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 The classification of the weed killer, 2,4-dichlorophenoxyacetic
acid, known as 2,4-D, was made by the WHO's International Agency for
Research on Cancer (IARC).
The IARC said it reviewed the latest scientific literature and
decided to classify 2,4-D as "possibly carcinogenic to humans." That
is a step below the more definitive "probably carcinogenic" category
but two steps above the "probably not carcinogenic" category.
IARC's findings on 2,4-D have been awaited by environmental and
consumer groups that are lobbying U.S. regulators to tightly
restrict its use, as well as by farm groups and others that defend
2,4-D as an important agent in food production that does not need
more restrictions.
Since its introduction in 1945, 2,4-D has been widely used to
control weeds in agriculture, forestry, and urban and residential
settings.
In March, IARC said it had found another popular herbicide -glyphosate
- was "probably carcinogenic to humans." Glyphosate, the world's
most widely used weed killer, is the key ingredient in Monsanto Co's
Roundup herbicide and other products.
IARC classifications do not carry regulatory requirements but can
influence regulators, lawmakers and the public. Following the
glyphosate classification, some companies and government officials
moved to limit glyphosate use.
Dow AgroSciences, a unit of Dow Chemical Co, has had a particular
interest in IARC's review. The company is using both glyphosate and
2,4-D in a herbicide it calls Enlist Duo that received U.S. approval
last year. Enlist Duo is designed to be used with genetically
engineered, herbicide-tolerant crops developed by Dow.
Dow said in a statement that IARC's classification was flawed and
was "inconsistent with government findings in nearly 100 countries"
that have affirmed the safety of 2,4-D when used as labeled.
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IARC said it decided on the "possibly carcinogenic" classification
because there was "inadequate evidence in humans and limited
evidence in experimental animals" of ties between 2,4-D and cancer.
It said that epidemiological studies provided "strong evidence that
2,4-D induces oxidative stress ... and moderate evidence that 2,4-D
causes immunosuppression."
However, IARC said, "epidemiological studies did not find strong or
consistent increases in risk of NHL (non-Hodgkin lymphoma) or other
cancers in relation to 2,4-D exposure."
Dana Loomis, a deputy section head for IARC, said the most important
studies reviewed showed mixed results, and a "sizable minority"
judged the evidence as stronger than others did.
Among the research presented to IARC was an analysis funded by a
Dow-backed task force that found no ties between 2,4-D and many
cancers.
Some critics of 2,4-D had expected IARC to classify 2,4-D as
"probably" cancer-causing. But the classification it did receive
still underscores the dangers of 2,4-D and the need for a "much more
rigorous regulatory process," the Pesticide Action Network North
America said in a statement.
(Reporting by Carey Gillam; Editing by Steve Orlofsky and Leslie
Adler)
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