Sarah Hovinga

How Is Sugar Similar to Glyphosate?

For this blog, I want to talk about Toxicity. No, this is not the name of my new rock band, but rather an important fundamental concept to how we think about the safety of agrochemicals.

Have you ever heard the saying that everything has the potential to be toxic in the right dose? It’s the dose that makes the poison? In large part, this is true. For example, even something that is thought of as benign as water can be toxic for us as humans if we ingest too much. This highlights the concept of concentration. Now, let’s think of another type of commonplace ingredient in our kitchens: sugar. A spoonful of sugar seems pretty innocent, right? Maybe on average for humans, but did you ever wonder why sugar doesn’t spoil? It’s because in a solid form like we buy from the grocery store, it’s toxic to microorganisms that would otherwise decompose it.

Most substances have a measure of their toxicity to types of organisms, common chemicals like sugar and agrochemicals included. Usually this number is reported in some sort of dose (or concentration) and its effect on a population, such as “LD50”, which stands for the lethal dose that will affect 50% of a population. For example, if a scientist tells you a certain chemical has a high LD50 value it actually means it is less toxic than something with a low LD50 because with the latter, it took less of the substance to affect the population. So if “compound A” has an LD50 of 10,000 and “compound B” an LD50 of 10, that says that compound B is 1,000 more potent than compound A.

Sarah Hovinga, Senior Scientist, Biologics Project and Product Support, Disease Management, Bayer Division Crop Science
Sarah Hovinga, Senior Scientist, Biologics Project and Product Support, Disease Management, Bayer Division Crop Science
Sarah Hovinga,
Senior Scientist, Biologics Project and Product Support, Disease Management, Bayer Division Crop Science
A chart comparing the LD50 values of chemical substances.
A chart comparing the LD50 values of chemical substances.
A chart comparing the LD50 values of chemical substances. (Source)

Now, would you believe that some common chemicals we live with everyday vary dramatically in LD50 values? Our friends water and sugar fall into the category with the highest LD50 values, meaning they have very low toxicity. Table salt (Sodium chloride) hangs out with hydrogen peroxide in the slightly toxic category. Then there’s caffeine and lead. They are in the same LD50 category (weird, huh?) and are considered moderately toxic. And finally we have vitamin D3 and nicotine which are both considered highly toxic. Again, all of this should be taken into the context of it’s the dose that makes the poison. Personally, I ingest water, sugar, table salt, caffeine, and vitamin D every day, but I’ve got the dose right. How does this relate to agrochemicals?

Agrochemicals are tested for their LD50 values too in order to determine their toxicity. This value, among many other measurements, helps to determine several important considerations for their impact on human health and thus, how they should be used when protecting crops. Now here comes the interesting part. Glyphosate, a common conventional herbicide, is in the same category as sugar and water. Spinosad, an organic insecticide, is in the same category as table salt. And copper sulfate, an organic fungicide, is in the same category as caffeine. When compared in this way, I know it gave me a different perspective on chemical substances, whether they were in my kitchen or on my lab bench. An important point to remember, however, is that all agrochemicals have labels that legally need to be adhered to by anyone handling them when it comes to their approved use and safety.

It goes without saying that this is just the beginning of where the conversation should start when determining important agricultural regulations such as residue limits on foods (known as Maximum Residue Limits) or the minimum time someone must wait to re-enter a field after it’s been treated (called a re-entry interval). These values are known for each chemical used in agricultural production, already regulated for, and when compared to items we are around every day, at least based on the toxicity values we’ve been discussing, they don’t differ radically. Everyday objects around us pose threats and it’s the knowledge and awareness that matter in terms of how we interact with those objects.

For some more reading on this subject, I’ve found a couple sources interesting which explain some of these concepts more that I list below.

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A scientist
July 07, 2018 - 03:24 AM

1. LD50 is the wrong way to think about the toxicity of chemicals. What about more persistent compounds that build up in tissues over an organisms lifetime. DDT is banned in most countries for exactly that reason. But, according to your chart, not much deadlier then caffeine. Bald eagles feel that DDT, is pretty lethal.
2. LD50 measurements assume a healthy organism. For example, individuals with diabetes won't have the same LD50 for sugar. The same may apply to any compound, including pesticides.

As a scientist, you have a responsibility to not mislead the public with technically true but misleading articles such as this.

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Sarah Hovinga
July 10, 2018 - 02:18 PM

Hello fellow scientist and thank you for your interest in my blog. I would add onto your comment by saying that it’s not only my job to inform people on the most accurate information that I have based on literature and experience, but I also feel it’s my moral obligation as a human. So absolutely agreed. That is one of the reasons why I started this blog in the first place. Here is my first post to read a little more on that in case you are interested in who I am:

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Sarah Honvinga
July 10, 2018 - 02:10 PM

LD50s and acute toxicity (the topic referenced in this particular blog) is only a starting point for how we should think about regulating agrochemicals, as I mention in my post. These values are based on scientific studies, are accurate, and should be one of the first steps in determining toxicity. You obviously have advanced knowledge in toxicity, and so what you’re referencing in your point #1 is chronic toxicity, which comes after the acute tests, of course. This is why I included some further reading on this topic from a blog I found very interesting; you probably would too.

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Sarah Hovinga
July 10, 2018 - 07:50 AM

I think it discusses the balance of acute and chronic toxicities well and would be good follow-up to someone interested in learning more on this point. I post it again here just for ease: It has the same chart as with acute toxicity but for chronic, so it’s interesting to compare.
The #2 point you bring up about DDT is a good one too, since it highlights the importance of specificity. It’s actually the breakdown product of DDT, DDE, that affects birds’ eggshells.

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Sarah Hovinga
July 10, 2018 - 07:49 AM

What is harmful to birds, something like DDE, for example, is not necessarily harmful to humans. And this of course goes across all living things on the planet. And even if a substance is harmful to humans, doesn’t mean that it will affect all humans the same, so specificity also needs to be determined (and is) in agrochemical testing.
I’m glad we share the same passion of looking into the science on topics like these. Thanks for the conversation.

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