OUR bodies may contain significant amounts of a type of pollutant known to
endow female dog whelks with a penis. The scientists who have discovered these
toxic chemicals in routine tests of human blood and organs fear they could
reduce our ability to fight cancers.
Butyltins, including the shellfish sex-change agent tributyltin, is applied
to ships鈥� hulls to kill barnacles鈥攁 practice that many governments have
now partially banned. The chemical poisons whelks, causing impotence in males
and a condition in females known as 鈥渋mposex鈥�, in which they grow a penis.
The chemicals are also found in everything from chocolate wrappers to
household paint. Often they are added to kill moulds such as mildew and other
infestations, they are used as a catalyst in making the silicones that coat
baking paper, and act as stabilisers in plastics such as PVC. Reports that they
are present in a wide variety of food and drinks emerged in the early 1990s. Now
Kurunthacalam Kannan of Michigan State University鈥檚 National Food Safety and
Toxicology Center in East Lansing has found that most humans have butyltins in
their blood. 鈥淏utyltins are toxic [in human blood] at above a few tens of parts
per billion,鈥� says Kannan. In two studies reported in recent weeks, he found
individuals whose blood contained levels of butyltin well above this safety
limit at between 100 and 155 parts per billion.
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For the first time he has also measured the damaging effect of butyltins on
human 鈥渘atural killer鈥� white blood cells, which fight tumours and viruses. In a
forcoming issue of Environmental Research, he will report on laboratory
experiments which show that butyltins at levels only a little above those found
in routine blood samples inhibit the tumour-killing capacity of these cells by
up to 90 per cent.
His concerns have been underlined by Shinsuke Tanabe of the environment
conservation department at Ehime University in Matsuyama, Japan. Tanabe is about
to report in the journal Environmental Pollution his finding that human
livers can contain up to 100 parts per billion of butyltin compounds.
The studies suggest that people frequently experience an 鈥渦nexpectedly high鈥�
exposure to the chemicals, says Kannan. He speculates that as a result, some
people may be at increased risk of cancer.
Kannan accuses bodies that fund medical research of being slow to respond to
the threat posed to human health by butyltins. He says it has been easy to raise
funds for research into the effects of butyltins on marine mammals such as seals
and dolphins, while funding for work on humans has been harder to find.
Both dibutyltin and tributyltin are 鈥渕uch more immunotoxic鈥� than PCBs, Kannan
says. Tanabe will report later this year that he believes a series of mass
deaths among marine mammals in European and American waters in the past decade
may have been due to butyltin poisoning, rather than to PCBs, as previously
suspected. Butyltin levels in affected porpoises and dolphins were between 10
and 100 times the highest levels so far seen in people, he says.