A new campaign by the Green Party, calling for greater caution around Roundup and other glyphosate-based herbicides, is in its early days. However, early reactions to the campaign have already provided ample evidence of the messy interface between science, journalism and politics.

In January, the Greens launched a petition calling for an end to the use of glyphosate in public places such as parks and roadsides, and calling on the EPA to formally reassess the chemical's safety.

"We need to pull this stuff out of the streets and parks," said Green MP Steffan Browning. "More studies are needed."

Coinciding with the campaign launch, Browning and the Greens released a comprehensive report on health dangers linked to the popular weedkiller.

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Pundits were quick to jump to the defence of agriculture's favourite spray - it's the most-used herbicide in the world. In response to the Greens' campaign, the government-funded Science Media Centre released a primer prominently featuring the she'll-be-right perspective of Kerry Harrington, a Weed Science lecturer at Massey University. Harrington is not a toxicologist; in fact, his research is practical, focusing on using herbicides rather than on their side effects. However, journalists ignored this fact, and in the week following the Greens' campaign launch, he was New Zealand's most widely quoted scientist on glyphosate.

Harrington's comments inspired such headlines as the Manawatu Standard's "Glyphosate spraying risk the same as being a hairdresser." The implicit assumption: because one organisation, the International Agency for Research on Cancer (IARC), has identified both glyphosate use and hairdressing as "probable" cancer risks, the two activities carry the same risk level.

Much hinges on one ambiguous but carefully chosen word: "probable." Glyphosate became the focus of international scrutiny in March 2015, when, after a comprehensive review, the IARC's panel of international experts declared that glyphosate is "probably carcinogenic." In official terms, according to the IARC, "probably" means that according to the scientific literature, there is "limited evidence of carcinogenicity in humans and sufficient evidence of carcinogenicity in experimental animals."

However, though the IARC affirms that lab mice can get cancer from glyphosate, they make no claims as to what dose is safe for humans, and whether letting your kids play on a Roundup-sprayed playground is actually dangerous.

Nevertheless, in the year since the IARC report came out, the international reaction has been strong. The reaction has been swiftest in the EU. France has moved to stop selling glyphosate over the counter to the public; other countries are exploring similar actions; and a growing number of cities, most notably Barcelona and Edinburgh, have decided to stop using glyphosate sprays altogether.

However, the focus on the IARC report has also drawn attention away from a growing wider body of research on glyphosate's effects. The Greens' recent report compiles a long list of peer-reviewed scientific studies of health harms. Multiple studies from South America show damage to DNA in farmworkers and their children living near glyphosate-sprayed areas. In the lab, glyphosate has been found to damage human and animal DNA, affect the human endocrine system, and cause malformations of developing animal embryos.

The EPA won't yet comment on the Greens' report. But ultimately the future of New Zealand's go-to weedkiller will be in their hands.

For now, the agency is keeping quiet on whether they will in fact choose to reassess glyphosate - which would entail a long and detailed review of the science, and a public consultation.

"We would only review our existing glyphosate approvals if new information indicates that our risk management measures are inadequate," says Sarah Gardner, EPA General Manager of Applications and Assessments. "It is possible that new information may result in further work by the EPA to establish grounds for a chief executive initiated reassessment."

"It's on the chief executive's reassessment list - but when are they going to get to it?" asks Steffan Browning. "It needs to be done urgently and objectively."

EPA officials say they always take the full spectrum of scientific evidence into account. "The Environmental Protection Authority monitors international developments and the latest research available on glyphosate through a wide range of scientific media," Gardner says.

However, records of EPA's decision processes paint a more variable picture. For example, in 2009, ERMA (the EPA's predecessor) approved a glyphosate-based herbicide called GF-1280. According to the decision document, ERMA based its safety evaluations entirely on toxicity data supplied by the manufacturer, Dow AgroScience. Dow's data came from private lab animal studies that the company commissioned.

In subsequent years, EPA went on to use that 2009 approval as the basis for the approval of further glyphosate-based herbicides, according to an EPA staff member's correspondence with pesticide researcher Jodie Bruning of RITE (Requirement for Independent Toxicity Evaluations).

However, while herbicides are typically approved based on their active ingredients, lumping together all glyphosate sprays appears to neglect recent science. A 2012 study by French researchers at the University of Caen, published in the journal Toxicology, found that complete glyphosate herbicides - that is, glyphosate with cocktails of adjuvants added - vary in their toxicity to cells. In the lab, all nine herbicides tested were more toxic than the chemical glyphosate was on its own.