Phenoxy Acid Types

• Mecoprop (MCPP) and 2,4-D chemical compounds are used in systemic weed killers applied as a spray. The plant absorbs phenoxy compounds and translocates them to younger tissues, causing twisting, yellowing and death. They are not classified by the EPA as restricted use pesticides. According to Beyond Pesticides, an environmental informational group, 2,4-D has been linked to cancer, endocrine disruption, reproductive toxicity, kidney/liver damage, and toxicity to pets and wildlife.
  
  

Dinitroaniline Types

• Pre-emergent weed killers inhibit cell division and prevent root growth of germinating seeds. Chemicals found in this class of weed killer include pendimethalin, trifluralin, benefin and prodiamine. Trifluralin is rated a Class 3 -- slightly toxic -- chemical but has been implicated as a possible cause of breast and other types of cancer. The Beyond Pesticides organization identifies pendimethalin as damaging to kidneys, liver, the reproductive system and the endocrine system.
  
  

Glyphosate

• Glyphosate weed killer is the most widely used in public parks, home gardens and nonorganic farms. The chemical glyphosate is categorized as nontoxic as a single ingredient, but the inert ingredients in commercial products have a toxic synergistic effect. Inert ingredient chemicals in weed killer products are considered trade secrets and protected by law. Glyphosate and its inert ingredient chemicals have been found to cause cell abnormalities and other reproductive damage by the University of Caen, France.
  
  

Diquat

• Diquat is the active chemical agent in many nonselective contact weed killers. It damages plant cell membranes and interferes with the photosynthesis process, producing quick wilting and death. Diquat weed killers desiccate all plants they come in contact with. Diquat is a Class 2 pesticide considered "moderately toxic" by the EPA. It is toxic to birds and fish. Diquat is damaging to the liver, kidney and reproductive system.