Re: Cha^'t ddo^.c ma`u da cam

["Toan" <toan@usa.net>]

To^i lu+o+.m ca'i na`y ve^` tu+` National Cancer Institute, Oncolink:
<http://cancer.med.upenn.edu/pdq_html/6/engl/600322.html>

In Answer to Your Questions About Agent Orange 

Agent Orange was a mixture of herbicides used between 1963 and 1971 during
the Vietnam War. Named for the orange-striped containers in which it was
stored, Agent Orange was employed mainly to defoliate forest trees. It also
was used to destroy the enemy's crops. Agent Orange contained two
chlorophenoxy herbicides: 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) and
2,4-dichlorophenoxyacetic acid (2,4-D). These herbicides were first used in
the United States in the mid-1940s to control broadleaf weeds in cereal
grain fields, pastures, and turf. They also were used to remove unwanted
plants from rangeland, forests, noncropland, and waterways. By the
mid-1960s, chlorophenoxy herbicides had become the most important class of
herbicides in the United States. 

During the 1970s, health concerns about the herbicides brought about
Government restrictions that caused a sharp decrease in the manufacture and
use of 2,4,5-T. Since 1983, the use of 2,4,5-T has been prohibited in the
United States. Many other countries also have ended its use. Of additional
concern is a contaminant commonly called dioxin
(2,3,7,8-tetrachlorodibenzo-p-dioxin, or TCDD), which often forms when
2,4,5-T is manufactured. Of the approximately 75 chemicals in the dioxin
family, TCDD is the most toxic. It can cause chloracne, a skin disease, and
is suspected to cause some kinds of cancer. The TCDD level in Agent Orange
varied from 0.02 to 54 micrograms per gram of 2,4,5-T. 

Farmers, forestry workers, and Vietnam veterans exposed to chlorophenoxy
herbicides have been studied to see whether they had a higher incidence of
cancer than would be expected. The results of these studies have been
conflicting and inconclusive. 

In 1984, Congress mandated that studies be conducted to determine whether
service in Vietnam could be related to adverse health effects. In one
study, scientists investigated the long-term health effects of military
service in Vietnam; another study focused specifically on the health
effects of exposure to Agent Orange in Vietnam; and a third study looked at
the increased risk, if any, that Vietnam veterans would develop any of six
specific kinds of cancer. 

In March 1990, the Centers for Disease Control and Prevention (CDC)
released the results of the last of its studies. The investigators reported
a 50-percent higher incidence of non-Hodgkin's lymphoma (NHL), a cancer of
the immune system, among Vietnam veterans than among veterans who did not
serve in Vietnam. However, the studies could not show that this increased
incidence is related to exposure to Agent Orange. For example, Navy
veterans who served on vessels off the coast of Vietnam tended to have a
higher rate of NHL than did veterans based on land, and veterans who served
in the region of heaviest Agent Orange use tended to have a somewhat lower
incidence than veterans who served in other regions of Vietnam. The CDC
could not determine why the Navy veterans had an increased incidence of
NHL. No increased incidence was found for the other five cancers in the
study (soft tissue and other sarcomas, Hodgkin's disease, and nasal,
nasopharyngeal, and liver cancers). 

Following the release of the results of the CDC studies, the Secretary of
the Department of Veterans Affairs (VA) announced that VA would begin
awarding compensation to Vietnam veterans with NHL. Vietnam veterans with
NHL will receive monthly disability payments for the rest of their lives. A
short time later, it was announced that Vietnam veterans with soft tissue
sarcomas are eligible for disability payments even though the CDC studies
failed to show that they are at increased risk for this kind of cancer.
Vietnam veterans suffering from chloracne and peripheral neuropathy, a
nerve disease, also are eligible for benefits. The VA recently stated that
no connection between exposure to Agent Orange and the development of lung
cancer has been shown and denied disability benefits for Vietnam veterans
with this disease. 

In 1990, National Cancer Institute researchers reported the results of a
study showing an increased risk of testicular tumors in military working
dogs who served in Vietnam during the conflict there. Because the
carcinogenic (cancer-causing) risk to dogs can be a useful indicator of
carcinogenic risk to humans, another study was initiated to determine
whether Vietnam service led to an increased risk of testicular cancer in
humans. The results of this study showed a twofold increased risk of
testicular cancer in Vietnam veterans. However, identification of specific
factors, such as exposure to Agent Orange, could not be implicated as the
cause of this increase. 

For additional information about Agent Orange, contact:
Centers for Disease Control and Prevention
1600 Clifton Road NE
Mail Stop F16
Atlanta, GA 30333
404-488-4460


U.S. Department of Veterans Affairs
Environmental Medicine Office
1-46A
810 Vermont Avenue NW
Washington, DC 20420
202-535-8175


Disabled American Veterans
807 Maine Avenue SW
Washington, DC 20024
202-554-3501