Different organizations have taken different stances on 2,4-D’s cancer risk. On August 8, 2007, the United States Environmental Protection Agency issued a ruling that stated that existing data does not support a conclusion that links human cancer to 2,4-D exposure. However, the International Agency for Research on Cancer (IARC) has classified 2,4-D among the phenoxy acid herbicides MCPA and 2,4,5-T as a class 2B carcinogen – possibly carcinogenic to humans. A 1995 panel of 13 scientists reviewing studies on the carcinogenicity of 2,4-D had divided opinions, but the predominant opinion was that it is possible that 2,4-D causes cancer in humans.
A 1990 study of farmers in Nebraska, even when adjusting for exposure to other chemicals, found that 2,4-D exposure substantially increased the risk of Non-Hodgkin’s lymphoma (NHL). A 2000 study of 1517 former employees of Dow Chemical Company who had been exposed to the chemical in manufacturing or formulating 2,4-D found no significant increase in risk of mortality due to NHL following 2,4-D exposure, but did find an increase in risk of mortality due to amyotrophic lateral sclerosis.
The amine salt formulations can cause irreversible eye damage (blindness); ester formulations are considered non-irritating to the eyes.
One study found that occupational exposure to 2,4-D caused male reproductive problems, including dead and malformed sperm.