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Toxic pesticide TBT poisons worldwide marine wildlife; used widely on hulls of oil tankers

Tuesday, December 27, 2005 by: Dawn Prate
Tags: TBT, tributyltin oxide, marine life

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There is something picturesque about a ship bobbing up and down against a blue swell of waves and settling into a harbor to unload its cargo. Equally picturesque are the kinds of wildlife navigating underneath: Fish and shellfish scurrying about the colorful blooms of coral, piles of oysters and larger mammals, like whales and dolphins, swimming to and fro. This picture of the oceanic ecosystem is serene, almost quiet. Unfortunately, the reality of our modern marine ecosystem is far different.

For 40 years, oceanographers and fishermen have warned governments of certain marine technologies destroying the vast biota underwater. In the most recent case of environmental destruction, the culprit comes in the form of strong chemicals painted on the hulls of ships to protect from pests. Tributyltin oxide (TBT), an organotin compound, is the active ingredient in these marine paints. TBT prevents the growth of algae, barnacles and other marine organisms on the ship's hull, but, like most pesticides, these chemicals kill much more than just their targets.

TBT was first used in the 1960s as an antifouling biocide, but signs of its destructive properties didn't emerge until the 1970s. In both Europe and the United States, studies began to show rapid decimation of marine life in harbors and other high-traffic areas. The American mud-snails, dogwhelks, oysters and other mollusk populations were all in decline by the early 1970s. Shellfish were found suffering from impaired immune systems, shell deformities and a condition called imposex, in which male sexual organs appear on female mollusks.

Unfortunately, the link between these conditions and TBT was not immediately apparent. Only in the 1980s, using advanced analytical and technological instrumentation to measure TBT distribution, could scientists link these deformities directly to TBT levels. In 1986, one study of Plymouth Sound proved that increases of imposex strongly coincided with TBT applications. In 1989, studies found that the use of TBT paints on salmon-farming cages resulted in contamination of a Scottish sea loch, as well as higher incidence of imposex.

As the evidence mounted against TBT, governments slowly began to establish regulations. France, suffering huge losses in the oyster industry, was the first country to limit the use of TBT. In 1982, the French government placed controls on the application of TBT paints to vessels under 25 meters in length. (These small vessels usually spend most of their time around harbors where oyster populations could be severely effected). In 1987, the UK went one step further, banning all retail sale of TBT paint for smaller vessels. As usual, the United States was slowest to take action, introducing a similar ban in 1988.

Unfortunately, these restrictions and bans did not take into account sea-going vessels. While many of the shellfish populations partially recovered in harbors and bays, TBT dangers were by no means eliminated. The increase in commercial vessels, especially oil tankers and military vessels (both using unregulated amounts of TBT paint), has had measurable effects on marine ecosystems.

During the mid-1990s, a number of studies introduced new harms caused by TBT. This time, the effects of TBT were not limited to smaller marine life in harbors. Scientists found dangerous accumulations of butyltin in dolphins, tuna and sharks in the Mediterranean seas. A later study linked these levels to immune dysfunction. In 1997, a study linked high levels of TBT in the bottlenose dolphin to their abnormal rates of mortality reported on the U.S. Atlantic and Gulf coasts. Greenpeace also reported that TBT was been found in the tissues of cetaceans, seals, sea otters and water birds in a wide range of locations around the world.

Most startling, however, is evidence that dangerous amounts of TBT and its breakdown products accumulate in the bodies of sperm whales. This indicates that TBT may be widely dispersed in the marine environment, including the deep oceans where sperm whales normally live and feed.

In a recent study at Yale University, researchers found that TBT could cause hearing difficulties in whales and other mammals. Prestin, a protein essential to whale cochlear amplification (the amplification of sounds by tiny hairs) is severely affected by TBT levels. By hindering the mechanical activity of the outer hair cells, which boost incoming sound to the whales, TBT effectively cripples whales' auditory amplification and sensation. Because whales rely on their sensitive hearing apparatus for motor activity, damage to their ears could alter, if not annihilate, populations in some areas.

Current efforts are under way by Greenpeace and other marine environmental groups to push the government to restrict TBT use even further, if not outlaw the pesticide outright. Until then, marine populations will continue to be threatened by these toxic pesticides that remain perfectly legal to use on the hulls of oil tankers and other ships that traverse the oceans of our planet.

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