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PANUPS: TBT & Dolphin Deaths

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                         P A N U P S
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                   Pesticide Action Network 
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February 3, 1997

TBT and Dolphin Deaths

In a recently released study, researchers found butyltin 
compounds, including tributyltin (TBT), in the liver, kidney 
and muscle of bottlenose dolphins that were stranded along 
the southeast U.S. Atlantic and Gulf coasts between 1989 to 
1994. Scientists are speculating that TBT and its breakdown 
products may have lead to the deaths by suppressing dolphins' 
immune systems and making them more vulnerable to disease. 

Tributyltin is an active ingredient in many products and is 
used to kill a broad range of organisms. A common use is in 
marine paint to prevent barnacles and algae from growing on 
hulls of boats and ships. By leaching into the surrounding 
water, TBT kills organisms before they can attach themselves 
to the vessels. TBT compounds are also used as disinfectants, 
wood preservatives, textile disinfectants and stabilizers in 
PVC resin.

In this recent study published in Environmental Science & 
Technology, scientists examined remains of 19 dolphins found 
beached along the Atlantic coast of Florida during 1991 to 
1994. The butyltin concentrations found in these dolphins 
were 50 to 100 fold higher than concentrations found in a 
captive adult. (The butyltin concentrations recorded in 
captive bottlenose dolphins were considered as a background 
value in cetaceans collected from Atlantic coastal areas).

Since 1987, large numbers of dead dolphins have been reported 
along the Atlantic coast of North America, in the Gulf of 
Mexico and in the Mediterranean Sea. Over 700 bottlenose 
dolphins died off the U.S. mid-Atlantic Coast in 1987 and 
1988. From February to April, 1994, 220 died on or near Texas 
beaches -- in one ten-day period, 67 were found. 

Since most incidents occurred primarily in industrialized 
coastal areas, scientists theorized that chronic exposure to 
pollutants such as polychlorinated biphenyls (PCBs) and DDT 
was responsible for these epidemics. In previous studies, 
high levels of PCBs have been documented in bottlenose 
dolphins, and researchers suggested that these high 
concentrations overwhelmed the immune systems leaving 
dolphins susceptible to infection. The results of this new 
study, however, suggest that accumulation of butyltin 
compounds also may play an important role in weakening the 
dolphins' immune systems. 

It is known that high levels of one of the most common TBT 
compounds (TBTO) can affect the endocrine system in mammals. 
High doses of TBT have also been shown to damage the 
reproductive and central nervous systems, bone structure and 
gastrointestinal tract of mammals. Studies also indicate that 
these compounds damage the immune system.

Impacts on oysters and mollusks resulting from widespread use 
of TBT as an antifouling agent in marine paints since the 
1960s have been well documented. TBT-exposed oysters in 
France and England's marine waters have been found to have 
abnormal shell development, poor weight gain, brittle shells 
and development of male characteristics in females. 

In the U.S., TBT is now regulated by the "Organotin 
Antifouling Paint Control Act of 1988." Currently, the use of 
TBT is allowed only on boats over 82 feet in length, on 
aluminum hulls over 65 feet and aluminum outdrives and 
outboard motors. France placed similar restrictions on TBT 
paints in the early 1980s; the U.K. and Ireland have similar 
legislation. There is still widespread use on large ships.

U.S. regulations limit the rate at which TBT is leached into 
the marine environment; however, according to Dr. 
Kurunthachalam Kannan, the lead researcher in this recent 
study, their results indicate that lethal amounts may still 
be reaching the ocean environment. 

Sources: "Elevated Accumulation of Tributyltin and Its 
Breakdown Products in Bottlenose Dolphins Found Stranded 
along the U.S. Atlantic and Gulf Coasts," Environmental 
Science & Technology, Volume 31, No. 1, 1997; The Dallas 
Morning News, January 20, 1997; Safer Use of Boat Bottom 
Paints, EPA, August 1989; EXTOXNET: Tributyltin, September 
1993. 
Contact: PANNA.

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