Cottonwood Clues in Fallon: Tree Rings Reflect Tungsten, Cobalt Exposure

Article excerpt

The cause of a childhood leukemia cluster in Fallon, Nevada (population 8,000) has mystified investigators since it was first discovered in 2000. Sixteen children have been diagnosed with acute lymphocytic leukemia and one with acute myelocytic leukemia. Because known risk factors such as ionizing radiation and prenatal exposure to volatile organic compounds do not explain most acute lymphocytic leukemia cases, researchers suspect other environmental exposures in Fallon. Now a tree ring study reveals elevated environmental tungsten and cobalt levels in Fallon compared to other towns in the area in the years just prior to the onset of the cluster [EHP 115:715-719; Sheppard et al.].

Among Fallon's potential sources of contamination are a tungsten carbide production facility, melon and alfalfa fields, and a naval air base jet fuel pipeline. The study team took core samples representing the years 1989 through 2002 from cottonwood trees around the Fallon processing plant and analyzed them for tungsten, cobalt (also used in tungsten carbide processing), and a range of other metals. For comparison, they also sampled trees in three nearby towns. In addition, the team tested trees in Sweet Home, Oregon, which also has a known local source of airborne tungsten, to test the dendrochemical technique independently. …