Pesticide Blog Post: Glyphosate

The Basic (Bai, 2016), (Heap, 2017):

Glyphosate [N-(phosphonomethyl) glycine] is the widely utilized herbicide in the world. It is known for efficiently destroying weeds at low cost as well as its perceived low toxicity, rapid absorption by plants, and slow evolution of glyphosate resistance in weeds. In 2011, it received 5.5 billion dollars in sales and a global demand of approximately half a million tonnes per year. It is adopted in soybean, corn, cotton, canola and sugarbeet due to its effectiveness in glyphosate-resistant crops combining with its broad spectrum of control at a relatively cheap cost.

Image source found here

Mechanism of Action (Bai, 2016):

Glyphosate is a non-selective, systemic, post emergence herbicide which inhibits enzyme 5-enolphyruvylshikimate-3-phosphate synthase (ESPS) in the shikimate pathway, which produces aromatic amino acids utilized for the production of proteins and plays a key role in the production of secondary metabolite; lignin. This inhibition restricts the shikimate pathway causing uncontrolled carbon flow and depletes compounds needed for carbon fixation, this ruins organisms metabolism.

Image source found here

Side Effects, Signs and Symptoms of Glyphosate:

Toxicokinetics (cdc.gov):

• Glyphosate is easily absorbed through the gastrointestinal tract; not lot of glyphosate gets absorbed through the skin and is assumed to get easily absorbed through the respiratory tract.
• Glyphosate does not get gathered up in any specific organ or tissues but is easily distributed by the blood.
• Glyphosate does not go through significant metabolism in mammals; less than 1% is metabolized to aminomethylphosphonic acid (AMPA).
• 2/3 of an oral dose is excreted in the feces as parent compound that is unabsorbed. Almost all the glyphosate is quickly excreted in urine as parent compound.

Figure 1: (cdc.gov) Image source can be found here
Pgs.: A-12 – A-14.

Summary: This figure depicts the most sensitive endpoint being gastrointestinal die to its oral chronic-duration of laboratory animals to glyphosate. Inflammation of gastric squamous mucosa was observed in female but not male rats. Even though salivary gland cytoplasmic changes were eminent in rats, theses changes were only of little or mild severity and are not considered adverse effects.

 

Biomarkers (cdc.gov):

Glyphosate and its metabolite AMPA have been found in blood and urine, but most absorbed glyphosate is easily excreted as parent compound and urine is usually considered to be a stronger biomarker of exposure because level of detection is lower than blood. Best quantification would require immediate analysis of blood and urine within hours of exposure.

Treatment (Bradberry, 2004):

• Gastric lavage is an option for someone who has ingested life-threatening amount of a concentrated glyphosate formulation within 1 hour.
• Appropriate use of crystalloids, colloids and blood products can be used to treat hypotension and fluid loss.
• Most severe poisoning likely requires intubation and mechanical ventilation.
• Sodium bicarbonate can be used for significant acidosis.
• Electrocardiogram should be performed in all symptomatic cases.
• Skin contamination can be managed by removal of contaminated clothing and washing with soap and water.
• Eye contamination should be managed with sufficient irrigation.

Resources:

1.) Bai SH, Ogbourne SM. Glyphosate: environmental contamination, toxicity and potential risks to human health via food contamination. Environ Sci Pollut Res Int. 2016 Oct;23(19):18988-9001. doi: 10.1007/s11356-016-7425-3. Epub 2016 Aug 19. PMID: 27541149.

2.)Heap I, Duke SO. Overview of glyphosate-resistant weeds worldwide. Pest Manag Sci. 2018 May;74(5):1040-1049. doi: 10.1002/ps.4760. Epub 2017 Nov 29. PMID: 29024306.

3.)Toxicological Profile for Glyphosate – Draft for Public Comment (cdc.gov)

4.)Bradberry SM, Proudfoot AT, Vale JA. Glyphosate poisoning. Toxicol Rev. 2004;23(3):159-67. doi: 10.2165/00139709-200423030-00003. PMID: 15862083.