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The world’s most used weed-killer is probably carcinogenic – so what?

By Meg Sears, and the PCN writers’ circle

The world’s (and Canada’s) most used herbicide, glyphosate, was recently classified as a probable cause of cancer by the International Agency for Research on Cancer (IARC). Within the World Health Organization (WHO), IARC’s chief goal is to identify causes of cancer.

Right on cue, Health Canada’s Pest Management Regulatory Agency (PMRA) announced its long-planned re-evaluation of glyphosate, noting:

“The World Health Organization’s (WHO) International Agency for Research on Cancer (IARC) recently assigned a hazard classification for glyphosate as “probably carcinogenic to humans”. It is important to note that a hazard classification is not a health risk assessment. The level of human exposure, which determines the actual risk, was not taken into account by WHO (IARC). Pesticides are registered for use in Canada only if the level of exposure to Canadians does not cause any harmful effects, including cancer.” (emphasis added)

Hang on. IARC used Canadian data – Canadians getting cancer related to our use of glyphosate – so how can it be true that Canadian human exposure was not taken into account? Population-based studies are expensive and can easily miss real effects, so research focuses on workers with clearer job-based exposures. It does not follow, however, that results only apply to workers. Many people are more vulnerable than workers (e.g. the very young and those with compromised health). Exposure can occur via food, water, as well as air in proximity to conventional agriculture, and urban uses (where exposure can be high due to misuse, drift, unscheduled applications by many neighbours, and lack of protective gear).

The only way to avoid glyphosate is to choose organic foods and to practice organic agriculture and alternative/organic landscape management.

Glyphosate – a small molecule with potent effects

Glyphosate kills plants by inhibiting an essential enzyme. It was originally concluded that glyphosate is “safe” for people because human cells do not use this enzyme. This enzyme is essential in bacteria, however, so glyphosate is also an antibiotic. What might this mean …

  1. for people? There are more bacterial cells than human cells in our bodies, particularly in the gut. We rely upon these bacteria (the microbiome) to digest food, and to produce vitamins and other chemicals essential for health even beyond the gut. The microbiome affects the health of the whole body, including the immune and neurological systems, as well as cancer incidence. Shifts in microbial populations with chronic glyphosate exposure have resulted in increases in pathogenic and decreases in beneficial microbes in chicken microbiota (in vitro) and in cow’s rumen. For humans, such effects have been characterized as a pathway to modern diseases.
  2. for the earth? Glyphosate similarly affects populations of micro-organisms in the soil. As beneficial bacteria are killed, fungal pathogens may increase. This can affect food quality, with increased levels of, for example, Fusarium. This carcinogenic fungus contaminates food. Notably, farmers transitioning to organic agricultural methods experience decreases in the level of Fusarium.
  3. for foods? Glyphosate is sprayed on grains pre-harvest, to kill the plant and hasten drying down. This process is intended to lower contaminants such as Fusarium. As noted above, it is hard to know if Fusarium would be such a problem if the microbial community had been left undisturbed to do its work. Canadian limits on glyphosate in grains now accommodate this practice.
  4. for antibiotic resistance? Concerns are mounting that glyphosate and other common weedkillers may contribute to development of antibiotic resistant “superbugs” in agriculture and hence in us.

Glyphosate is also a chelator (from Greek for “claw”) that wraps around toxic metals such cadmium or lead, and mobilizes them so they may be more readily taken up by plants. Cadmium in wheat and pulses (e.g. peas) may exceed international standards. (Canada has no standard.) Cadmium is present in Canadian fields because areas of the prairies have naturally high levels of cadmium, as does Canadian potash used for fertilizer. Food crops like grains and brassicas (cabbage, broccoli, etc.) naturally accumulate cadmium. A recent review of organic versus “conventional” foods highlighted recent reports of more cadmium in foods produced “conventionally” – with herbicides such as glyphosate. We don’t need more cadmium.

Spray glyphosate, and what happens to the people?

Glyphosate has been used in “drug wars,” to kill coca and poppies in Colombia. Next door in Ecuador, César Paz-y-Miño’s university-based researchers found DNA damage correlated with how close people were to sprayed areas. Analyses using a less sensitive test, financed by the US and Colombia governments, did not replicate these findings. Nevertheless, with the recent IARC finding, and in light of long-standing health concerns in the areas, Colombia’s president declared that the coca will no longer be sprayed with glyphosate. There is even speculation that ending the spraying of populations and their crops, including their food, may open the door for talks between the government and rebels.

Argentina’s agricultural revolution has been based on genetically modified organisms (GMOs) that tolerate glyphosate, GM soy in particular, accompanied by copious applications of the weedkiller. Dramatic increases in cancers, spontaneous abortions, birth defects as well as skin, respiratory and neurological conditions in farming regions led the federation of health professionals, the 27000 member FESPROSA to call for a ban on glyphosate in April 2015 (an English explanation is here).

Severe kidney disease is also being linked with glyphosate and water hardness, possibly related to mobilization of toxic metals like cadmium and arsenic that are extremely toxic to the kidney. Cadmium and arsenic are also carcinogens, so higher rates of cancers might be expected among those who do not succumb to kidney failure. Cadmium and arsenic are higher in Sri Lankans living in areas where chronic kidney disease is endemic. Cadmium and arsenic are also carcinogens, so increased cancers are possible among those who do not succumb to kidney failure. Thousands of citizens, including farm workers in Sri Lanka, as well as South America, suffering chronic kidney disease and kidney failure are blaming agricultural chemicals, and governments are responding with restrictions on glyphosate. Dehydration under poor working conditions probably also contributes to the condition in workers.

Animal studies

Sometimes we will not see cancer in animals with exposure to an agent that causes cancer in humans, but it is rarer for an agent to cause cancer in animals and not pose risks to humans. As well as human data of cancer in workers, IARC highlighted an older US mouse study. The US Environmental Protection Agency had initially given it weight back in the 1970s, but had then been persuaded otherwise. The study was re-re-evaluated by IARC. According to US Environmental Health expert Dr. Devra Davis (personal communication, May 2015):

In the case of glyphosate and cancer, one important animal study stands out. That study used a type of mouse bred never to get the disease. Four animals exposed to glyphosate developed the same very rare cancer in a single study. Not a single case of cancer was expected. The chances of that happening are close to one in a billion.

More recently, Professor Séralini and his group in France found increased tumours and organ damage in a long-term (2 year) animal feeding study of GMO corn and/or Roundup (glyphosate – active ingredient), published in Food and Chemical Toxicology. Amidst considerable consternation, a previous Monsanto employee then joined the journal editorial board. The study was subsequently retracted, for the unusual reason that the results were inconclusive. (Science is a process of building upon others’ results and is seldom conclusive; moreover, efforts are made to encourage publication of equivocal and negative studies, to reduce bias in the body of literature). Ultimately the landmark study was re-published along with all the data, as well as a call for responsibility and industry data, and a history of interference in this topic.

But glyphosate is safe?! (we are repeatedly told)

The majority of glyphosate is used along with seeds that are genetically engineered to withstand high doses that kill all other plants. In response to a pervasive mantra that genetically modified organisms (GMOs) and glyphosate are “safe,” in 2015 over 300 scientists and physicians signed on to a peer-reviewed, published analysis of how there is no consensus regarding genetically modified foods or related crop inputs.

A failing, futile strategy – the pests are getting stronger.

An original selling point for glyphosate-tolerant GMOs was that glyphosate could replace phenoxy herbicides (e.g. 2,4-D) for use on cereals such as corn. Glyphosate was presumed to be relatively non-toxic, while phenoxy herbicides had gained notoriety for dioxin contamination (typified by Agent Orange), and association with various harms including cancer. Glyphosate use surged with genetically modified crops, because Roundup can be sprayed on fields planted with GM “Roundup Ready” seeds, and everything else will be killed. At least that was the plan. Things did not go as planned. Weed resistance was the result, which has led to a chemical arms race, with seeds resistant to multiple herbicides and combination products increasingly being promoted, while farmers have been left with very vigorous weeds.

Act now, rather than waiting for yet more harm

The World Health Organization’s IARC has said that glyphosate probably causes cancer. Health Canada is proposing minor label changes but the herbicide would still be available for sale and wide-scale use.

We know that glyphosate has multiple harmful effects, and it is in urine, blood and even breast milk. Should we wait for more harm, as we did with lead, asbestos, tobacco, and many other carcinogens, or should we start today to minimize exposures?

Too often we hear that there is no evidence of harm from pesticides, not because we have proof of safety, but because we have not collected data. Moving ahead with our eyes wide open involves routinely collecting and making publicly available information such as pesticides sales and use, environmental data (e.g. air, water, food contamination), adverse effects and detailed population health data, so that we can learn from the past. While we’re at it, let’s build a present and future that we will not regret.

GMO Inquiry: To learn more about GMOs, Canadian agriculture and glyphosate use, check out the Canadian Biotechnology Action Network’s GMO Inquiry 2015.