A Pesticide Information Project of Cooperative Extension Offices of Cornell University, Michigan State University, Oregon State University, and University of California at Davis. Major support and funding was provided by the USDA/Extension Service/National Agricultural Pesticide Impact Assessment Program.
TBT by itself is unstable and will break down in the environment unless it is combined with an element such as oxygen. One of the most common TBT compounds is bis(tributyltin) oxide, or TBTO. This form has been the subject of most TBT testing.
TBTO and eight additional TBT compounds are registered for use as marine antifoulants. Other TBT compounds are used as disinfectants, fungicidal wood preservatives, textile disinfectants, and stabilizers in PVC resin. Paper and pulp mills, cooling towers, breweries, textile mills and leather-processing facilities may also use some forms of TBT. Collectively these compounds are refered to as organotins.
All of the organotins are now regulated by the "Organotin Antifouling Paint Control Act of 1988." This act regulates the use of these materials in paints and sets standards for the amount of biocides that can leach from the paint into water.
TBT compounds damage the immune system. One study of male rats fed TBTO daily for six weeks resulted in decreased resistance to infection (10).
TBT is extremely toxic to crustaceans. Lobster larvae show a nearly complete decrease in growth at just 1.0 ppb TBT (1). Molluscs, used as indicators of TBT pollution because of their high sensitivity to these chemicals, react adversely to very low levels of TBT (0.06-2.3 ppb). They release TBT very slowly from their bodies after it has been absorbed.
TBT toxicity in the field may be substantially underestimated in laboratory studies (1). TBT binds to the sides of containers and plankton which contributes to this underestimation of it's potential toxicity. Generally, the larvae of any tested species are more sensitive to tributyltin exposure than are the adults.
The present use of TBT in antifouling paints may cause TBT exposure to nontarget aquatic organisms such as mussels, clams, and oysters. At low levels, TBT can cause structural changes and growth retardation (3).
Imposex, the development of male characteristics in females, has been initiated by TBT exposure in several snail species. In laboratory tests, reproduction was inhibited when female snails exposed to 50 ppt of TBT developed male characteristics (1). Imposex was also noted in the mud snail, or dogwhelk, at less than 3 ppt TBT (1).
Oysters in France and England's marine waters are adversely affected by TBT exposure. TBT-exposed oysters have abnormal shell development, poor weight gain, brittle shells and imposex.
Some fin fish can degrade TBT because of special enzymes these fish contain. Once absorbed in Chinook salmon, TBT breaks down into di-n-butyltin (DBT). Rainbow trout eggs are killed within 10-12 days when exposed to 5 ppb TBT. At lower levels, no deaths occurred, but blood and liver metabolism changes were noticed (6). Growth reduction and liver changes also occurred in young trout exposed to low levels of tributyltin chloride. Also, after seven days at low levels of TBTO, the corneal membranes of the rainbow trouts' eyes were destroyed (1).
TBTO has been shown to inhibit cell survival of marine unicellular algae at very low concentrations; the 72-hour EC50 ranges from 0.33 ppb to 1.03 ppb (1).
TBT is highly attracted to fats and tends to be stored in these tissues. TBT is accumulated in oysters, mussels, crustaceans, molluscs, fish, and algae. Freshwater species will bio-accumulate more TBT than will marine organisms.
Oysters bioaccummulate TBT compounds readily, reach an equilibrium uptake soon after exposure, and are slow to release this chemical. Oysters exposed to very low TBTO concentrations bioaccumulated TBT 1,000 to 6,000 fold. Specific bioaccumulation factors vary depending on the species.
Evidence of organotins entering the human diet has been observed with Chinook salmon, which may be commercially raised in TBT-treated pens. Juvenile chinook salmon accumulate TBT immediately upon exposure to low TBT concentrations. TBT and its metabolite, DBT, were found in the salmon's muscle tissue (8).
Under aerobic conditions, tributyltin takes one to three months to degrade. But in anaerobic (airless) soils, this compound will persist for more than two years.
Because of the low water solubility (inability to dissolve in water) of TBT and other properties, it will bind strongly to suspended material such as minute organic material or inorganic sediments (4). The extent of binding to bottom sediment will vary with location, organic content, particle size, and type of material.
The half-life of TBT in water is about three months. Also, the chemical nature of TBT compounds generally keeps them within the water areas where they were applied.
Levels up to 800 ppt have been found along the East Coast of the United States. In the Great Lakes, concentrations from 20 to 840 ppt have been recorded. San Diego Bay has reached 1,000 ppt TBT (11).
It has not been found in groundwater.
Two kinds of TBT-containing paints are known. Free-association paint, made by mixing TBT into the paint, dissolves when it contacts water. All of the TBT is leached out from the paint in 12-24 months. In copolymer paint, the TBT is bound to the paint and slowly releases with water movement, and is effective for five to six years.
The EPA has established a cut-off release rate of 4.0 ug/cm2/day as sufficient to keep a ship's hull free of fouling, while causing minimal risk to aquatic mammals.
|TOL:||5 ppm (5)|
|TLV:||10 ppm (TWA); 20 ppm (STEL) (5)|
|Drinking water health advisory:||2 ppt (British)|
|Criterion Maximum Concentration (acute):||150 ppt (freshwater), 240 ppt (saltwater)|
|Criterion Continuous Concentration (chronic):||20 ppt (freshwater), 30 ppt (saltwater)|
|Solubility in water:||considered insoluble; about 1 ppm (4).|
|Solubility insolvents:||soluble in hexane and most organic solvents|
|Melting point:||53 degrees C (5)|
|Boiling point:||193 degrees C (5)|
|Vapor pressure:||1 mm Hg at 20 degrees C (5)|
|Kow:||5500 in 32% seawater (4)|
|BCF:||about 260 (4), varies with species.|
Pesticide and Toxic Chemical News. October 7, 1987. pp. 17-18. Huggett, Robert J, M.A. Unger, P.F. Seligman and A.O. Valkirs. 1992. The Marine Biocide Tributyltin. Environmental Science and Technology. Vol 26(2) Cooper, W. May 15, 1987. Environmental Impact Statements (EIS) Status Report. Michigan Environmental Review Board/Interdepartmental Environmental Review Committee. MERB, Department of Commerce, Lansing, MI. Goldberg, E.D. October, 1986. "TBT. An Environmental Dilemma." Environment. 28:17-21, 42. Hugget, R.J. September 30, 1986. "Tributyltin Based Antifouling Paints -- Environmental Issues." Testimony before the Subcommittee on Oversight and Investigations of the House of Representatives Committee on Merchant Marine and Fisheries. Pesticide and Toxic Chemical News. May 6, 1987. pp. 4-7. Wood, E. March 1986. "Organotin Anti-Fouling Paints, An Environmental Problem?" Marine Conservation Society. Herefordshire. The Bureau of National Affairs, Inc. TBT Paints may be restricted in spring 1987. Chem. Reg. Reporter. 3 October 1986, pp. 814-815.