NOSB paper

This paper was written as part of the 2004 Alaska Ocean Sciences Bowl high school competition. The conclusions in this report are solely those of the student authors.

The Effects of Tributyltin on the Marine Environment


Heather Roach
Brandy King
Kelly King
Sheila Oelrich


Team Tributyltin
Soldotna High School
425 West Marydale
Soldotna, AK 99669

Soldotna Team Tributyltin photo


Pollutants that resist breakdown and accumulate in the food chain are of great concern because they are consumed or absorbed by fish and other marine wildlife, which in turn are consumed by humans (NOAA, 2003). One of the most dangerous and controversial contaminants today is tributyltin (TBT). Tributyltin is one of the most poisonous substances to be released to the aquatic environment (Knutzen, 1995). It is used in many of the world's marine paints to keep barnacles, seaweed, and other organisms from clinging to ships. In mammals, high levels of TBT can be damaging to the endocrine glands, as well as the reproductive and central nervous systems, bone structure, and the gastrointestinal tract of mammals (McGinn, 2000).

Tributyltin is also harmful to crustaceans. It has been shown that TBT contamination causes shell thickening and deformation in adult oysters (crassostrea gigas) and reduces larval success. TBT causes imposex in many crustaceans; which is the formation of male sexual characteristics on female organisms (Botfield, 2000).

There have been several laws passed by the International Maritime Organization preventing the use of TBT based paints on smaller boats, and more recently, on all vessels. However, many people are not aware of these laws, especially in more remote areas like Homer. There are several alternative products on the market, which we will later explore. Continuing to use TBT based products will only continue to harm the environment, and an alternative paint is the best solution for this worldwide problem.

Pollution and Contamination

Pollution is on the rise and is a major factor in the world today. Pollution does not only occur on land, it also is a major issue in our oceans, lakes and rivers. Oil pollution, debris, mining and dumping, raw sewage and increased fishing are very real ways that we are damaging our oceans, which make up about two thirds of our earth (Cornish, 1998). For thousands of years, humans have viewed oceans as vast dumps for domestic, municipal, and industrial garbage–tons of sediments dredged from harbors and waterways, sewage sludge, toxic industrial by-products, even low-level radioactive waste. These materials may never become evenly diluted into a weakened mixture, and ocean processes may even concentrate some materials (Cornish, 1998).

Pollutants that resist breakdown and accumulate in the food chain are of greatest concern because they are consumed or absorbed by fish and wildlife, which in turn are consumed by humans (NOAA, 2003). The chemical contamination of sediments continues to affect large coastal areas, threaten human health and reduce the economic well being of regions that depend on a healthy coastal environment (NOAA, 2003).

Human activities on land cause a large portion of offshore contamination. An estimated 44% of marine pollution comes from land-based pathways, flowing down rivers into tidal estuaries, where it bleeds out to sea; an additional 33% is airborne pollution that is carried by winds and deposited far off shore (McGinn, 2000).

Our oceans are too important to continue this behavior. Oceans are a source of food and fuel, a means of trade and commerce, and a base for cities and tourism (McGinn, 2000). Harboring a greater variety of animal body types (phyla) than terrestrial systems and supplying more than half of the planet's ecological goods and services, the oceans play a commanding role in the Earth's balance of life (McGinn, 2000). The share of overexploited marine fish species jumped from almost none in 1950 to 35% in 1996, with an additional 25% nearing full exploitation. More than half of the world's coastlines and 60% of the coral reefs are threatened by human activities, including intensive coastal development, pollution, and over fishing (McGinn, 2000).

Human's pollution is especially threatening in our own neighborhood. Homer, Alaska is the halibut fishing capital of the world (Homer Chamber of Commerce, 2003). Maritime activity speaks for much of the economical well-being both locally in Homer, and statewide. When the water becomes too polluted to support the fishing industry, it will begin a domino effect, and another huge contributor; the tourism industry will also suffer greatly. It is important that residents make the marine environment a top priority.


One of the most dangerous and controversial contaminants today is tributyltin (TBT). Tributyltin is one of the most poisonous substances to be released to the aquatic environment today (Knutzen, 1995). The tributyltin compounds are a subgroup of the trialkyl organotin family of compounds (Extoxnet, 1996). Tributyltin is used in most of the world's marine paints to keep barnacles, seaweed, and other organisms from clinging to ships (McGinn, 2000). It is also used in wood treatment and preservation, antifungal action in textiles and industrial water systems, such as cooling tower and refrigeration water systems, wood pulp and paper mill systems and breweries (Extoxnet, 1996). In this paper, we will be discussing tributyltin in paints. Two kinds of TBT containing paints are known. Free-association paint, made by mixing TBT into the paint, dissolves when it comes in contact with 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 (Cornell University, 1993). The shipping industry has used TBT-based antifouling paints for more than 40 years to prevent hull damage and reduce drag (Lerner, 2000). Commercial vessels are the market's largest segment; with 84,000 sea-going merchant vessels weighing at least 100 gross tons. With the average life of a vessel estimated at 30 years, and the average length of a TBT self-polishing copolymer coating lasting five years, a ship needs to be coated five or six times during its lifetime (Lerner, 2000).

There are more boats in Kachemak waters than ever before. There are now an average of 1,500 boats in the summer season alone residing in the Homer Harbor, not including vessels on private shores. With the increase in boats has come an increase in the pollutants that damage aquatic life, shoreline habits, beaches and the boats themselves. Floating debris, toxic materials, garbage and sewage have both direct insidious effects. They may cause immediate harm or spread damage over many years (Smith, 1990).

Large amounts of paint containing TBT are manufactured in Norway. The Norwegian paint manufacture Jotun is one of the world's largest producers of TBT-based ship bottom paint. The largest manufacturer is International Paint (British) with a market share of 30-40%, followed by Hempel (Danish) and Jotun, each which controls 15-20% of the market (Knutzen, 1995).

Studies of the effects of TBT products on living organisms have been primarily performed on aquatic life, because TBT is mostly used in bodies of water. Thus, data gaps exist concerning effects of TBT on mammals in regard to reproduction, development and mutagenicity. In mammals, high levels of TBT can affect the endocrine glands, upsetting the hormone levels in the pituitary, gonad and thyroid glands. Large doses of TBT have been shown to damage the reproductive and central nervous systems, bone structure, and the gastrointestinal tract of mammals.

Chemicals from the paint spread into the surrounding seawater and accumulate in sediments around harbors and along shipping lanes. This is then ingested by marine invertebrates and gets into the food chain (Earth Crash, 1998). Tributyltin gradually erodes, releasing an organic tin compound. Toxic tin residues have accumulated to alarming levels in the sediments of areas with heavy boat traffic, concentrated dockage or shipyard services. 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 (Cornell University, 2003).

Effects on Crustaceans

TBT is extremely toxic to crustaceans. It has been shown that TBT contamination causes shell thickening and deformation in adult oysters (crassostrea gigas) and reduces larval success, TBT has been blamed for failures in both oyster and scallop harvests. The effects on dog whelks are very dramatic and possibly the best documented, TBT contamination causes female dog whelks to develop male characteristics (imposex) which leads to sterilization and in most cases death, males are also sterilized (Botfield, 2000). Lobster larvae show a nearly complete decrease in growth. Mollusks, used as indicators of TBT pollution because of their high sensitivity to these chemicals, react adversely to very low levels of TBT (Cornell University, 1993). The present use of tributyltin in antifouling paints may cause TBT exposure to non-target aquatic organisms such as mussels, clams, and oysters. At low levels, TBT can cause structural changes and growth retardation (Cornell University, 2003). As little as two parts per trillion of tributyltin, have caused abnormal development in oysters and clams and slowed their reproduction. Very small amounts of tributyltin, as few as two parts per trillion, have caused abnormal development in oysters and clams and slowed their reproduction (Smith, 1990). TBTs were held responsible for the near destruction of French oyster beds in the early 1980s (Lerner, 2000). Researchers at the University of Pau in Pau, France conducted studies on the organotin content of oysters and sediments from the Bay of Arachon, one of France's most productive areas for oyster farming. TBT has long been suspected as a culprit in the weakening of oyster and mussel shells (Littlehales, 2000).

Effects on Sea Otters

Crustaceans are not the only animals affected by tributyltin. A recent sea otter decline has researchers wondering if tributyltin may be to blame. Sea otters are one of the largest members of the weasel family, often even heavier than the giant otter of South America. A large male can weigh almost 100 pounds. In spite of their weight, they are virtual acrobats underwater and can stay under the surface for several minutes at a time. Sea otters are voracious eaters. To maintain their 100 degree body temperature and high metabolic rate, they eat between 20 and 30 percent their body weight a day, primarily slow-moving invertebrates such as abalone, clams, crabs, mussels and sea urchins (Bennett, 2002).

There are two populations of northern sea otters: Enhydra lutris lutris (the Russian sea otter) and the Enhydra lutris Kenyoni (the Alaskan sea otter). Recent data collected by both the Fish and Wildlife Service and the U.S. Geological Survey show that the Alaskan sea otter population in the Aleutians declined by 95% since when it numbered some 50,000 to 100,000 strong. From 1992 and 2000 they declined by 70%. Today, there are as few as 6,000 otters remaining in the entire chain (Rodman, 2003).

In a 1994 conservation plan for sea otters, the Fish and Wildlife Service (FWS) stated that preliminary data from the Aleutians suggested that TBT ratios in sea otters were unexpectedly high. These pesticides become more concentrated as they more up the food chain–a process known as bioaccumulation. FWS is presently cooperating with the Alaska Sea Otter and Sea Lion Commission to retrieve and test otter carcasses for various toxins (Bennett, 2002).

Recent tests run on dead sea otters reveal high levels of the antifouling agent tributyltin and other butyltin compounds, which most likely have contributed to immunosuppression in the sea otters and increased their susceptibility to infections (ENN, 1998). Liver samples from six sea otters have been analyzed for a group of contaminants know as the butyltins. Preliminary information indicates that there are elevated levels of these compounds in samples from otters from both Seward and Valdez, compared with those from more remote locations (U.S. Fish and Wildlife, 2002).

This is also much of a concern in California. Beginning in 1992, researchers found that infectious diseases were occurring at the unusually high rate of 40% in the California sea otter population. Unexpectedly, diseases were affecting the reproducing adult otters at this rate in addition to the very young otters (Thomas, 2001).

Sea otter extinction could trigger a devastating chain of events in the aquatic ecosystem. Without sea otters to feed on sea urchins, the sea urchin population would explode and threaten the kelp forests on which it feeds. These kelp forests are the key habitats for many other species, including fish, snails and crabs. Even sea birds, which pluck crab from the kelp forests, would eventually suffer from a burgeoning sea urchin population (AFC News Source, 2002).

Research objectives for helping the sea otters include 1) Determination of the role of infectious diseases and other mortality factors in the population's slow recovery and recent decline, 2) continued monitoring for newly emerging disease or other mortality factors, 3) examination of the health status of live otters, 4) determination of the transmission cycle of important diseases and any contributing role of contaminants, 5) identification of important sources of disease agents and contaminants, and 6) formulation of strategies to reduce disease and contaminant problems (Thomas, 2001).

Alaska's sea otters are capable of making dramatic comebacks. They were hunted nearly to extinction at the turn of the century, with numbers in the United States and Russia dwindling to about 2,000 before commercial hunting was banned in 1911. Fish and Wildlife biologists in Anchorage want to include all of southwest Alaska's sea otters as a candidate species for protection under the federal Endangered Species Act and plan to seek more funding to do so (Pemberton, 2001).

Effects on whales and dolphins

There are even more animals affected by tributyltin than just the otters and found to be heavily contaminated with tributyltin and other deep-water contaminants. This is suggesting that tributyltin has entered the deepwater food chain. Indeed tributyltin has been found in whales and dolphins from a number of locations around the world. Fish-eating toothed whales (sperm whales and killer whales), as opposed to the filter feeding whales (gray whales, humpback whales and blue whales), which feed on krill and other tiny organisms, are thought to be at higher risk due to greater bio-concentration up the food chain. Of great significance to the developing young whales is the average weight loss of 40% of their mothers' fat deposits through lactation, which may have the effect of re-mobilizing high concentrations of pollutants stored in fatty tissue. During suckling, even in filter feeding whales, the calves are effectively feeding higher up the food web and are thus even more vulnerable to contamination (Lutter, 1997).

Tributyltin poisons may also help explain recent dolphin deaths. Dolphin die-offs are frequently attributed to viruses, bacteria or parasites, suggesting outbreaks that are natural in origin. In recent years, however, scientists have assembled evidence that the real culprit in many dolphin deaths might be pollution in coastal waters. Researchers concluded that TBT and its breakdown products also lead to die-offs by suppressing dolphins' ability to fight infection. The Georgia team tested tissue from dolphins that died on or near Florida's Atlantic and Gulf coasts from November 1989 to August 1994. They found butyltins in the liver, kidney, blubber, heart, brain, and melon–an organ in the forehead that acts as a "lens" to focus sound signals for location and communication. Scientists have known for a decade that TBT is a powerful immune suppressor in marine mammals. However, until the Georgia-based study, no one had determined whether bottlenose dolphins in U.S. waters were being exposed to harmful levels of the compound. But indeed, they found higher TBT levels in bottlenose dolphins, a coastal species, than in others, which live in offshore waters. This suggests exposures from coastal shipping and painting (Schubert, 1997).

Effects on Humans

Although effects of TBT on humans are not clear, several incidents of human exposure to the biocide have been reported. Shipyard workers exposed to TBT dust and vapors while repairing a submarine developed breathing problems, irritated skin, headaches, colds, flu, fatigue, dizziness and stomach ache. TBT exposure can also irritate the eye, skin, and mucous membranes and prolonged exposure may cause liver and kidney damage (Cornell University, 1993). Human intake of organotins from seafood, especially from fish farmed in TBT-treated cages, has long been recognized. Only more recently, however, has such intake been evaluated. The residues were widely detectable in U.S. seafood but that estimated intakes were significantly below levels judged to be of concern for human health. Average intakes of TBT from seafood could lead to exceeding tolerable daily intakes based on more sensitive immunotoxicological end-points for some products retailed in North America, Europe and Asia (Santillo, 2001).

Being on the waterfront (not to mention the halibut fishing capital of the world), Homer residents' diet is perceptibly composed largely of seafood. This poses a hazard to the 12,000 residents living in and around the city of Homer because of the potential TBT intake.

Proposed TBT ban

Tributyltin manufacturers and U.S. shipbuilders lobbied against a proposal under consideration by the International Maritime Organization (IMO; London) to move up an international ban on TBT in antifouling paints (Foster, 1998). In 1988, Congress passed legislation forbidding the use of TBT paints on vessels less than 25 meters long, effectively banning their use on yachts and pleasure boats. Regulations implementing the law also limit the level of TBT in discharge waters from dry docks and repair facilities, making it difficult to use the paints on larger vessels in the US.

In March of 2000, the Alaska Legislature approved tributyltin-containing paints to be included in Senate Bill 266. Starting January 1, 2001, bottom-paints made with TBT were banned from boats of all sizes (AK Legislature, 2000). A recent research trip to Homer found that one could purchase paints containing TBT from Kachemak Gear Shed, and they'd even apply it for you. Therefore, the problem lies not in banning TBT, but in enforcing the prohibition.

Environmentalists say the use of TBT-based antifouling paints should be better enforced. The toxic effects of these chemicals on marine wildlife have been reported for more than 20 years. The only way forward lies in the development of environmentally friendly alternatives. A 1998 analysis by Princeton Economic Research Inc, Rockville, Md., indicates that existing alternative paints are up to four times more expensive than TBT-based paints (Hess, 1999). As new alternatives surface, their prices will inevitably lessen with competition.

An untreated ship can pick up 150kg of fouling every meter in less than six months. On large crude carriers with 40,000 meters under water this adds up to 6,000 tons of fouling. Fouling can cause drag and increases journey times and fuel consumption; this can be increased by between 40-50% as resistance is increased (Botfield, 2000). The cost of converting the world fleet from TBT-based paints to currently available tin-free ones is estimated at $500 million to $1 billion (Hess, 1999). This means that to convert Homer Harbor to tin-free paints is estimated to cost between $600,000 and $900,000.

Alternative products

There are many alternative products available to replace TBT, a few of which contain other biocides that can be nearly as toxic. An example of one of these brands is Irgarol, which is an atrazine biocide paired with zineb, ziram, and thiream; all of which are known pesticides and fungicides.

Before tributyltin was introduced in the early 1970's, the most commonly used antifouling paint was copper based. After the ban on TBT, many have turned back to these copper paints, in spite of the fact that copper is recognized as a harmful toxin, especially in the marine environment, where it causes severe respiratory problems, among other things. (Greenpeace, 1999)

Another alternative is a biocide free system called the "non-stick" system. After application, the hull of a ship becomes too slippery for algae, barnacles, and other marine life to attach themselves to the surface. Similar to this, a lesser-known alternative called SealCoat uses small, flexible fibers to create a velvety coating on the sides of the ship. (Greenpeace, 1999)

Micron 55 is yet another replacement for TBT based paints; based on a unique, self polishing copolymer technology which involves the constant chemical release of biocides. This product is accepted at ports all around the world, allowing ships to enter any country. (International, 2003)

Last year, the World Wildlife Fund launched an organization called the "2003 Group", which displays efficient alternatives to organotins. They showcase environmentally responsible companies within the shipping industry who already use or produce non-toxic antifouling paints without negative impact on their earnings.

Our Proposal

We believe that an alternative, non-stick paint, like Micron 55, would be the best method for solving the problem of Tributyltin killing marine animals. Micron 55 is sold in Europe for about 570.61 euros for 20 liters. Since TBT based paints are banned from boats under 25 meters long, the problem is partially solved. We need to now, either propose a ban on TBT on commercial vessels, or push the use of paints such as Micron 55. An alternative paint would benefit the marine environment without damaging Homer's marine-dependant economy. The shipping industry cannot have barnacles, mussels and other organisms sticking to the hulls of their boats because of the drag, increase in drag only makes matters worse; more gas means more pollution. So in other words, the shipping industry needs non-stick paint, but continuing to use TBT based products will only continue to harm the environment. An alternative paint is the best solution for this worldwide problem. It satisfies both worlds, Alaska's shipping industry and the marine environment.

Works Cited

Web sites

Website: ACF News Source, "Sea Otter Decline", July 9, 2002

Website: Alaska's State Legislature "Legislature Expands Ban on Toxic Paint in Alaska", March 31, 2000

Website: Botfield, Paul, Environmental Sciences Online Seminar: Group 1 Topic 4: Tributyltin Pollution, Wednesday, February 23, 2000

Website (PDF): Cornell University, Extension Toxicology Network, 5123 Comstock Hall, Cornell University, Ithaca, New York 14853-0901, 9/1993

Website: Cornish, Jim,, Gander Academy, Gander, Newfoundland, Canada, July 15, 1998.

Website: Earth Crash Earth Spirit,, 11/01/1998

Website: Environmental News Network Staff, "Ship Paints may lead to sea otter deaths" April 14, 1998

Website: Extoxnet, Extension Toxicology Network, Pesticide Information Profiles, Oregon State University,, June 1996

Website: Greenpeace, "TBT: A Global Problem for the Marine Environment", , Amsterdam, September 1999

Website: Homer Chamber of Commerce, January 2004

Website: Knutzen, J, "Environmental toxins in the ecosystem", February 1995

Website: Lutter, Stephan, "Cetaceans & Endocrine Disruptors", WWF North-East Atlantic Programme, Germany, 1997

Website: NOAA Oceans and Coasts,, April 14, 2003

Website: Rodman, Andrew, Center for Biological Diversity, Copyright 2002, July 3, 2003

Website: U.S. Fish and Wildlife Service, Marine Mammals Management,, February 15, 2000

Website: WWF (World Wildlife Fund), "International Convention on anti-fouling systems in ships, 2001", IMO Anti-fouling Convention, October/November 2001


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