A Chemist in Langley

Understanding the difference between a “hazard” and a “risk” or why scare stories about glyphosate and pesticides in your food shouldn’t frighten you

I have written a lot at this blog about how chemical risks are communicated to the public and so I am often asked about news stories depicting the latest science scare story. Sometimes they are handled badly, like the CTV National news report about glyphosate with the chilling title: Weed-killing chemical found in pasta, cereal and cookies sold in Canada: study. Sometimes it is done much better, like the Global New take on a similar topic with ‘Dirty Dozen’: Do these fruits and veggies really have harmful amounts of pesticide? As I will explain in this blog post, ultimately it comes down to understanding that we have to stop asking the question “can this compound cause cancer?” and instead ask: “is this compound expected to cause cancer at the concentrations encountered in that study?” because while the answer to that first question may be “yes”, the answer to the second will almost always be “no”. In asking those questions we can understand the fundamental difference between a hazard and a risk.

As many of my readers know, one of my areas of professional practice is risk assessment. In my practice I often hear people interchange the words “hazard” and “risk“. These are not interchangeable terms. I can’t repeat this enough, the words “hazard” and “risk” mean very different things and it is important to understand that something can be a hazard without posing a serious risk.

Notice the difference? An unfenced swimming pool is a hazard to toddlers. But if that unfenced swimming pool is on a fenced estate where toddlers are not allowed then it poses no risk to your toddler.

So let’s bring this back to the idea of pesticides like glyphosate.

Well by now we all know that the International Agency for Research on Cancer (IARC) has designated glyphosate as a Group 2A carcinogen meaning they believe it is “probably carcinogenic to humans”.

There are very strong arguments that the IARC conclusion was incorrect and that glyphosate is likely not a carcinogen . The UN Food and Agriculture Organization and World Health Organization, the European Food Safety Authority (EFSA), Health Canada and the US EPA all agree on that the IARC is wrong. Strong articles have even been written to suggest the IARC decision was fundamentally flawed.

That being said, let’s assume that every other major health agency is wrong and the IARC is right. In their Monographs (research studies) the IARC makes a very important point

The IARC Monographs Programme evaluates cancer hazards but not the risks associated with exposure. The distinction between hazard and risk is important. An agent is considered a cancer hazard if it is capable of causing cancer under some circumstances. Risk measures the probability that cancer will occur, taking into account the level of exposure to the agent. The Monographs Programme may identify cancer hazards even when risks are very low with known patterns of use or exposure [my bold].

Even in their own document the IARC explains that a pesticide can pose a hazard and not be a risk to human health.

The other thing to understand is analytical chemists are really, really good at finding very small amounts of compounds in mixtures. As I pointed out in a previous post; analytical chemistry has got so precise that a modern mass spectrometer can distinguish to the parts per trillion range. That would be 1 second in 30,000 years. So when an activist says they found “detectable” concentrations of a pesticide in a sample you should probably take that with a grain of salt. Reading the two studies presented at the top of this blog they found pesticides in the parts per billion range. A part per billion would be a drop of water in an Olympic-sized swimming pool.

In toxicology and risk assessment the way we determine whether an exposure to a chemical poses a risk is to calculate the reference dose, (RfD). A RfD is a concentration or dose of a compound in question to which a receptor may be exposed without causing adverse health effects (i.e. a dose that is considered “safe” or “acceptable”). For pesticides, Health Canada calculates maximum residue limits (MRL) that represent concentrations of a compound that are not considered to pose a significant risk to the public.

Health Canada has established MRLs for glyphosate for all sorts of foodstuffs. The entire list is here. This list establishes concentrations that are considered to be entirely safe (i.e pose no significant threat to the public). This is where journalists like in the CTV story, can get it wrong. To explain let’s look at a post from Joe Schwarcz who looked more deeply into that study:

the highest amount of glyphosate found was 760 ppb which is way, way below Health Canada’s standard for oat products at 15,000 ppb. A small child eating 100 grams of the cereal would consume 0.076 milligrams of glyphosate. Most regulatory agencies have concluded that consumption up to 0.5 mg/kg body weight per day presents no problem, so that a 10 kg child could consume 5 mg per day. The 0.076 mg consumed is 1/66th of this.

That is, a 10 kg child (a baby) would have to eat 66 bowls of Cheerios a day to experience a detectable risk to their health.

This brings us back to our story about fear-mongering and glyphosate. I can’t count the number of people on my social media feed who pointed out that a jury found Monsato guilty for causing a man’s cancer. Well I am not the first person, nor will I be the last, to point out that US juries are not known for their ability to understand science. Another jury once believed the story about an infamous glove “if it doesn’t fit, you must acquit” and we now all agree they were out to lunch.

Instead of trusting US juries for our science I think we should stick with the professionals and they all agree (even the IARC) that the concentrations of glyphosate you encounter in your daily life in your breakfast cereals and in your nutritious fruits and vegetables are not high enough to cause any harm. In other words, while glyphosate may represent a theoretical hazard to human health it does not pose a real risk to you or your children.

To conclude let me reiterate. When you see a study like those presented above do not ask: “can this compound cause cancer?“. Instead ask: “is this compound expected to cause cancer at the concentrations encountered in that study?” By doing so you will get the correct answer. Then you can ignore the fear mongers and go back to eating those healthy fruits and vegetables in peace.

Image from Shutterstock

Author’s note:

Because I deal with risk all the time in this blog I have prepared a series of posts to help explain the risk assessment process. The posts start with “Risk Assessment Methodologies Part 1: Understanding de minimis risk” which explains how the science of risk assessment establishes whether a compound is “toxic” and explains the importance of understanding dose/response relationships. It explains the concept of a de minims risk. That is a risk that is negligible and too small to be of societal concern (ref). The series continues with “Risk Assessment Methodologies Part 2: Understanding “Acceptable” Risk” which, as the title suggests, explains how to determine whether a risk is “acceptable”. I then go on to cover how a risk assessment is actually carried out in “Risk Assessment Methodologies Part 3: the Risk Assessment Process. I finish off the series by pointing out the danger of relying on anecdotes in a post titled: Risk Assessment Epilogue: Have a bad case of Anecdotes? Better call an Epidemiologist.