The Toxicity of Weed Killer


Roundup and Rodeo are popular weed killer products advertised for home use. They are said to be harmless, but recent studies show that they may cause cancer and cell abnormalities. Glyphosate is the main ingredient of weed killers. It is the "inert ingredients" in combination with glyphosate that pose the greatest health risk. You can avoid the use of toxic weed killers by practicing preventative weed control techniques.


Glyphosate was developed and patented by the Monsanto international pharmaceutical company in 1976 and sold as Roundup weed killer. The company had previously patented the toxic pesticide DDT and the toxic defoliant Agent Orange in the Vietnam War era. Agent Orange was subsequently found to cause three types of cancer and elevated levels of spina bifida in veteran's children, according to the United States Institute of Medicine.

Health Effects

The U.S. Environmental Protection Agency (EPA) identifies glyphosate as toxicity class II, which is moderately toxic. Negative health effects are considered minor; including headaches, breathing problems and other flulike symptoms. Weed killers such as Roundup and Rodeo have been accepted as harmless on the strength of this identification. The "inactive ingredients" in weed killer products did not come under scientific scrutiny until a study at the University of Caen, France, as reported in the June 23, 2009 issue of Scientific American.

Inert Ingredients

Inert ingredients are considered trade secrets and not subject to laws about toxic chemicals. One specific inert ingredient of Roundup weed killer, polyethoxylated tallowamine (POEA), was found to cause cell abnormalities in placenta, umbilical cord and human embryonic cells in combination with glyphosate. University of Caen researchers "suspect that Roundup might cause pregnancy problems by interfering with hormone production, possibly leading to abnormal fetal development, low birth weights or miscarriages."


The EPA reports that weed killers such as Roundup are not toxic when used as directed. Hundred of studies confirm that their toxic effects are within the allowed range for human exposure. POEA is also considered safe, even in USDA certified organic products. "The authorizations for using these Roundup herbicides must now clearly be revised since their toxic effects depend on, and are multiplied by, other compounds used in the mixtures," according to the French researchers.

World Studies

The Scientific American article cites reports from other countries about potential toxic effects of Roundup weed killer. A high incidence of birth defects and cancer was reported in people living near sprayed cropland in Argentina, and a court ban on the chemical glyphosate has been sought by scientists. Scientists there also linked genetic malformation in amphibians to glyphosate exposure. A Swedish study reported in the article also identified a link between weed killer exposure and non-Hodgkin lymphoma.

Keywords: toxic weed killers, Roundup toxicity, herbicide poisons

About this Author

Joan Norton, M.A., is a licensed psychotherapist and professional writer in the field of women's spirituality. She blogs and has two published books on the subject of Mary Magdalene; "14 Steps To Awaken The Sacred Feminine:Women in the Circle of Mary Magdalene," and "The Mary Magdalene Within."