Trees link leukaemia clusters
Ring study hints that childhood cancer could be connected to tungsten.
Three different clusters of childhood leukaemia in the western United States may be linked to high levels of tungsten in the environment, a new study hints.
In the past five years, 17 children have developed leukaemia in the small mountain town of Fallon, Nevada, home to just 2,383 kids under 18. "This is much higher than the expected rate of 4.2 cases of leukaemia for every 100,000 kids over a five-year period," says Paul Sheppard of the University of Arizona in Tucson.
Sheppard has analysed trees in the Fallon area. Trees record information about environmental conditions in their annual growth rings. Sheppard compared metal concentrations in rings for the past five years with those from a five-year period during the 1980s when leukaemia rates were normal.
He found that tungsten levels had risen and that there was no detectable change in the level of any other metal. The trees in two other towns with high rates of childhood leukaemia - Sierra Vista, Arizona, and Florin, California - also show increased tungsten levels over the past five years, Sheppard told this week's annual meeting of the American Geophysical Union in San Francisco, California.
A recent study in Fallon by the Centers for Disease Control and Prevention (CDC) found higher-than-average levels of tungsten in tap water and urine. Consequently, the CDC recommended that residents avoid drinking tap water. Sheppard found increased levels of tungsten in the air in Sierra Vista. Both of these towns are close to old tungsten mines, but the cause of the rising tungsten levels is still unknown.
To date, the US Environmental Protection Agency has not identified tungsten as a potentially cancer-causing agent - very little research has been done on the metal's biological effects. But at least one study has linked it to tumor-like changes in cells, says Mark Witten, a paediatric toxicologist at the University of Arizona who participated in the research.
Sheppard and Witten have just received a US$140,000 grant to continue their study from the Gerber Foundation, a private charitable organization based in Fremont, Michigan, that is committed to children's issues.
Witten plans to expose mice to the levels of tungsten found in Fallon and see whether they develop leukaemia. He will also carry out urine tests in Sierra Vista and Florin. Sheppard will continue to study tree rings in the three towns and compare the tungsten concentrations with those of trees in nearby areas without cancer clusters.
American Geophysical Union Meeting,
San Francisco, December 2003
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