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 and have been banned by the International Convention on the Control of Harmful Anti-fouling Systems on Ships of the International Maritime Organization.
Uses include wood preservation, antifouling pesticide in marine paints, antifungal action in textiles and industrial water systems, such as cooling tower and refrigeration water systems, wood pulp and paper mill systems, and breweries. Tributyltin oxide is the most widely used compound in TBT–containing commercial products.
TBT compounds are considered toxic chemicals which have negative effects on humans and the environment. Tributyltin compounds are moderately to highly persistent organic pollutants that biomagnify up the marine predators' food net. One common example is leaching of TBT from marine paints into the aquatic environment, causing irreversible damage to the aquatic life. Tributyltin has also been linked to obesity in humans, as it triggers genes that cause the growth of fat cells.
TBT is harmful to some marine organisms, including the dog whelk. TBT causes dog whelks to suffer from imposex: females develop male sexual characteristics such as a penis. Trace amounts of just 2.4 nanograms of TBT per litre are needed to produce sexual changes in dog-whelks. This causes them to become infertile or even die. In severe cases males can develop egg sacs.
Tributyltin, dibutyltin and toxicity to marine mammals
Studies have shown that wild, dead sea otters (Enhydra lutris) and stranded bottlenose dolphins can have extremely high levels of tributyltin in their livers. Both tributyltin and dibutyltin, a metabolite byproduct, cause immunosuppression, leading to secondary infections. This was supported by the finding that otters dying of infectious causes tend to have higher levels of tissue butyltins than those dying of trauma or other causes.
Tributyltin toxicity to marine invertebrates
TBT is extremely toxic to molluscs. In the case of bivalve larvae, the effective concentration (EC50) of TBT is 1000 times lower than that of any other toxic compound introduced into the marine environment. TBT also causes imposex in marine gastropods and is probably responsible for reductions in their populations in zones with important ship traffic.
TBT compounds have been described to interfere with glucocorticoid metabolism, by inhibiting the activity of the enzyme 11beta-hydroxysteroiddehydrogenase type 2, which converts cortisol to cortisone.
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