Sheppard, who works in dendrochemistry, was intrigued. He suggested combining tree-ring studies with air sampling.
The tree corers are hardened steel, so he had to figure out how to eliminate potential contamination. Sheppard eventually used laser trimming, as is used for decorative metal mailbox flags, to cut away a thin layer all around each pencil-sized tree core.
The annual rings then were analyzed for heavy metals.
To verify that differences in airborne tungsten could be detected using tree rings, the team tested trees close to and distant from a known source of airborne tungsten in Oregon.
Cores taken from trees close to that tungsten source had more tungsten than cores taken from more distant trees. Few residences and schools are located near the Oregon site.
In Fallon, the team reports finding elevated tungsten levels in about a 1.8 mile (three kilometers) radius that includes residences and schools. According to a February 2003 U.S. Health and Human Services report, (http://www.atsdr.cdc.gov/HAC/PHA/fallonair/finalair.pdf), Fallon has a facility that "houses offices, a laboratory and a tungsten carbide processing operation."
The International Agency for Research on Cancer has declared cobalt and tungsten carbide together to be a probable carcinogen. (http://monographs.iarc.fr/ENG/Meetings/vol86.php)
The biological research that has been done suggests a relationship between tungsten and cobalt and cancer but is not definitive, the researchers write.
Witten said, "There needs to be more research done to examine the relationship between these metals and the development of leukemia. We're doing
Contact: Mari N. Jensen
University of Arizona