Panel weighs health impact of herbicides.

The National Academy of Sciences' Institute of Medicine (IOM) this week released a report that finds a statistical link between three cancers, two other disorders, and exposure to chemicals in herbicides used during the Vietnam War.

U.S. troops sprayed nearly 19 million gallons of herbicides over about 4 million acres in Vietnam between 1962 and 1971. The herbicides defoliated large areas of thick jungle, thus enabling U.S. military forces to scan for enemy troops. Concerns about the health effects of herbicides, such as the dioxin-tainted Agent Orange, first surfaced in 1970. Since that time, the debate over the health effects of herbicides has been clouded by scientific uncertainty, politics, and a maelstrom of strong emotions.

The 16-member IOM panel of epidemiologists, toxicologists, and other experts stepped into the fray after Congress passed a law calling for a review of the existing scientific evidence on the possible health effects caused by exposure to herbicides. The panel issued the report, "Veterans and Agent Orange," at a July 27 press conference held in Washington, D.C.

"For the very first time, veterans and the American public have a solid reason to believe that their concerns about exposure to Agent Orange, dioxin, and other toxic chemicals are at long last being taken seriously," said Sen. Thomas Daschle (D-S.D.) at a hearing of the Senate Committee on Veterans' Affairs, held the same day to review the IOM report.

The panel found strong evidence of a statistical association between herbicides or dioxin and soft-tissue sarcoma, non-Hodgkin's lymphoma, and Hodgkin's disease, three types of cancer. The panel's review also turned up substantial evidence of a link between herbicide exposure and chloracne, an acne-like skin disorder, as well as porphyria cutanea tarda, a liver disorder that causes skin blistering.

The government acted quickly on those findings. At the Senate hearing, Secretary of Veterans Affairs Jesse Brown announced that Vietnam veterans with Hodgkin's disease and porphyria cutanea tarda will now be entitled to disability payments based on their service in Vietnam and their exposure to herbicides. The VA already compensates veterans suffering from non-Hodgkin's lymphoma, soft-tissue sarcoma, and chloracne.

The IOM panel reviewed data from 230 epidemiological studies. Most of the studies focused on people who reported on-the-job contact with the chemicals in herbicides or people exposed as a result of an industrial accident. They generally did not include Vietnam veterans, whose exposure to herbicides has been difficult to document. The panel acknowledged that limitation but said its review suggests that people (including Vietnam veterans) who come in contact with these chemicals run a risk of developing the three cancers and two other diseases.

"How big that risk is quantitatively, we just don't know," says IOM panel member David Kriebel, an occupational epidemiologist at the University of Massachusetts at Lowell.

The IOM panel also found hints of a weaker association between exposure to herbicides and lung and throat cancers, prostate cancer, and multiple myeloma, a cancer of the bone marrow. However, the group says the observed link could result from chance or bias.

A raft of disorders fell into a gray zone in which the panel concluded that available studies were not of sufficient quality or did not have the statistical power to warrant any conclusions. These health problems include immune disorders, renal cancer, leukemia, birth defects, and infertility

Finally, the IOM committee sifted through the evidence and concluded that there appeared to be no connection between herbicide exposure and skin cancer, bladder cancer, brain tumors, or gastrointestinal tumors such as stomach cancer.