6 of 17 – Is Glyphosate an especially dangerous pesticide?


GUEST AUTHOR: Iida Ruishalme |@Thoughtscapism

Iida Ruishalme is a writer and a science communicator who holds an M.Sc. in Biology from Sweden. She thinks nature is pretty awesome, and that it only gets more awesome the more you learn about it.

[ A version of this essay previously appeared on Thoughtscapism. ]


There are many pesticides that have been in use for hundreds of years which carry clear potential for harmful effects for the consumers, such as lead arsenate and other arsenate compounds. The use of these, luckily, has largely been banned or discontinued between 1950s and 1980s. Other pesticides, such as DDT and 2,4,5-T (responsible for much of the ill effects in Agent Orange), were introduced around last mid-century and also became banned a few decades later after clear evidence of harm to humans or the ecosystem had surfaced. The substances introduced during this time (when regulation was non-existent, as outlined above) are probably responsible for much of the reputations pesticides still carry today.

But most of the pesticides in use today are significantly less toxic than those used even a few decades ago, and despite what many might think, glyphosate is actually among the safest of the bunch. If you look at the doses that have proven lethal to half of the laboratory animals tested, the so called Lethal Dose 50 (LD50), you find that some of the most common organic herbicides, such as clove oil, acetic acid, and cinnamon oil, are also more toxic than glyphosate. In fact, when it comes to the lethal dose, even table salt is more toxic than glyphosate (see table below: 3000 vs 4900 mg/kg – toxicity studies on glyphosate LD50 can be found at EPA here, and studies determining the No Observable Adverse Effects Level (NOAEL) here). Other common substances and their LD50 values described here.

This doesn’t mean we don’t have to be careful about glyphosate’s effects – we wouldn’t want to sprinkle salt or concentrated plant oils on our fields either without a good understanding of the consequences.

Screen Shot 2016-09-02 at 09.31.02

University of Florida Pesticide Information Office compared the toxicity of herbicides and household chemicals. The lower the LD50 (dose at which half of lab animals die) value, the more potent the toxicity of the compound. Glyphosate (LD50 4900) is less toxic than table salt (LD50 3000).

In fact there is a lot more focus on what consequences there are to using pesticides than there used to be. DDT, 2,4,5-T, and lead arsenate have been banned. Farmers in the US no longer treat apple orchards with arsenic-containing pesticides (which still contaminate the grapes of some wineries growing in their place, and whose use continued for longer in other countries, such as China).

Photo by Aqua Mechanical
| Flickr | CC license

This switch to less toxic pesticides, which Alison Bernstein also talked about above, is part of a process which many consumers may not be aware of. During the past several decades, science and regulatory agencies have moved modern agriculture away from persistent and acutely toxic substances. Milder, more targeted, and much less generally toxic pesticides have replaced older, harsher agents. Thanks to wide adoption of Integrated Pest Management and biotech crops, overall pesticide use is also down.

Agricultural scientist and journalist Steve Savage has written in detail about the kinds of pesticides in use today. Using pesticides in California as his example, he illustrates the major shift toward essentially non-toxic substances, and he compares changes in amounts and toxicities of pesticides used between 1990 and today. He writes:

Most pesticides today have oral ALD(Acute Oral Toxicity)50s of more than 5,000 mg/kg (Category IV) and are less toxic than table salt, vinegar, citric acid, vanillin and many other familiar food ingredients.

University of Florida Pesticide Information Office has also put out a report on this trend towards much more harmless herbicides, called Herbicides: How Toxic Are They? In it, they write:

Although there have been pesticides that were toxic and dangerous to handle, most of these products are no longer used and have been replaced by newer chemistry. Pesticides now must go through rigorous testing by the U.S. Environmental Protection Agency (EPA) before they can be sold. This has led to many herbicides that possess little or no mammalian toxicity and are less harmful than many everyday household products (Table 1). Surprisingly, household chemicals that many of us store under the kitchen sink pose more risk to the handler than herbicides.

For other comparisons, see the excellent piece here by Cami Ryan: The Dose Makes the Poison. Her table also illustrates that rotenone (rarely used in organic farming) and copper sulphate (very common in organic farming) are much more toxic than glyphosate. This begs the question, why are so many people worried about glyphosate, and not other, more toxic pesticides?

The Credible Hulk has written a piece documenting the effects of many of the pesticides which glyphosate has directly helped make redundant, many of which we would need to resort to again, should glyphosate become banned in the EU. What we need to consider, is which of the known risks are larger. In his piece, The Credible Hulk writes:

Many people never even hear about the herbicides that were phased out in favor of glyphosate simply because they aren’t pertinent to the anti-agricultural biotech narrative, and because their popularity had waned by the time it had become trendy to demonize GMOs and everything remotely associated with them.
[…]
Weeds are a legitimate problem in farming that has to be dealt with one way or another. In its absence, it would have to be replaced with something else, and it would likely be something more harmful: not less.

TeroVesalainen | Pixabay | CC license

The important question is whether there is a realistic basis to worry about a risk – any risk, not just glyphosate. Why should we single out glyphosate as more risky than something else? What about the risks of not using glyphosate (more about that in section 13. Glyphosate and The Environment)? In life we rarely choose from a scenario where there is only the risk of one thing to consider. Choosing not to do something has different consequences, and also carries a risk. Which choice should we apply precautionary principle on?

The best way to find guidance to that question is to rely on the collected wisdom of the best and most comprehensive recent reviews on the research. At present, they show that used appropriately, glyphosate is a very safe option for weed control, with many benefits and little risk.


If you are interested in other environmental or health topics, you can find my other pieces on glyphosate over at 17 Questions about Glyphosate, and further resources under Farming and GMOs, The Environment, and Vaccines and Health. If you would like to have a discussion in the comments below, please take note of my Commenting policy. In a nutshell:

  1. Be respectful.
  2. Back up your claims with evidence.

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