Although there area a great variety of brand names for weed killers, the actual number of active chemicals used to produce these products is about 5. Most of these can be classified as a broadleaf herbicide, meaning that is will kill off plants that have a larger than average foliage component. Normally this would exclude grass, but on some occasions, manufacturers will add another component to the mixture, making it lethal to this substance as well. Usually the actual chemical name is listed first followed by a trade name. The first one or two on the label are the only ones that need to be examined, since many of the other ingredients are usually inert or used as fillers.

The first chemical is 2,4-Dichlorophenoxyacedtic Acid which is found in a variety of products, including Scotts Green Sweep, Ortho Weed B Gon and Triplex among others. These are of the weed and feed category, designed to kill off the unwanted lawn pests, while boosting the growth of grass. This substance is both a surface and groundwater contaminant. There can be problems with the endocrine gland in humans.

2-Methoxy-3,6-dichlorobenzoic acid (Dicamba) is found UltraStop Lawn Weed Killer, Scott's Pro-Turf and Tracker among others. It is classified as a broadleaf herbicide as well, with warnings from the EPA as a potential toxin. There is also evidence linking this chemical to non-Hodgkin's lymphoma.

2-Methyl-4-chlorphenoxy-propionic acid (Mecoprop or MCPP) is found in Menards Premium Weed & Feed, Mecomin-D and Kilprop products. It is also a broadleaf herbicide that has a number of different applications as well. The International Agency for Research on Cancer has identified this substance as a possible carcinogen for humans. Birds have also been show to be affected by exposure to this chemical substance.

2-Methyl-4-chlorphenoxyacetic acid (MCPA) is a component of Agritox, Envoy and Vacate chemical lawn formulas. It is often combined with the previous substance for additional strength. It is listed as a possible cancer causing agent along with being a surface and groundwater contaminant.

N-phosphonomethyl glycine glyphosate is a major ingredient in Ortho Ground Clear, Ranger and Pondmaster weed control applications. It is a broad spectrum herbicide that will kill grass and other plants. This chemical will leach from soil to contaminate ground water and is toxic to aquatic animals.

All of these substances kill weeds effectively, but should only be applied as per the instructions to ensure proper results are obtained and no side or collateral damage is done to your garden.