The Environmental Protection Authority has issued an urgent alert for people to stop using weedkiller because of significant concerns about its effects on unborn children.

The EPA began investigating Dacthal or DCPA herbicides last week after they were pulled off shelves in the United States.

It is now urging people to avoid the herbicide, which is used to control annual grasses and broadleaf weeds in vegetable growing globally.

"We urge anyone currently using a product containing chlorthal-dimethyl to stop and to consider alternatives.

"If people can't avoid using these products, the EPA advises they take all precautions to avoid exposure for people who are pregnant or could be pregnant."

This includes restricting access to sprayed areas and making sure nobody else is around during spraying Presow said.

The US Environmental Protection Agency found a risk of thyroid hormone changes in the unborn children of pregnant bystanders, women who apply chlorthal-dimethyl, or those who enter treated fields after the substance has been applied.

These changes can cause low birth weight and irreversible and lifelong impacts, such as impaired brain development and motor skills.

Presow said the EPA had set up a working group to look at how this herbicide is being used here, and to take rapid action to ensure it continued protecting people's health and safety.

"While this is happening, we have put out a red alert to ensure the public is aware of the potential risks."

Horticulture New Zealand said Dacthal was outdated and the vast majority of growers preferred to use newer herbicides.

This story was originally published by RNZ