The last emergency ban of this kind was of the pesticide ethylene dibromide, or EDB, in 1983.
Dacthal is used to control weeds in agricultural and non-agricultural settings, the EPA says. It's commonly applied to grasses, artificial turf, crops including strawberries, cotton and field beans and vegetables such as broccoli, Brussels sprouts, cabbage and onions.
The agency cited "serious risks" to unborn babies of pregnant women who are exposed to the chemical including living in or around areas where Dacthal has been used. Some pregnant people who handle DCPA products could be exposed to levels that are four to 20 times higher than what the EPA considers safe for unborn babies.
Although product labels advise restricted entry into fields for 12 hours after application, there is evidence that DCPA levels may remain unsafe for 25 days or more, the agency said.
Exposure can alter fetal thyroid hormone levels, a change linked to low birth weight, impaired brain development, decreased IQ and impaired motor skills later in life, according to the EPA.
"DCPA is so dangerous that it needs to be removed from the market immediately," Michal Freedhoff, assistant administrator for the agency's Office of Chemical Safety and Pollution Prevention, said in a news release. "It's EPA's job to protect people from exposure to dangerous chemicals. In this case, pregnant women who may never even know they were exposed could give birth to babies that experience irreversible lifelong health problems."
Issues with Dacthal were flagged in 2013 after the EPA called on AMVAC Chemical Corp. - the sole producer of Dacthal - to submit evidence supporting its continued registration for human use. Much of the research submitted was deemed insufficient, and key studies, including those on thyroid effects, were missing. Despite AMVAC's later compliance and voluntary cancellation of Dacthal on artificial turf, the EPA found the risks "unacceptable" and changes the company proposed as "not adequately addressing the serious health risks for people who work with and around DCPA."
In September, the EPA suspended the product after AMVAC failed to submit data to support its continued registration. In April, the agency further warned farmworkers, specifically pregnant women, about risks of Dacthal.
Tuesday's emergency order is effective immediately, and the EPA intends to issue a notice of intent to cancel DCPA products within the next 90 days, according to the warning.
AMVAC did not respond to CNN's request for comment.
Mily Treviño Sauceda, executive director of Alianza Nacional de Campesinas, the National Farmworkers Women's Alliance, said in the EPA's news release that the organization is pleased about the "historic decision."
"As an organization led by farmworker women, we know intimately the harm that pesticides, including dimethyl tetrachloroterephthalate (DCPA or Dacthal), can inflict on our bodies and communities. This emergency decision is a great first step that we hope will be in a series of others that are based on listening to farmworkers, protecting our reproductive health, and safeguarding our families."
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