Will using weedkiller give me cancer?


  • Wellness
  • Thursday, 25 Apr 2019

A farmer spraying his crop of grapes with weedkiller. — AFP

I have been reading about some litigation cases recently in the United States about some herbicides allegedly causing a man to have cancer. Now I want to know the truth, rather than Facebook rumours, so what exactly is a herbicide?

A herbicide is a chemical compound that is used to kill unwanted plants like weeds.

This is particularly important when you are a farmer with acres and acres of crops – weeds can destroy up to 40% of your crops.

And these are not your garden variety weeds either – you cannot pluck out these types of weeds by hand. If you have miles and miles of crops, like paddy fields and vegetable fields, you need something more to control pests and weeds.

Herbicides are not only used by farmers. They are used in what we call total vegetation control (TVC) programmes to maintain highways and railroads.

They are also used in forests and natural habitats for wildlife.

How do herbicides work?

Some herbicides kill certain unwanted plants while leaving the crops unharmed. Some act by interfering with the growth of just the weed by affecting the weeds’ hormones.

Others will kill all plant materials they come in contact with. These are called non-selective herbicides.

Think of them with the analogy of antibiotics. There are broad-spectrum antibiotics that kill most types of microbes they come in contact with. Then there are selective antibiotics that only target a certain type of microbe.

Are herbicides dangerous to a human being?

Overwhelming scientific evidence available points that they are not dangerous to humans.

Let’s talk about the widely-discussed glyphosate-based herbicides as an example.

Glyphosate is the active ingredient in many herbicides. It is a broad-spectrum systemic herbicide and crop desiccant. It works by inhibiting key plant enzymes.

It is effective in killing weeds, especially the common yearly broadleaf weeds and grasses that damage crops.

Glyphosate was discovered in 1970. It is very effective because it is absorbed through foliage (leaves) and not as much through a plant’s roots. It is most effective on plants that are actively growing.

Crops have been genetically engineered (GMO) to be resistant to glyphosate.

So, what does the scientific data on glyphosate say?

The truth is that glyphosate has been monitored by many bodies and governmental agencies for years, such as the US Environmental Protection Agency (EPA) and the European Food Safety Authority (EFSA), and even the US National Cancer Institute in a 2018 study following 50,000 pesticide applicators.

So, many regulatory bodies in countries as diverse as the United Kingdom, South Korea, Japan, Europe, Canada and Australia have all come to the same conclusion.

And that is that glyphosate is unlikely to pose a cancer risk to humans when used as prescribed.

And farmers certainly know how to use products as prescribed, just as you know how to mix the right amount of detergent into your laundry and a doctor knows how to prescribe the right dose of medicine for a patient.

This is a scientifically-proven dosage, which is not too low lest it be ineffective, and not too high lest it causes too many side effects.

Most scientific evidence finds no correlation of glyphosate to cancer, no matter what the rumours on Facebook say or what a jury verdict decides.

Juries are made out of people like you and me. And they do not necessarily go by scientific evidence, and have been known to be hugely swayed by emotion or how articulate the plantiff’s lawyer can be. (Remember the OJ Simpson case?)

There is only one study by the International Agency for Research on Cancer (IARC) that says glyphosate may be probably carcinogenic, but its risk is no greater than eating red meat.

The jury in the case where a man blamed a glyphosate-based herbicide for his cancer, based their verdict on that one conclusion.

So, the cancer risk of being exposed to a herbicide is equivalent to the cancer risk of eating red meat?

That is according to the scientific data. Glyphosate also has the cancer risk equivalent of drinking beverages above the temperature of 65°C.

After the IARC study, the EPA once again tracked a cancer risk assessment in 2017 on glyphosate, and found that glyphosate is “not likely to be carcinogenic to humans”.

There are many things in our environment that are known to be a risk for cancer. Cigarette smoking is one, and so is breathing in secondhand smoke.

So our Government’s ban on smoking within three metres of open-air eating establishments is lauded. I certainly don’t want to breathe in someone else’s smoke.

Alcohol is also a risk for cancer. So is breathing in too much vehicle fumes and living in a polluted area.

The most recent data is that your cancer risk increases if you drink hot tea nearing the temperatures of 100°C!

Glyphosate does not carry the risks of cancer that all these above products do. And if we are scientifically driven, the way doctors are, then we must go by evidence and evidence alone.


Dr YLM graduated as a medical doctor, and has been writing for many years on various subjects such as medicine, health, computers and entertainment. For further information, email starhealth@thestar.com.my. The information contained in this column is for general educational purposes only. Neither The Star nor the author gives any warranty on accuracy, completeness, functionality, usefulness or other assurances as to such information. The Star and the author disclaim all responsibility for any losses, damage to property or personal injury suffered directly or indirectly from reliance on such information.


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