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Tributyltin compounds

TBTs

SPRI Emission Reporting Threshold
0.005 Kg/yr Pollutant Emissions to Water
0.005 Kg/yr Pollutant Emissions to Waste Water
1.00 Kg/yr Pollutant Emissions to Land
Disclaimer
This sheet is a generic summary, designed to give the reader a basic level of background information about the substance in question. Great care has been taken to represent as effectively and correctly as possible the broad range of (not necessarily consistent) information which is available from a variety of sources. The reader must accept therefore that this sheet has no legal status and cannot be relied upon in any legal proceedings. SEPA disclaims any responsibility or liability whatsoever for errors and omissions in this sheet.
What is it?
Under normal conditions, Tributyltin Compounds (TBTs) are usually found as thin colourless or pale yellow liquids, which have a weak, but sometimes unpleasant, smell. Most TBT compounds are stable under normal conditions. TBTs boils at between 150 and 200 degrees celsius. TBTs are only slightly soluble in water, but will dissolve well in most organic (carbon-containing) solvents.
What is it used for?
The most common use of TBTs is as marine anti-fouling agents, to prevent the growth of algae and barnacles on the hull of ships, on quayside constructions and on fishing nets and shellfish pots. They are also used more generally as fungicides in preservatives for wood, textiles, paper, leather, plastics and packaging and in food additives. Some TBTs are added to plastics and other materials because of their stabilising and anti-corrosive properties.
Where does it come from?
The most significant releases of TBTs are likely to occur as gradual leaching from products treated with pesticides containing them. They might also be released from industry during their manufacture and the production of products to which they are added, their transport and storage. There are not thought to be any natural sources of TBTs to the environment.
How might it affect the environment?
TBTs are toxic to fish and other aquatic life and are accumulated by these species. TBTs can bind strongly to particles in water bodies and to sediments and can then persist for a considerable time. Their low solubility in water however means that they are not particularly mobile. Land animals might be exposed to TBTs when it has been used to treat wood for example. High levels may cause harm. There is concern that exposure to TBTs can interfere with animal hormones, that they are "endocrine disruptors". It is not considered likely that TBT pollution has any effects on the global environment.
How might exposure to it affect human health?
Expousure to tributyltin compounds mainly occurs in the occupational setting. Tributyltin compounds can enter the body either by inhalation of air containing tributyltin compounds, ingestion of contaminated food or water, or by dermal contact with tributyltin. Inhalation of air containing tributyltin compounds can cause irritation of the upper respiratory tract, chest tightness, breathing difficulties, dizziness, headache, tremors, lack of coordination and flu-like symptoms. There is no evidence for the effects of ingestion of tributyltin compounds on human health. Dermal contact with tributyltin compounds can cause sever skin irritation, chemical burns and dermatitis. Contact with the eyes can cause irritation. The International Agency for Research on Cancer has not designated tributyltin compounds in terms of their carcinogenicity. However, exposure to tributyltin compounds at normal background levels is unlikely to have any adverse effect on human health.
What steps are being taken to limit the potential impacts?
TBTs are UK "Red List" pollutants, signifying that their presence in the environment is of particular concern. Releases of TBTs are controlled through the UK Pollution, Prevention and Control (PPC) Regulations, the Food and Environmental Protection Act (FEPA 1985), the Control of Pesticides Regulations (COPR 1986) and the UK Surface Waters Regulations (SI 1997/2560). European Directives regulating levels of TBTs include that concerned with pollution of the aquatic environment (76/464/EEC) and they are listed as a priority substances for the Water Framework Directive. At an international level, the use of TBTs in marine situations is gradually being phased out as the potentially harmful effects they may have on aquatic life are recognised. In the UK, for example, the use of TBTs is restricted to large boats (of more than 25 metres in length). TBTs are also listed as substances for priority action under the Helsinki and OSPAR Conventions which protect the marine environments of the Baltic Sea and north-east Atlantic Ocean respectively.