City services minister Chris Steel said he remained concerned about the "potential health impacts" of glyphosate, the active chemical in the popular Roundup weed spray produced by Monsanto.

Canberra's city services directorate used about 6000 litres of glyphosate across the capital - including parks - per year, mainly to combat weeds like African love grass.

Mr Steel said other herbicides or the use of steam had been less effective or safe.

"The government is actively monitoring international and national developments in relation to human health and for environmental issues such as impact on bee populations," Mr Steel said.

The concerns have sprouted from successful lawsuits in the United States, where juries in three suits have found plantiffs' cancer to be caused by the chemical.

The lawsuits have cost Bayer, the parent company of Monsanto, billions of dollars.

The Australian Pesticides and Veterinary Medicines Authority, which approves the use of agricultural chemicals, currently advises glyphosate is safe to use if instructions on use are followed.

According to chemistry and pharmacology experts this is the right move but they said while cancer links are thin, there is still cause for concern.

Several Sydney local councils have ceased use of Roundup due to American court cases and the Victorian government is currently reviewing its use in the state.

A Melbourne gardener has recently launched legal action against Monsanto, claiming his cancer was caused by 18 years of exposure to glyphosate. Separately, personal injury firm Maurice Blackburn is considering a class action in Australia.

Australian National University emeritus professor and founding head of the now-pesticides authority, Ben Selinger, said concerns over the glypohsate and Roundup's cancer links were "not irrational".

"People shouldn't say 'Blah, blah, it's all bullshit' and people shouldn't say, 'Well, terror, terror, we're all going to get cancer'," Professor Selinger said.

"It's all a bit of common sense."

Professor Selinger said exposure to glyphosate should be kept to a minimum.

He said part of the anger against Monsanto, the creator of Roundup, was based off the company's notorious reputation.

"Monsanto is not a nice company," Professor Selinger said.

"Their scientists are good."

He pointed to the company's previous handling of its genetically modified "Roundup Ready" crop seeds; seeds designed by Monsanto to be resistant to Roundup.

Farmers were effectively forced to keep using the seed and when they treated their crops with Roundup, neighbouring farmers lost crops.

Professor Selinger said despite so many people using glyphosate for so long, the cancer links were still thin.

When asked about trace elements sometimes appearing in food, Professor Selinger said this could happen if crops were picked too quickly after being treated with Roundup.

Last month, a US court awarded a Californian couple $A2.9 billion after a jury found Roundup had caused their non-Hodgkin's lymphoma. In September, a Californian jury awarded $A389 million to a gardener, finding his terminal cancer had been caused by Roundup.

He said in this latter case, it appeared as if the plaintiff had been excessively exposed to glyphosate.

"You've got twelve average blokes or sheilas ... they come out and go, 'This poor bastard suffered'," Proessor Selinger said.

"I don't know how you can have such a non-professional way of awarding challenges."

University of Adelaide pharmacologist Dr Ian Musgrave said the Environmental Protection Authority in the United States' advice on glyphosate was it was not carcinogenic to humans.

This was repeated by the Australian pesticides authority, the World Health Organisation and the European counterpart.

"Court cases don't decide science and quite often results of court cases might fly int he face of our best evidence," Dr Musgrave said.

He said 20 year study of 55,000 people found no association with glyphosate and cancer.

"You can never be 100 per cent certain of anything, of any chemical," Dr Musgrave said.

"You should always treat agricultural chemicals with respect."

"There's a lot of emotion around this."

Dr Musgrave warned that alternatives to Roundup and sprays containing glyphosate could be even more risky considering the lack of studies.

"They should be very careful what they wish for," Dr Musgrave said.

Despite the pesticides authority's belief in the relative safety of the product, Dr Musgrave said the issue wasn't going to go away.