More than 200 brands of herbicide currently are sold on the open market in the United States. They are grouped into nine categories based on their active ingredient. Some are designed to kill all plants; some are focused on killing only specific species of weeds. Each categorical herbicide works on different principles, affecting plants in different ways. They affect human beings and other fauna in different ways, too.
Glufosinate-type herbicides affect all forms of plant life. They are absorbed through leaves and prevent plants from synthesizing glutamine, effectively starving the plant to death. This pesticide leaves no soil residue and degrades within five days of application, meaning there is no long-term danger. It is a neurotoxin that paralyzes or kills outright predatory insects exposed to it.
According to data collected by Dr. Joe Cummins of the University of Maine's agricultural division, human exposure has been shown to cause convulsions. Mammalian testing has shown apoptosis, or cell death, in the brains of embryonic mice. The offspring of male mice exposed to glufosinate show significant birth defects, while the offspring of exposed female mice show behavioral defects.
Arsenical herbicides kill on contact. Arsenic is toxic to any carbon-based life form, inhibiting cellular respiration and eventually resulting in cell death. In plants, this causes wilting and yellowing within seven days of application. As arsenic can be absorbed on contact with the skin, inhaled in dust or burned gas, or ingested, it is very dangerous. A 20-mg dose can be deadly to a full-grown adult and as little as 2 mg can kill a child.
Dr. Frederick M. Fischel of the University of Florida was cited in the text "Herbicide Activity" as confirming that immediate side effects include profuse sweating, numbness, a sensation of pins and needles, vomiting, diarrhea, muscle cramps, dizziness and severe headache. If treatment is not immediately received, symptoms progress to include grand mal seizure, coma, kidney failure and death.
Substituted Urea-Type Herbicides
Substituted urea-type herbicides are nonselective, affecting all species of plants. They are absorbed by the root body and subsequently inhibit the production of the root's primary growth enzyme, urea. It can take up to a month to see results, but this herbicide type stays in the soil, ensuring that plants do not grow back for years to come. It is considered one of the safest forms of herbicide to both animals and humans.
According to toxicology reports published in 1997 by Drs. R. Michael Roe, James D. Burton and Ronald J. Kuhr, when substituted urea-type herbicides are ingested in high quantities, it causes mild neurological depression, which is experienced as a mental fog. Long-term consumption can cause a slight increase in liver size and anemia. It should be noted that cats, having inefficient livers, find substituted urea-type herbicides fatal.