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Soil Toxicity of Roundup

lettuce image by carol lynch from

Roundup is a common herbicide that homeowners and others often use to control weeds and other unwanted plants. The active ingredient, glyphosate, is a chemical used in many other brands of herbicides as well as Roundup. Product claims include the statement that Roundup does not remain in soil where it is applied and that its presence in soil will not harm new plants when you plant them in the area shortly after using Roundup.

Product History

The Monsanto Company has manufactured Roundup since 1974, according to product literature. Roundup and other herbicides containing glyphosate are some of the most-used products of their type and are registered for use in over 130 countries. Roundup is a broad-spectrum herbicide that kills most types of green plants. Monsanto also states “glyphosate binds tightly to most types of soil so it is not available for uptake by roots of nearby plants,” but rather disrupts a plant enzyme that controls growth of the plant sprayed. The U.S. Environmental Protection Agency re-registered Roundup in 1993 and stated that when used according to label instructions, this product “would not pose unreasonable risks or adverse effects to humans or the environment.”

Acute Toxicity

According to the Pesticide Action Network of the United Kingdom, glyphosate’s acute toxicity is “very low.” They continue to state that this chemical can disrupt animals’ enzyme functions when they consume or come into contact with plants sprayed with this product. Glyphosate is “relatively harmless,” but other ingredients in Roundup and other herbicides containing this chemical are “less benign.” Surfactants are substances, such as polyoxy-ethyleneamine, that are added to spray products to help them adhere more effectively. Some surfactants are “serious irritants,” are toxic to fish and might cause cancer in humans. The Pesticides Action Network website includes a warning that people stay out of treated areas for 12 hours following application of Roundup.

Environmental Effects

Soil particles absorb glyphosate when it is sprayed in an area, which inactivates the chemical, according to the Pesticide Action Network. It then quickly degrades to carbon dioxide through the activity of soil microbes. When glyphosate is unbound, it degrades more slowly, which can cause it to remain in soil for years. When this occurs, the glyphosate inhibits anaerobic nitrogen fixation in the soil. Further, because glyphosate does not leach easily, it can move with eroded soil into ground water systems; in these environments, the rate of its breakdown is slow. When glyphosate is bound to soil particles it can stay active and the soil can release it to nearby plants, adversely affecting their health and growth.

Effect on Soil-Dwelling Creatures

Although glyphosate has been proven to be nontoxic to honeybees, it does harm earthworms and other soil-dwelling organisms, according to the Extension Toxicity Network at Oregon State University. The website reports that earthworms’ growth is stunted in soils that received repeated applications of glyphosate. The Extension Toxicity Network also reports that glyphosate is “moderately persistent” in soil and that is has an approximate half-life of 47 days. reports that Monsanto, the manufacturer, has determined that glyphosate can have a half-life of up to 141 days in soil. In most soils it is “strongly absorbed,” even if the soil has a low content of clay and organic materials.

Breakdown of a Metabolite in Soil

When glyphosate breaks down in soil, one metabolite is found. It is called AMPA, or aminomethylphosphonic acid. It is more persistent than glyphosate, having a half-life of up to 958 days. Although it has low acute toxicity according to, this metabolite causes several toxic reactions among laboratory rats. These include a decrease in the weight of the liver and excessive cell division in bladder linings. The site concludes with the information that AMPA has been found in crops such as barley and lettuce that were planted one year after the area was sprayed with Roundup or other herbicide containing glyphosate.

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