"Paraquat is a highly toxic substance and so we'd be very concerned about its continuing use in the EU," said Sandra Bell, pesticides adviser to environmental group Friends of the Earth.

"Any allowance of its use across the European Union would be a backwards step," she told Reuters.

Environmentalists have long campaigned for the complete removal from EU markets of paraquat, one of the very few herbicides that are acutely toxic.

Paraquat became widely known when it was sprayed on Latin American marijuana fields in the 1970s as a defoliant and it is currently authorised as a weedkiller in 10 EU member states.

But Sweden, Finland, Denmark and Austria have banned the chemical for many years, while Germany has restrictions on it.

"Certain countries decided that they just don't want it used in their country. If they're able to manage weeds without it, it begs the question of why other countries need to use it," said Stephanie Williamson at the UK-based Pesticide Action Network.

Critics say it is impossible to handle paraquat safely and claim that the chemical harms the lungs, skin and eyes of workers handling it. Paraquat producers deny these charges.

A fast-acting non-selective herbicide used to kill weeds, paraquat destroys green plant tissue on contact. If this month's proposal is agreed, it could be sold throughout the EU, subject to strict legislative controls from Brussels.

In 2001, EU scientists classed paraquat as toxic but not a major risk to operators or soil-dwelling organisms. There was a small risk for ground-breeding birds and animals such as hares.

If the EU experts include paraquat as an authorised product, its use would remain highly restricted and it would most likely not be sold to the public, a Commission official said.

To highlight its toxicity, extra chemicals could be used to give it a particularly bad smell or cause immediate vomiting if accidentally consumed, he added.