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Roundup Weed Killer Ingredients

By Laura Reynolds ; Updated September 21, 2017
Roundup keeps plants from putilizing nutrients.
weed image by Lytse from Fotolia.com

If you have ever done battle with brush, grassy weeds or poison ivy, you may have a bottle of Roundup in your garage. You possess a bottle of herbicide containing the most popular broad spectrum weed killer in the world--glyphosate. The Monsanto Company introduced glyphosate in 1974 and in 2010 marketed the herbicide to homeowners and farmers in 130 countries, much of it in the familiar bottle with the Roundup brand on its side.

Active Ingredient

Monsanto describes glyphosate on the Original Roundup label as N-(phophomethyl) glycerin in the form of its isopropylamine salt. The U.S. Forest Service Pacific Northwest Regions Pesticide Information Profile (USDAFS) lists the percentage of glyphosate in both forms tested as 41 percent. It is the only active ingredient listed in Roundup herbicides.


Roundup products contain a number of compounds designed to bind it to plant fatty acids, much as the surfactants in soap surround dirt and break its bond on a surface. Original Roundup contains polyethoxylated tallow amine surfactant. USDAFSs analysis of Roundup Pro found it to contain phosphate ester neutralized ethoxylated tallow amine surfactant. These phosphate esters of a tallow amine ethoxylate are called POEAs. Surfactants are classified as inert ingredients. They comprise approximately 15 percent of Roundup’s composition. In a study at the University of Caen reported in Scientific American in 2009, the surfactant POEA was singled out as dangerous to human embryonic, placental and umbilical cord cells. The French team concluded that the presence of certain inert ingredients can modify or intensify the toxicity of the active ingredient and that Roundup and other preparations should be considered as complete compounds rather than separated into active and harmless inert components.

More Inert Ingredients

The USDAFS lists other inert ingredients in Roundup or Roundup Pro as related organic acids of glyphosate, isopropylamine and water. The acids of glyphosate and isopropylamine, totaling no more than 2 percent, are added in varying percentages to some preparations; Roundup Pro does not contain them. This adjustment of the balance of salts and acids makes certain types of Roundup more effective on some plants, an important aspect for farmers who use the herbicide with crops. Water comprises 41.6 percent and 44.5 percent in Roundup and Roundup Pro respectively. POEA and the other inert ingredients in Roundup are also marketed separately as Entry II, a surfactant that is used with other herbicides.


About the Author


An avid perennial gardener and old house owner, Laura Reynolds has had careers in teaching and juvenile justice. A retired municipal judgem Reynolds holds a degree in communications from Northern Illinois University. Her six children and stepchildren served as subjects of editorials during her tenure as a local newspaper editor.