EFSA executive director Bernhard Url has written to a group of 96 senior scientists rejecting their criticisms in an ongoing row about the safety of glyphosate.
In November, EFSA issued an opinion that glyphosate is unlikely to cause cancer, which contradicted the findings of the International Agency for Research on Cancer (IARC), part of the World Health Organization, which said in March that glyphosate is "probably carcinogenic to humans".
EFSA's conclusion could lead the 28-member European Union to renew approval for glyphosate, which was brought into use by Monsanto in the 1970s and is used in its top-selling product Roundup as well as in many other herbicides around the world.
US-based Environment Defense Fund representative Portier said in the joint letter: "We urge you and the European Commission to disregard the flawed EFSA finding on glyphosate in your formulation of glyphosate health and environmental policy for Europe."
It called for "a transparent, open and credible review of the scientific literature".
EFSA executive director Bernhard Url replied: "I strongly disagree with your contention that EFSA has not applied open and objective criteria to its assessment.
"We should not compare this first screening assessment with the more comprehensive hazard assessment done by authorities such as EFSA, which are designed to support the regulatory process for pesticides in close cooperation with member states in the EU," Url added.
The two groups are set to meet in February.
Monsanto said: "Monsanto is confident in the clear scientific consensus about the safety of glyphosate, in agreement with the findings of EFSA’s comprehensive review published in November 2015.
"IARC’s March 2015 opinion is an outlier in this body of scientific evidence. However, IARC’s opinion fits with anti-chemical campaigners views and marketing needs; we expect these groups to continue to invest in communications seeking to cast doubt on the scientific consensus about glyphosate safety, especially during 2016 as the EU glyphosate re-registration process continues.
"The reason IARC and EFSA can come to different conclusions about glyphosate safety is because their approach and assessment methods are different, see: http://www.monsanto.com/iarc-roundup/pages/default.aspx"
"Other expert views on the contrast between IARC and EFSA are here: http://www.sciencemediacentre.org/expert-reaction-to-efsas-conclusions-on-glyphosate-safety/"
"Which conclusion or opinion is ‘correct’ depends on your point of view on the methods used by the two agencies. For me, the EFSAmethodology is the one that is more scientific, pragmatic and balanced."
"Specifically responding The Guardian article, it’s important to note that in drawing their conclusions EFSA did not "disregard" IARC’s opinion. EFSA make clear they considered what IARC published in their letter published here: http://www.efsa.europa.eu/sites/default/files/EFSA_response_Prof_Portier.pdf"