The U.S. Environmental Protection Agency (EPA) has issued an emergency notice pulling the pesticide dimethyl tetrachloroterephthalate, also known as DCPA or Dacthal.

The chemical was placed under an emergency order to stop further use, the first order of its kind in nearly four decades, because of the risk it poses to fetuses in pregnant people. According to the EPA, when pregnant people are exposed to DCPA, it can change the fetal thyroid hormone levels.

After birth, the baby may experience low birth weight, impaired brain development and decreased IQ, the agency warned. Later in life, the exposure could also be linked to impaired motor skills. The EPA noted that some of the effects of exposure could be irreversible.

“DCPA is so dangerous that it needs to be removed from the market immediately,” Michal Freedhoff, assistant administrator for the EPA’s Office of Chemical Safety and Pollution Prevention, said in a statement. “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. That’s why for the first time in almost 40 years, EPA is using its emergency suspension authority to stop the use of a pesticide.”

The pesticide is commonly used on broccoli, cabbage, onions, strawberries and Brussels sprouts to mitigate weeds, although it has other agricultural and non-agricultural uses.

Exposure to DCPA is often unknown because of how long it can remain at levels considered unsafe. The EPA explained that DCPA product labels say to wait 12 hours after applying before entering treated areas, but there was evidence that DCPA levels remain high for at least 25 days after application. Wind can also carry the pesticides further from the applied area, exposing more people.

The emergency ban follows years of review and studies on the potential impacts of DCPA exposure. The EPA first requested more information on the chemical from its sole manufacturer, AMVAC Chemical Corporation, in 2013. The request called for 20 or more studies, but the EPA said that the corporation’s provided data from 2013 to 2021 was “insufficient” and that certain requested studies, including a study on the effects of DCPA exposure on thyroid development, were never submitted.

Following an EPA warning of intent to suspend the registration of the pesticide in April 2022, AMVAC Chemical Corporation provided a thyroid study later the same year. The EPA then followed up with an assessment of the study in 2023, highlighting health concerns with DCPA exposure.

^{An advertisement for Dacthal in Time Magazine on March 23, 1962. SenseiAlan / CC BY 2.0}

As USA Today reported, concerns over DCPA were first brought about by the Environmental Working Group (EWG) in the 1990s. At the time, the pesticide was commonly used on turf. AMVAC Chemical Corporation voluntarily canceled most turf-related uses of DCPA in December 2023.

In 1998, the EPA issued a fact sheet on DCPA that said the pesticide was classified as a possible human carcinogen following development of thyroid tumors in rats after DCPA exposure.

The EPA issued the emergency order for DCPA via the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA) and stated that although the manufacturer has addressed concerns over the pesticide, “there are no practical mitigation measures that can be put in place to allow DCPA’s continued use.”

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