to public concern over dioxin and nitrosamine contamination in 2,4-dichlorophenoxy
acetic acid (2,4-D), several recent studies show that this pesticide can
cause lymphatic cancer in exposed humans. 2,4-D is the most widely used
herbicide in the non-agricultural sector with 23-27 million pounds used
annually (U.S. EPA 1999). All 2,4-D products are required to carry the
DANGER signal word on the label indicating its EPA toxicity rating of
I, the highest of four categories. The U.S. Environmental Protection Agency
(EPA) has not fully evaluated 2,4-D’s effects on human health and the
findings on carcinogenicity add to the already incriminating body of evidence
on 2,4-D, including a manufacturers’ study submitted to EPA in June 1986,
indicating the herbicide, which is widely used in agriculture, forestry
and urban settings, can cause rare brain tumors (astrocytomas) in rats.
These studies indicate a need for closer examination of other commonly
used phenoxies such as dichlorprop, mecoprop (MCPP), MCPA and 2,4,5-T
(banned in the U.S.).
1988 National Cancer Institute (NCI) study, conducted by Drs. Sheila Hoar
and Aaron Blair, examined all cases of diagnosed cancer among Kansas farmers
between 1976 and 1982. According to the study, farmers who were exposed
to 2,4-D for 20 or more days per year had a sixfold higher risk of developing
non-Hodkin’s lymphoma than non-farmers, while farmers who mixed or spread
the herbicide had an eightfold higher risk of developing the tumor. Significantly,
the researchers noted that farmers who took precautions to minimize their
exposure were at lesser risk (Hoar-Zahm 1988).
Dr. Hoar also published a 1990 study of Nebraska farmers which
demonstrates a 50% increase in non-Hodgkin’s lymphoma for growers who
handle 2,4-D. The linkage between 2,4-D exposure and non-Hodgkin’s lymphoma
has also been documented in Sweden, Canada, Nebraska and Washington (Zahm
a 1991 NCI study found that dogs whose owners’ lawns were treated with
2,4-D four or more times per year were twice as likely to contract canine
malignant lymphoma than dogs whose owners did not use the herbicide. Malignant
lymphoma in dogs is considered very similar to non-Hodgkin’s lymphoma
in humans (Hayes 1991).
addition to these studies, a bioassay conducted by the Food and Drug Administration
found increased incidences of lymph sarcoma (malignant tumors) in both
male and female rats, breast tumors in female rats and reticulum cell
sarcoma (malignant blood cell tumors) in male rats exposed to 2,4-D. The
latter were also found in mice exposed to the iso-octyl salt of 2,4-dichlorophenol,
major breakdown product, to be a cancer promoter.
with all the mounting evidence, EPA has listed 2,4-D as a Group D chemical
for its carcinogenic potential. Chemicals in the classification category
represents chemicals with inadequate human and animal evidence of carcinogenicity
or for which no data are available (U.S. EPA 2000).
to EPA, 2,4-D is irritating to the eyes, skin and mucous membrane and
since it is easily absorbed dermally or by inhalation, can injure liver,
kidney, muscle and brain tissues. Acute symptoms of exposure include:
chest and abdominal pain, vomiting, dizziness and muscle twitching, tenderness
or stiffness (U.S. EPA 1982). Studies in rats have demonstrated that 2,4-D
can migrate into nervous tissue and concentrate in certain areas of the
brain. Not too surprisingly, behavioral changes have also been observed
in treated rats (Evangelista de Duffard 1990). In humans, seemingly minor
dermal exposures have bee known to cause peripheral neuropathy (irreversible
loss of feeling in the extremities). Depression, lethargy and coma have
also been documented in animals and humans.
is also a mutagen. In laboratory tests it has mutagenic effects on human
lymphocytes and human fibroblasts. Genotoxicity has even been documented
in plants. Reproductive toxicity has been observed in animals at high
dose levels. Exposure resulted in fetuses with abdominal cavity bleeding,
increased mortality and inhibition of DNA synthesis in the testes (ETN
1996). A study of male farmers also demonstrated reduced sperm counts
and sperm abnormalities in 2,4-D exposed farmers, and abnormalities were
still apparent even one year after exposure.
is slightly toxic to wildfowl (mallards, pheasants, quail and pigeons),
while some formulations are highly toxic to fish. Moderate doses of the
chemical fed to honeybees caused severe impairment of blood production.
reports show that amine salt formulations of 2,4-D may become contaminated
during synthesis with up to several hundred parts per billion of nitrosamines,
known to be potent carcinogens. Several forms of dioxin have been identified
in 2,4-D, including 2,3,7,8-tetrachlorodibenzo-p-diozin (also known as
TCDD, the most toxic of the dioxin family, at levels greater than one
part per billion); 1,3,7,9 and 1,3,6,8-TCDD; 2,7-dichlorodibenzo-p-dioxin;
and 1,2,4- and 1,3,7-trichlorodioxins. The dioxins can cause cancer, birth
defects, reproductive effects, liver damage and chloracne. Other contaminants
include 1,3,6,8-tetrachloroxanthone (TCX) and 2,4-dichlorophenol.
systemic herbicide, 2,4-D is easily absorbed by foliage and translocated
throughout the treated plant, which dies in 7-14 days. Phenoxy acid herbicides
like 2,4-D mimic the action of natural plant growth regulators known as
auxins, causing treated plants to literally grow themselves to death.
In soil, 2,4-D residues usually dissipate within a month, primarily due
to microbial degradation). 2,4-D is known to leach from soils low in clay
or organic content and in cool, dry, nutrient-poor soils. Under these
conditions, residues may persists for several months.
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2,4-dichlorophenoxyacetic butyl ester during chick embryonic development.”
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