an alkyl group or an aryl group. Unlike the ammonium ion () and the primary, secondary, or tertiary ammonium cations ...
compounds. Additionally, TBT has been used in the fertilizer, textile, and wood industries. It has antifungal properties that make it useful for both the production of textiles and wood preservation, and in the creation of biocides for paired use with fertilizers. Another use of TBT is that they were used as stabilizers in compounds like polyvinyl chlorides.
Due to this usage of TBT, there are a variety of consumer products where traces of TBT can be found, like in textile fabrics, plastic polymers, silicon, and many more.
Toxicity
The effects of antifouling paint go beyond the organisms that it is intended to kill. By poisoning barnacles, algae, and other organisms at the bottom of the food chain, the bioaccumulation of TBT increases over time affecting more and more of the bottom feeders of the aquatic food web environment, which are mainly invertebrates and are affected by TBT. There is a slight biomagnification of TPT that has been demonstrated in the lower part of the marine food chain (i.e., planktonic organisms, invertebrates, and fishes). However, the biomagnification of TBT into larger marine animals such as marine mammals is debatable. Toxic effects in some species occur at 1 nano-gram per liter of water. Air pollution from TBT has not been noticed or considered significant enough to effect the environment. In the water, photodegradation and microorganisms can break down TBT and leach into the soil sediments.
Bioaccumulation and biomagnification
As TBT is most often used as a biofouling agent, it bioaccumulates in marine wildlife such as molluscs, with levels being higher in organisms and sediments in and around areas of high maritime activity, such as ports and harbours.
The bioaccumulation increases over time, leading to a biomagnification in organisms higher up the food chain, although the biomagnification is not that considerable in size. As TBT can remain in the environment for up to 30 years due to often bonding to suspended material and sediments, it can remain in an ecosystem for a very long time. This means that bioaccumulation readily occurs in marine environments, which can lead to very high amounts of TBT being accumulated, especially in smaller organisms at the bottom of the food chain, which in turn has various health effects.
Invertebrates
Exposure to organotin compounds causes the development of male accessory sex organs in female prosobranch gastropods. This phenomenon has been termed imposex. TBT has been shown to affect
invertebrate
Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...
development. Marine snails, such as the
dog whelk
The dog whelk, dogwhelk, or Atlantic dogwinkle (''Nucella lapillus'') is a species of predatory sea snail, a carnivorous marine gastropod in the family Muricidae, the rock snails.
''Nucella lapillus'' was originally described by Carl Linnaeus i ...
(''Nucella lapillus''), has often been used as an
indicator species
A bioindicator is any species (an indicator species) or group of species whose function, population, or status can reveal the qualitative status of the environment. The most common indicator species are animals. For example, copepods and other sma ...
. In gastropods, the normal process of accessory sex organ development is retinoid dependent, as has been proven by the effect 9cisRA has on male penises. TBTs mimic the endogenous ligand of Retinoid X Receptor (9cisRA), and thus activates the signalling cascades that are retinoid acid dependent, promoting female penis growth.
There have been many theories as to why molluscs are affected by TBT. For example, previous literature has stated that TBT would cause the inhibition of aromatase which would lead to an increase in testosterone and therefore, causing imposex. It was theorized that TBT disrupts endocrine system by inhibiting cytochrome P450 molecule. Among its myriad functions, P450 converts androgen, which has male-hormone properties, into oestrogen, which has female hormone properties. It was theorized that the high concentration of androgen lead to the masculinization of females. Another indicator species is ''
Chironomus riparius
''Chironomus riparius'', also known as ''Chironomus thummi'' and commonly known as the harlequin fly, is a species of non-biting midge. Their larvae are known by the common name of blood worm due to their red colouration. It is common in both Nor ...
'', a species of non-biting
midge
A midge is any small fly, including species in several families of non-mosquito Nematoceran Diptera. Midges are found (seasonally or otherwise) on practically every land area outside permanently arid deserts and the frigid zones. Some mid ...
, which has been used to test the effects of TBT on development and reproduction at sublethal concentrations found in marine environments. Higher concentrations of TBT were found to increase the female population and the results are interesting because unlike the
masculinization
Virilization or masculinization is the biological development of adult male characteristics in young males or females. Most of the changes of virilization are produced by androgens.
Virilization is most commonly used in three medical and biology ...
of the stengoglassan gastropods, feminization was present.
Vertebrates
Vertebrates become affected by the waters contaminated with TBT, as well as by consuming organisms that have already been poisoned. ''Oryzias latipes'', commonly called
Japanese rice fish
The Japanese rice fish (''Oryzias latipes''), also known as the medaka, is a member of genus ''Oryzias'' ( ricefish), the only genus in the subfamily Oryziinae. This small (up to about ) native of East Asia is a denizen of rice paddies, marshes, ...
, 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. Illustrating the infiltration of TBT in the food chain, one study showed that most samples of
skipjack tuna tested positive for presence of TBT. Tuna from waters around developing Asian nations had particularly high levels of TBT. Regulation of TBT is not enforced in Asia as rigorously as in Europe or US. Studies have shown that TBT is detrimental to the immune system. Research shows that TBT reduces resistance to infection in fish which live on the seabed and are exposed to high levels of TBT. These areas tend to have silty sediment like harbours and estuaries.
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.
Mammals
TBT can enter the diet of humans and other mammals such as whales, dolphins, dugongs, and sea otters. As of 2008 high levels of tributyltin have been detected in the livers of
sea otter
The sea otter (''Enhydra lutris'') is a marine mammal native to the coasts of the northern and eastern North Pacific Ocean. Adult sea otters typically weigh between , making them the heaviest members of the weasel family, but among the small ...
s (''Enhydra lutris'') and stranded
bottlenose dolphin
Bottlenose dolphins are aquatic mammals in the genus ''Tursiops.'' They are common, cosmopolitan members of the family Delphinidae, the family of oceanic dolphins. Molecular studies show the genus definitively contains two species: the common ...
s.
Otters dying of infectious causes tended to have higher levels of tissue butyltins than those dying of trauma or other causes. It was also reported by scientists that sea otters typically stay near boats and closed off marinas, which may have led to these organisms experiencing higher levels of butyltins. TBT has been shown to lead to immunosuppression in sea-otters and dolphins. TBT has also been linked to hearing loss in mammalian top predators such as
toothed whale
The toothed whales (also called odontocetes, systematic name Odontoceti) are a parvorder of cetaceans that includes dolphins, porpoises, and all other whales possessing teeth, such as the beaked whales and sperm whales. Seventy-three species of ...
s. In rats, the hypothalamus-pituitary-adrenal (HPA) axis can be affected by TBT. In the pituitary and adrenal glands, there have been findings of morphophysiological changes within rats affected by TBT. TBT can also affect humans as well. Humans can be exposed to these compounds and potentially experience headaches, fatigue, respiratory issues, and more. Long-term exposure can also lead to damage of some internal organs such as the kidneys and liver.
Regulation
Bans on TBT on boats less than 25 metres long first started in the 1980s. 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
The International Maritime Organization (IMO, French: ''Organisation maritime internationale'') is a specialised agency of the United Nations responsible for regulating shipping. The IMO was established following agreement at a UN conference ...
could implement a ban of TBT anti-fouling agents for ships. Several countries followed and in 1997, Japan banned the production of TBT-based anti-fouling paints. The IMO began to use an Assembly resolution in 1999 that essentially wanted the MPEC to fix the severe environmental effects of the anti-fouling systems. This led to a worldwide ban on organotin compound applications on ships starting in 2003.
In 2008,
organotin compounds
Organotin compounds or stannanes are chemical compounds based on tin with hydrocarbon substituents. Organotin chemistry is part of the wider field of organometallic chemistry. The first organotin compound was diethyltin diiodide (), discovered by ...
acting as biocide like TBT compounds were banned entirely in anti-fouling paint and included in the
Rotterdam Convention
The Rotterdam Convention (formally, the Rotterdam Convention on the Prior Informed Consent Procedure for Certain Hazardous Chemicals and Pesticides in International Trade) is a multilateral treaty to promote shared responsibilities in relation ...
and have been banned by the
of the International Maritime Organization.
It states that ships cannot bear
organotin compounds
Organotin compounds or stannanes are chemical compounds based on tin with hydrocarbon substituents. Organotin chemistry is part of the wider field of organometallic chemistry. The first organotin compound was diethyltin diiodide (), discovered by ...
on their hulls or external parts or surfaces, unless there is a coating that forms a barrier so that organotin compounds cannot leach out to reduce exposure by allowing recovery to occur.
Violations of the ban on TBT
Although the ban on TBT use was proved to be effective on reducing the negative effects on the environment, some people that supplied them were still producing and selling them to other countries for a profit. Even though banned by some international agencies like the International Maritime Organization, TBT anti-fouling paints are still used in countries with poor regulation enforcement to this day, with the Caribbean being a prime example.
U.S. Violations
In November 2018, the US Department of Justice announced that three people they had charged and arrested in New Jersey for manufacturing and selling tributyltin based marine paint had pleaded guilty. The sentencing of these people was scheduled for February 2019.
See also
*
Triphenyltin
*
Organotin chemistry
Organotin compounds or stannanes are chemical compounds based on tin with hydrocarbon substituents. Organotin chemistry is part of the wider field of organometallic chemistry. The first organotin compound was diethyltin diiodide (), discovered b ...
*
Biomimetic antifouling coating
A biomimetic antifouling coating is a treatment that prevents the accumulation of marine organisms on a surface. Typical antifouling coatings are not biomimetic but are based on synthetic chemical compounds that can have deleterious effects on the ...
References
{{reflist
External links
Newcastle University Biofouling Group"Ambient Aquatic Life Water Quality Criteria for Tributyltin (TBT)"United States Environmental Protection Agency
The Environmental Protection Agency (EPA) is an independent executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it be ...
, December 2003
Pesticides
Endocrine disruptors
Organotin compounds