French President Emmanuel Macron has declared he will ban the American herbicide glyphosate within three years, and sooner if a replacement is ready. Italy has vowed to do the same. Activists have said the replacement is already available, and it has been used in France since 1863 - a fatty acid called pelargonic (a.k.a. nonanoic, because of the nine carbon atoms) acid. Chemically, it's pretty close to a soap. Does this make any sense toxicologically? Is this another case of "natural = safe?" Or is something else going on? Let's take a look at the toxicological and environmental properties of both chemicals.
First, a qualitative look at safety
For a quick and dirty way to get a rough idea of the toxicity of a chemical, the National Fire Prevention Association (NFPA) maintains an enormous database of tens of thousands of chemicals. It is always a good place to start. A fire prevention database? Yes, because first responders need to know on a practical level what they're dealing with in the event of a chemical spill or fire, no endocrine disruptor or parts per billion nonsense. It classifies chemicals by toxicity, flammability, and water reactivity. Chemicals are placed into five toxicity categories, zero through four. In categories zero and one are things like salt, water, and baking soda. Harmless.
Figure 1. NFPA safety diamonds
Group 2 hazards, where these two both reside, are slightly worse.
"Intense or continued exposure could cause temporary incapacitation or possible residual injury unless prompt medical attention is given." - NFPA definition of a Group 2 toxin. (1)
Members of this group include ether, benzaldehyde (almond oil), butyric acid (in rancid butter), and hydroquinone (skin bleaching agent). Like vinegar, you wouldn't want to drink a glassful, but they are unlikely to do serious harm with normal exposure.
Both pelargonic acid and glyphosate are characterized as Group 2 chemicals for acute issues but there is more to overall toxicity than a diamond will tell you so let's look at the animal toxicity data. One important parameter is called the LD50 and that is the dose at which half the animals will die. The lethal dose data of pelargonic acid and glyphosate in animals is interesting...because they are both uninteresting. Neither compound has any appreciable acute toxicity.
Figure 1. Relative toxicity glyphosate and pelargoic acid. See below for references.
By comparison, the LD50 values in rats for aspirin, caffeine, and alcohol are approximately 200, 192, and 7000, respectively. Caffeine and aspirin are significantly more toxic than either herbicide. Alcohol is similar.
So neither glyphosate nor has worrisome acute toxicity in animal models. But what about the scary stories that environmentalists tell regarding glyphosate? Ignore the hysteria. It is one of the most thoroughly studied chemicals of all time because it is one of the top chemical boogeymen for environmental activists. While there are numerous methods for determining toxicity, carcinogenicity, etc., it doesn't cause cancer, even though IARC claimed it probably did and was even jeered by its own bosses at the United Nations for shoddy, agenda-driven work. (See "Glyphosate-Gate: IARC's Scientific Fraud," my colleague Alex Berezow's exposé of glyphosate here.)
Both chemicals are so non-toxic that it would be impossible to eat enough of either to harm yourself unless you were really, really trying.
What about the environment?
Neither chemical poses much of a risk to the environment. According to Marin Municipal Water District Herbicide Risk Assessment:
- "Glyphosate poses... low risks to aquatic species. (Chapter 3, Glyphosate)"
- Pelargonic acid poses low risks to ... aquatic and terrestrial wildlife. (Chapter 7, Pelargonic acid)
Although the magnitude of toxicity of pelargonic acid and glyphosate toward various fish both vary according to species, it is important to note at these low concentrations neither is harmful. Both products are approved for agriculture and even for human consumption at concentrations found in drinking water:
- "Glyphosate poses the least risk to workers and the general public,"
- "Pelargonic acid poses low risks to workers [and] the general public..."
Yet you'd never know any of this according to some activists. activists, which declare glyphosate harmful and pelargonic safe even though they are toxicologically similar. The Cleveland Museum of Natural History states "[T]he most common fatty acid, pelargonic acid, is considered to have very low toxicity and to be environmentally friendly" while also declaring glyphosate a cause of cancer.
How about cost?
With regard to expense, the material cost of the alternative herbicides was more than the conventional herbicides, sometimes substantially more. The need for repeated applications of the alternative herbicides further increases the costs of their use
Source: "Herbicide Alternatives Research" Department of Plant, Soil, and Insect Sciences University of Massachusetts
Alternatives like pelargonic acid cost more. How much more? A whole lot, according to the New York State Department of Transportation:
"Scythe (57.0% pelargonic acid a.i.) was mixed with water at a 10.0% volume to treat the guiderails along the entire 8-mile section of Route 80, from mid-morning to mid-afternoon on July 22, 2014. ... Total area of treatment was 1.48 acres... Treatment costs were $1,954 based on materials alone."
Compare that to:
"In comparison, estimated cost of Materials and Methods 3-3 materials for conventionally treating the same area using Accord XRT II herbicide (synthetic glyphosate as active ingredient) would have been $18.24 total."
A lot more chemicals will be needed
Even if they are about the same toxicity, pelargonic acid requires a lot of more chemical, which means more runoff, which most environmentalists should be against. Pelargonic acid will only kill the green parts of the plant they contact, so most treated plants are able to recover because the roots remain intact. Glyphosate and products like 2,4-D work better with far fewer applications they go to the roots to kill larger plants and perennial weeds.
Does *anything* about French and Italian politics make sense here? Neither herbicide has any appreciable mammalian toxicity, that's good, but the "organic" pelargonic acid costs 100-times more and it works less on weeds.
If you're a farmer in France you may have no choice than to use it but if you're anywhere else and decide to switch to pelargonic acid simply because it is "natural" you may want to think twice. Instead of growing food you may end up selling it. At McDonalds.
(1) Group 3 chemicals are to be avoided. Some of them are very nasty. Some group 4 chemicals can kill you immediately.
- (a) https://www.fishersci.com/shop/msdsproxy productName=AC258260010&productDescription=NONANOIC+ACID%2C+98%2B%25(GC)+1KG&catNo=AC258260010&vendorId=VN00032119&storeId=10652
- (b) https://toxnet.nlm.nih.gov/cgi-bin/sis/search/a?dbs+hsdb:@term+@DOCNO+5554
- (c) https://www.marinwater.org/DocumentCenter/View/252
- (d) https://toxnet.nlm.nih.gov/cgi-bin/sis/search/a?dbs+hsdb:@term+@DOCNO+3432