Does the IARCs classification of glyphosate as a 2a carcinogen specify the level of exposure needed to be probably carcinogenic? That is, would even the residual traces of glyphosate that are found on produce be potentially carcinogenic?

Expert response from Aimee Hood

Regulatory Science Communications Lead, Bayer Crop Science

Tuesday, 01/12/2015 12:04

In March 2015, IARC concluded that glyphosate belongs in a 2A category as probably carcinogenic to humans, a category that includes professions such as barbers and fry cooks. IARC’s conclusion conflicts with the overwhelming consensus by regulatory bodies and science organizations around the world like the U.S. Environmental Protection Agency (EPA), which concluded that there is evidence of non-carcinogenicity. 

IARC did not specify a level of exposure needed to be carcinogenic; their assessments do not take that into consideration. The American Cancer Society has written: 

“Although the IARC and NTP publish qualitative judgments regarding the evidence for carcinogenicity, they do not provide quantitative estimates of the magnitude of risk resulting from a specified level of exposure. Quantitative risk assessment is a critically important and often mandatory next step for decision-making that is left primarily to regulatory agencies” (CA CANCER J CLIN 2009;59:343–351).  

That type of assessment is what regulatory bodies, like EPA, take years to do. Regulatory authorities around the world continually review the safety of glyphosate and have found no evidence of carcinogenicity.

Henry Miller, former FDA regulator, does a nice job explaining this in an article in Forbes:

“IARC bases its conclusion on potential hazard rather than the actual risk of harm. What does that mean to you and me? Well, we regularly participate in hazardous activities that have the potential to harm us–we use knives, drive cars, fly on airplanes and cross busy streets. However, the risk–the probability that we will actually be harmed– associated with each of these activities is low.

“The same applies to the IARC’s analysis of glyphosate. The data (and a selected set of data, at that) were reviewed to determine whether glyphosate is capable of causing cancer. As with common chemicals like sugar, salt and water, and foods like nutmeg and licorice, glyphosate at very high doses is capable of causing harm to humans. That’s what the IARC ‘2A’ designation—“probably carcinogenic to humans”–essentially means. But one of the seminal tenets of toxicology is that “the dose makes the poison,” and the reality is that glyphosate is not a human health risk even at levels of exposure that are more than 100 times higher than the human exposures that occur under conditions consistent with the product’s labeling.

“Thus, IARC publishes qualitative assessments, not quantitative assessments of risk. That is left to regulatory agencies.

“So, what have government regulators concluded? Glyphosate is currently undergoing a routine review of its registration in Europe, which is being conducted by the German Risk Agency (BfR). This re-registration evaluation has been in progress since 2012, and as of January 2015 the BfR concluded:

• “In conclusion of this re-evaluation process of the active substance glyphosate by BfR the available data do not show carcinogenic or mutagenic properties of glyphosate nor that glyphosate is toxic to fertility, reproduction or embryonal/fetal development in laboratory animals.”
• "In epidemiological studies in humans, there was no evidence of carcinogenicity and there were no effects on fertility, reproduction and development of neurotoxicity that might be attributed to glyphosate.”

“Regulatory agencies typically review more data and in much more depth than the IARC. For glyphosate, seven companies (Adama, Arysta Life Sciences, Cheminova, Excel, Monsanto, Nufarm and Syngenta) have submitted data from multiple types of studies, which are evaluated by the U.S. EPA, the German BfR and other global regulatory agencies. By studying high-exposure individuals such as pesticide applicators, carcinogens can be identified, so regulators also take into consideration studies like the United States’ Agricultural Health Study (AHS), a prospective study of cancer in licensed pesticide applicators and their spouses from Iowa and North Carolina. This study is a collaborative effort involving investigators from National Cancer Institute, the National Institute of Environmental Health Sciences, the EPA, and the National Institute for Occupational Safety and Health.

“The bottom line is that the BfR examined all the information that IARC saw and much more.

“New data are emerging constantly, and there have been recent new scientific reviews that would have been unavailable to BfR before they issued their sanguine opinion. So, could any of these new documents have led IARC to their less favorable conclusion? No–because these reviews further affirmed the safety of glyphosate and the absence of linkage between glyphosate and cancer risk.”

Another scientific review was recently completed by the European Food Safety Authority (EFSA).  Jose Tarazona, head of EFSA’s Pesticides Unit, said: “This has been an exhaustive process – a full assessment that has taken into account a wealth of new studies and data. By introducing an acute reference dose we are further tightening the way potential risks from glyphosate will be assessed in the future. Regarding carcinogenicity, it is unlikely that this substance is carcinogenic.”

My colleague, Donna Farmer, talks more about the safety of glyphosate in this video.

Additional resources can be found here:

• IARC's Classification of Glyphosate - What does it mean for you?
• Glyphosate as a Carcinogen, Explained
• What can we say about exposure to glyphosate?
• INFOGRAPHIC: Examples of International Agency for Research on Cancer (IARC) Carcinogenic Classifications 
• IARC Cancer Classification at Odds with Health and Safety Regulators Worldwide

Expert response from Aimee Hood

Regulatory Science Communications Lead, Bayer Crop Science

Tuesday, 01/12/2015 12:04

In March 2015, IARC concluded that glyphosate belongs in a 2A category as probably carcinogenic to humans, a category that includes professions such as barbers and fry cooks. IARC’s conclusion conflicts with the overwhelming consensus by regulatory bodies and science organizations around the world like the U.S. Environmental Protection Agency (EPA), which concluded that there is evidence of non-carcinogenicity. 

IARC did not specify a level of exposure needed to be carcinogenic; their assessments do not take that into consideration. The American Cancer Society has written: 

“Although the IARC and NTP publish qualitative judgments regarding the evidence for carcinogenicity, they do not provide quantitative estimates of the magnitude of risk resulting from a specified level of exposure. Quantitative risk assessment is a critically important and often mandatory next step for decision-making that is left primarily to regulatory agencies” (CA CANCER J CLIN 2009;59:343–351).  

That type of assessment is what regulatory bodies, like EPA, take years to do. Regulatory authorities around the world continually review the safety of glyphosate and have found no evidence of carcinogenicity.

Henry Miller, former FDA regulator, does a nice job explaining this in an article in Forbes:

“IARC bases its conclusion on potential hazard rather than the actual risk of harm. What does that mean to you and me? Well, we regularly participate in hazardous activities that have the potential to harm us–we use knives, drive cars, fly on airplanes and cross busy streets. However, the risk–the probability that we will actually be harmed– associated with each of these activities is low.

“The same applies to the IARC’s analysis of glyphosate. The data (and a selected set of data, at that) were reviewed to determine whether glyphosate is capable of causing cancer. As with common chemicals like sugar, salt and water, and foods like nutmeg and licorice, glyphosate at very high doses is capable of causing harm to humans. That’s what the IARC ‘2A’ designation—“probably carcinogenic to humans”–essentially means. But one of the seminal tenets of toxicology is that “the dose makes the poison,” and the reality is that glyphosate is not a human health risk even at levels of exposure that are more than 100 times higher than the human exposures that occur under conditions consistent with the product’s labeling.

“Thus, IARC publishes qualitative assessments, not quantitative assessments of risk. That is left to regulatory agencies.

“So, what have government regulators concluded? Glyphosate is currently undergoing a routine review of its registration in Europe, which is being conducted by the German Risk Agency (BfR). This re-registration evaluation has been in progress since 2012, and as of January 2015 the BfR concluded:

• “In conclusion of this re-evaluation process of the active substance glyphosate by BfR the available data do not show carcinogenic or mutagenic properties of glyphosate nor that glyphosate is toxic to fertility, reproduction or embryonal/fetal development in laboratory animals.”
• "In epidemiological studies in humans, there was no evidence of carcinogenicity and there were no effects on fertility, reproduction and development of neurotoxicity that might be attributed to glyphosate.”

“Regulatory agencies typically review more data and in much more depth than the IARC. For glyphosate, seven companies (Adama, Arysta Life Sciences, Cheminova, Excel, Monsanto, Nufarm and Syngenta) have submitted data from multiple types of studies, which are evaluated by the U.S. EPA, the German BfR and other global regulatory agencies. By studying high-exposure individuals such as pesticide applicators, carcinogens can be identified, so regulators also take into consideration studies like the United States’ Agricultural Health Study (AHS), a prospective study of cancer in licensed pesticide applicators and their spouses from Iowa and North Carolina. This study is a collaborative effort involving investigators from National Cancer Institute, the National Institute of Environmental Health Sciences, the EPA, and the National Institute for Occupational Safety and Health.

“The bottom line is that the BfR examined all the information that IARC saw and much more.

“New data are emerging constantly, and there have been recent new scientific reviews that would have been unavailable to BfR before they issued their sanguine opinion. So, could any of these new documents have led IARC to their less favorable conclusion? No–because these reviews further affirmed the safety of glyphosate and the absence of linkage between glyphosate and cancer risk.”

Another scientific review was recently completed by the European Food Safety Authority (EFSA).  Jose Tarazona, head of EFSA’s Pesticides Unit, said: “This has been an exhaustive process – a full assessment that has taken into account a wealth of new studies and data. By introducing an acute reference dose we are further tightening the way potential risks from glyphosate will be assessed in the future. Regarding carcinogenicity, it is unlikely that this substance is carcinogenic.”

My colleague, Donna Farmer, talks more about the safety of glyphosate in this video.

Additional resources can be found here:

• IARC's Classification of Glyphosate - What does it mean for you?
• Glyphosate as a Carcinogen, Explained
• What can we say about exposure to glyphosate?
• INFOGRAPHIC: Examples of International Agency for Research on Cancer (IARC) Carcinogenic Classifications 
• IARC Cancer Classification at Odds with Health and Safety Regulators Worldwide