Chemical blamed in dolphin deaths
Researchers have found butyltin compounds, including tributyltin (TBT), in the liver, kidney and muscle of bottlenose dolphins that were stranded along the south-east US Atlantic and Gulf coasts between 1989 and 1994.
Scientists are speculating that TBT and its breakdown products may have led to the deaths by suppressing the dolphins' immune systems.
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. TBT compounds are also used as disinfectants, wood preservatives, textile disinfectants and stabilisers in PVC resin.
In this recent study, published in Environmental Science & Technology, scientists examined remains of 19 dolphins. The butyltin concentrations in these dolphins were 50 to 100 times higher than concentrations found in a captive adult.
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. More than 700 bottlenose dolphins died off the US mid-Atlantic coast in 1987 and 1988. From February to April 1994, 220 died on or near Texas beaches — in one 10-day period, 67 were found.
In previous studies, high levels of polychlorinated biphenyls (PCBs) have been documented in bottlenose dolphins, and researchers suggested that these high concentrations overwhelmed the immune systems, leaving dolphins susceptible to infection. This new study, however, suggests that accumulation of butyltin compounds may also play an important role in weakening the dolphins' immune systems.
It is known that high levels of one of the most common TBT compounds 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.
In the US, currently, the use of TBT is allowed only on boats over 82 feet (25 metres) in length, on aluminium hulls over 65 feet and aluminium outboard motors. France, Britain and Ireland have similar legislation. There is still widespread use on large ships.
[From Pesticide Action Network North America Updates Service.]