Abandoning an earlier conclusion, an Institute of Medicine (IOM) panel now says there is no link between Agent Orange and a form of leukemia in the children of Vietnam veterans exposed to the pesticide. In a report released today, the panel says that a combination of finding new evidence and identifying an earlier error led to the revamped conclusion, which contradicts a report from the same panel nearly a year ago.
Agent Orange, a code name for an herbicide designed to strip trees of foliage and thereby expose enemy troops, was widely used during the Vietnam war. Concerns over long-term health risks stemming from exposure to the compound prompted Congress in 1991 to ask the National Academy of Sciences (NAS) to review potential health problems in veterans and their children. Since then, IOM, a division of NAS, has released several studies, including a 2000 report postulating a link between Agent Orange and acute myelogenous leukemia (AML) in the children of exposed veterans.
But shortly after releasing that report, the authors learned of a problem: A study of Australian veterans on which they had relied heavily contained an error. The flaw, uncovered by that study's authors, negated its conclusion that children of veterans faced a greater-than-average risk of AML. Meanwhile, new data surfaced. Some researchers analyzed AML cases in Germany and found no evidence that children of men exposed to other pesticides were more likely develop the disease. A comparable study in Norway that examined the children of farmers exposed to pesticides, including herbicides, arrived at a similar conclusion. "We don't have a smoking gun here," said Tee Guidotti, a panel member and chair of the department of environmental and occupational health at George Washington University Medical Center in Washington, D.C.
Other scientists agree that a link now appears much less likely, although novel work could still uncover one. "Any sizable effect seems to be ruled out," says Gilbert Omenn, a geneticist and public health researcher at the University of Michigan, Ann Arbor. Epidemiologist Andrew Olshan of the University of North Carolina, Chapel Hill, notes that risks from Agent Orange are notoriously tough to analyze, because it's difficult to determine the intensity and duration of exposure.