In a move not seen for almost 40 years, the Environmental Protection Agency on Tuesday issued an emergency order suspending all uses of a weedkiller linked to serious health risks for unborn babies.

The herbicide dimethyl tetrachloroterephthalate, also known as DCPA or Dacthal, is used on crops such as broccoli, brussels sprouts, cabbage and onions. Fetuses exposed to it could suffer from low birth weight, impaired brain development, decreased I.Q., and impaired motor skills later in life, the E.P.A. said.

“DCPA is so dangerous that it needs to be removed from the market immediately,” Michal Freedhoff, the E.P.A. assistant administrator for the Office of Chemical Safety, said in statement. “In this case, pregnant women who may never even know they were exposed could give birth to babies that experience irreversible lifelong health problems.”

California-based AMVAC Chemical Corporation, the sole manufacturer of the pesticide, didn’t immediately respond to a request for comment.

Tuesday’s order followed several years of “unprecedented efforts” by the Environmental Protection Agency to get AMVAC to submit its own data on the pesticide and its health risks, the agency said. The agency estimates that pregnant women handling DCPA products could be subjected to exposures four to 20 times greater than what E.P.A. has estimated is safe for fetuses.

Mily Treviño Sauceda, executive director of Alianza Nacional de Campesinas, also known as the National Farmworkers Women’s Alliance, called E.P.A.’s decision “historic.”