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Glyphosate 'Probably Carcinogenic to Humans' Latest WHO Assessment

glyphosate probably carcinogenic to humans

World authority experts selected free from conflict of interest

The world authority on cancer, the International Agency for Research on Cancer (IARC) of the World Health Organization (WHO) declared the herbicide glyphosate ‘probably carcinogenic to humans’ in its latest expert assessment [1, 2]. A Working Group of 17 experts from 11 countries met at IARC headquarters 3-10 March 2015 in Lyon, France. The meeting followed almost a year of review and preparation, including a comprehensive review of the latest available scientific evidence. The experts were selected on the basis of their expertise and most importantly, the absence of real or apparent conflicts of interest. The Working Group considered “reports that have been published or accepted for publication in the openly available scientific literature” as well as “data from governmental reports that are publicly available”. They evaluated five organophosphate insecticides and herbicides including glyphosate. The results, announced 20 March were as follows. The herbicide glyphosate and the insecticides malathion and diazinon were classified as probably carcinogenic to humans (Group 2A). The insecticides tetrachlorvinphos and parathion were classified as possibly carcinogenic to humans (Group 2B).

Significance of the assessment

To understand the real significance of the new assessment, some background information is needed. Substances and exposures that can lead to cancer are called carcinogens.

The IARC is part of the WHO, its major goal is to identify causes of cancer, and its classification for carcinogens is the most widely used and accepted in the world [3]. In the past 30 years, the IARC has evaluated the cancer-causing potential of more than 900 likely candidates, placing them into the following categories:

    Group 1: Carcinogenic to humans
    Group 2A: Probably carcinogenic to humans
    Group 2B: Possibly carcinogenic to humans
    Group 3: Unclassifiable as to carcinogenicity in humans
    Group 4: Probably not carcinogenic to humans

Commenting on the classification system, the American Cancer Society stated [3]: “Perhaps not surprisingly, based on how hard it can be to test these candidate carcinogen, most are listed as being of probable, possible, or unknown risk. Only a little over 100 are classified as “carcinogenic to humans.””

The Environmental Protection Agency uses a rating system similar to that of IARC [3]:

    Group A: Carcinogenic to humans
    Group B: Likely to be carcinogenic to humans
    Group C: Suggestive evidence of carcinogenic potential
    Group D: Inadequate information to assess carcinogenic potential
    Group E: Not likely to be carcinogenic humans

Thus, a classification of 2A in cancer-causing potential for glyphosate on the IARC is almost the highest possible categorization.

As stated in the IARC press release [1]: “Group 2A means that the agent is probably carcinogenic to humans. This category is used when there is limited evidence of carcinogenicity in humans and sufficient evidence of carcinogenicity in experimental animals.”

It should also be noted that the two insecticides placed in the lower category (2B) in terms of cancer-causing potential are both in restricted use.  Tetrachlorvinphos is banned in the European Union, but continues to be used in the US; while parathion has been severely restricted since the 1980s, and all authorized uses were cancelled in the European Union and USA by 2003.

Of the organophosphates in Group 2 A, diazinon has been used in agriculture and home and garden insect-control. It has been in low production especially after 2006 due to restrictions in the USA and the EU. Malathion is used in agriculture, public health and residential insect control, and continues to be produced in substantial volumes throughout the world. But it is minor league compared with glyphosate. As highlighted in the assessment [1, 2], glyphosate has the highest global production volume of all herbicides. The agricultural use of glyphosate has increased sharply since the introduction of genetically modified (GM) crops tolerant to glyphosate. The largest use worldwide is in agriculture, but it is also deployed in forestry, urban, and home applications in more than 750 different commercial products. Consequently, glyphosate has been detected in the air during spraying, in water, and in food. The general population is exposed primarily through residence near sprayed areas, home use, and diet.