Due to the adverse health effects associated with exposure to dimethyl tetrachloroterephthalate (DCPA), commonly known as Dacthal, the U.S. Environmental Protection Agency (EPA) has issued an emergency order immediately suspending all registrations of the pesticide. The action represents the first time in 40 years that EPA has issued an emergency order to stop the use of a pesticide, and “follows years of efforts to require the submission of long-overdue data” to support a risk assessment, according to the agency.  

Dacthal is a weed-killer that was previously approved for use in both agricultural and non-agricultural applications, mostly being used by industry for produce crops like broccoli, Brussels sprouts, cabbage, and onions. Scientific literature has demonstrated that exposure to Dacthal during pregnancy affects fetal thyroid hormone levels, which can lead to low birth weight, impeded brain development, decreased IQ, and impaired fine motor skills.

“DCPA is so dangerous that it needs to be removed from the market immediately,” said an EPA spokesperson. The emergency suspension was executed under the under the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA).

At the time of the emergency order’s issuance, Dacthal is undergoing registration review, a process for the regular reevaluation of registered agricultural chemicals to ensure they cause no unreasonable adverse effects on human health or the environment. In 2013, the agency issued a Data Call-In (DCI) to AMVAC Chemical Corporation, the sole manufacturer of Dacthal, requiring it to submit more than 20 studies to support the existing registrations of the herbicide, due by January 2016. The required data included a comprehensive study of the effects of Dacthal on thyroid development and function in adults, and in developing young before and after birth. Several of the studies that AMVAC submitted from 2013–2021 were considered insufficient to support the DCI, while studies about thyroid affects and other charges were not submitted at all.

In April 2022, EPA issued a notice of intent to suspend technical-grade DCPA product (used to manufacture end-use products) based on AMVAC’s failure to submit the complete set of required data for almost 10 years, including thyroid studies. While AMVAC submitted the required thyroid study in August 2022, EPA suspended the registration based on AMVAC’s continued failure to submit other outstanding data, following an administrative hearing.

In November 2023, the data submission suspension was lifted after AMVAC submitted sufficient data.

However, in May 2023, EPA released its assessment on the risks of occupational and residential exposure to products containing DCPA, following its analysis of the thyroid study submitted by AMVAC. The assessment found health risks associated with DCPA use and application, even when personal protective equipment and engineering controls are used. In a letter to AMVAC dated March 27, 2024, EPA restated the risks the agency found and noted that the agency would be pursuing regulatory options as soon as possible, which could include canceling the pesticide’s registration or seeking an emergency suspension.