办事指南

Indecent exposure

点击量:   时间:2019-03-08 06:15:00

By Fred Pearce 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’ hulls to kill barnacles—a practice that many governments have now partially banned. The chemical poisons whelks, causing impotence in males and a condition in females known as “imposex”, 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’s National Food Safety and Toxicology Center in East Lansing has found that most humans have butyltins in their blood. “Butyltins are toxic [in human blood] at above a few tens of parts per billion,” 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. For the first time he has also measured the damaging effect of butyltins on human “natural killer” 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 “unexpectedly high” 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 “much more immunotoxic” 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,