Welcome to “chemicals and society”, where we highlight the current understanding of the biological effects and safety of some of the most common chemicals in today’s society.

Today’s Chemical: Glyphosate

What is glyphosate? Glyphosate is the active ingredient in Roundup, a herbicide which happens to be one of the most widely used in the world. There are several reasons why Roundup is so popular. It’s a very good herbicide, killing actively growing plants quickly with a single application. It also is relatively safe, because it targets an enzyme that plants have but animals do not (5-enolpyruvylshikimate-3-phosphate synthase, say that ten times fast!), and it doesn’t accumulate in the environment like many earlier generation herbicides. Another reason it’s popular is that many GMO crops are engineered to resists it’s effects, rendering it an ideal herbicide for control of weeds when growing these crops.

Glyphosate and Cancer. If you have heard of glyphosate recently, it probably because of reports that it causes cancer. So let’s start with this. Here’s the story:

When it was first approved for use, the data suggested that glyphosate posed no carcinogenic (cancer-causing) risk. As is always the case, scientists kept an eye on the data as the use of this chemical increased dramatically over the years. Some data seemed to indicate some cancer risk, while most did not. Health authorities in the United States, Japan, Canada, most of Europe, and many other countries do not consider glyphosate to be linked to cancer.

The controversy started when a group called the International Agency for Research on Cancer (IARC, which is part of the World Health Organization, WHO) classified glyphosate as a “probable human carcinogen” in 2015. This shocked a lot of people, because we use a lot of this stuff, and we had been told it was safe. In response to this, the European Union (EU) performed an assessment of their own and disagreed – classifying it as “unlikely to be a human carcinogen”. WHO then joined forces with the Food and Agriculture Organization (FAO) of the United Nations and sided with the EU (not a carcinogen). Things got even more complicated when it was alleged that sections of the EU report were copied word for word from some of early reports by Monsanto, the initial manufacturer of the pesticide. The authors of the report have of course denied that there was any plagiarism involved. Basically, this whole thing has turned into the science equivalent school yard brawl, but despite the back and forth, the EU recently renewed the license for use of glyphosate for another 5 years.

To date, the IARC is the only scientific body that has classified glyphosate as a carcinogen. You may have heard about a legal battle in California over this – this is because California’s Proposition 65 requires that everything in the state containing a potentially cancer-causing chemical to be labeled as such. Taking a cue form IARC, California proposed to label glyphosate-containing products as carcinogenic and this has resulted in law suits and even more bickering. Science fight!!!

So how did this happen? How can two scientific groups disagree over something like this. Well, that’s… complicated. It turns out that IARC didn’t look at all of the data, disqualifying some reports and not having access to others. This was likely a factor. IARC also has a bit of a reputation of classifying things with limited data – red meat and beverages over 65 °C (149 °F) are also listed as probable human carcinogens, which honestly makes no sense. However, the biggest reason for the different opinions is this: the IARC process is a hazard assessment, while the others (including all the local health authorities) is a risk assessment. What’s the difference? Glad you asked:

Hazard identification is the process by which you identify potential risks. This is the first step in a risk assessment. In occupational safety terms, a large vat of boiling hot acid hanging from the ceiling of an office is a hazard. In cancer risk assessment, you first need to figure out if a chemical can cause cancer before assessing the risk.

Risk assessment takes the hazard and considers the dose-response relationship of the effect in question as well as the exposure of actual people to the effect. In the case of the boiling hot acid, a risk assessment would consider how much of that acid would cause injury to a worker, and also how likely it would be that a worker would be exposed to the acid (is it in an unoccupied room, or hanging over someone’s desk?). In a cancer risk assessment, the dose of the chemical that could cause cancer needs to be taken into account along with how much of the chemical a typical person could be exposed to.

So, IARC believes that glyphosate can cause cancer. Many disagree with this, and a recent study found no increased risk in workers exposed to glyphosate. In reality, however, whether or not it can cause cancer is not important to the majority of the human population – those of us not involved in large scale manufacturing or application of the pesticide are exposed mainly through oral exposure (from residual levels on food) or when we spray the Roundup we bought at the hardware store in our own yards. For us, the question is will it cause cancer, and the answer to this question is that it is very unlikely to cause cancer. In all the animal studies showing potential carcinogenic effects, the doses used were many, many times higher than what most people are actually exposed to.

This conclusion may not feel satisfying. Why would we want a potentially cancer-causing chemical on our foods and in our gardens? The truth is that this is the world we live in already. While there is some debate about whether or not glyphosate can cause cancer, we are absolutely, 100% certain that cigarette smoke, alcohol, smoked or grilled foods, and the suns ray’s cause cancer. You are exposed to these every day, and whether or not you like it, the same is true for glyphosate – unless you eat an entirely organic diet, you are consuming very low quantities of it every day. This won’t give you cancer – even the folks at IARC would agree with this.

Now, that’s not to say we should be spraying glyphosate around indiscriminately. It likely reduces biodiversity of plants (since it kills most plants) as well at the insects that rely on some plants for food.  It’s not good for fish or snails either. And while it doesn’t accumulate in the environment, it hangs around longer then we’d like – showing up in soil, food, and people’s urine at low levels long after it’s use. Everything is toxic if you are exposed to enough of it, and while glyphosate is relatively non-toxic for a pesticide, it should still be handled with care. Don’t spray it all over yourself or anyone else, and of course don’t drink it.

So What’s the bottom line? People are freaking out about glyphosate. You’ll hear people saying that it is “toxic”*, that it’s poisoning our children, that it’s in our vaccines, and that it’s an attempt by Monsanto to kill us all (it’s off patent now, so Monsanto is not the only manufacturer). These statements do not match the facts. Even with respect to the potential to cause cancer, the jury is still out, and the large majority of experts do not believe there is a cancer risk to humans.  If glyphosate is going to cause you any harm at all, you’ll need a high dose, and that only comes from handling the concentrated pesticide yourself. Handle it with caution. Wear gloves, and a mask if you are spraying over your head or on a windy day. Don’t spray it on yourself or others, keep pets and children away from areas where you have sprayed until it has completely dried, and don’t let those pets or kids play in the dirt in areas where you regularly spray. If it really worries you, just don’t use it at all! This is common sense with any pesticide, and these basic safety precautions should eliminate any potential harm of this very common chemical.

* As a general rule, if anyone dismisses something as “toxic,” they likely have no idea what they are talking about. Since everything is toxic if you are exposed to enough of it, this word means nothing without context. Will a single drop kill you? Will bathing in it every day eventually give you cancer? When someone uses this term, press for more details, and if they don’t have them, find a better source for your information.