A public health expert wants Roundup for private use banned.

The EU's refusing to renew the licence of glyphosate, the key ingredient used in the weed killer.

Professor Jeroen Douwes from Massey University said it follows a report by the International Agency for Research on Cancer that's concluded it's probably a carcinogen to humans.

He said there are other weed killers people can use in their own gardens.

"I also believe that we should be looking at restrict [Roundup's] use in public places, possibly banning it there as well."

However, Environmental Protection Authority chief scientist Dr Jacqueline Rowarth believes the chemical in Roundup is about as cancer-causing as red meat or fried food.

The EPA class glyphosate is classed as a category 2A human carcinogen, along with red meat and frying.

Rowarth said the point is how we're using it.

"We use glyphosate under specific dilutions and regulations, we tell everybody to wash their hands afterwards. It's actually one of the safest chemicals in the world."

Rowarth says glyphosate passes straight through the human body if ingested.