Weed killers come in a liquid suspension to allow for easy application. The U.S. Environmental Protection Agency requires that no herbicide exceed toxicity levels based on testing of the active ingredient. To meet this requirement, inert ingredients are included: water and a surfactant to help thin the suspension so it can penetrate soil and effect weeds more quickly. The active ingredients differ greatly in function and appearance among brands.
Carfentrazone-ethyl is the active ingredient in Aim EC. It is a contact, selective herbicide capable of controlling broadleaf weeds less than 4 inches tall. It disrupts the cell membranes of the weeds, like sticking a pin in a balloon, effectively killing weeds at a cellular level. Carfentrazone is yellow-orange in color, viscous and has a faint but distinct petroleum smell.
EPTC's technical name is S-Ethyl dipropylthiocarbamate and is the active ingredient in Eptam 7-E and Eptam 20-G. It is a pre-emergent herbicide that blocks the synthesis of growth lipids in weed seeds, preventing them from germinating. Physically, it is a thin, pale yellow liquid with an aromatic odor similar to apple blossoms.
The patent for metolachlor is owned by a company that produces it under three names: Dual Magnum, Me-Too-Lachlor and Cinch. It is a pre-emergent herbicide that is ineffectual against weeds that have already sprouted. In weed seeds, it inhibits cellular division by increasing the rigidity of the cellular membrane. Because of this, the cellular membrane can't complete its mitotic stage and eventually dies. Physically, metolachlor is a blue-green, syrupy liquid with no noticeable odor.
Paraquat is marketed as Firestorm, but due to its extremely poisonous nature and the ease with which it is dissolved in water or food, it is not available to private citizens. It is a nonselective herbicide which destroys the chlorophyll production capacity of plant cells. With no chlorophyll, no photosynthesis takes place and the plant starves to death. Physically, paraquat looks just like black coffee, with no smell or taste. It is always dyed blue, given a sharp fecal odor and contains a vomiting agent to help prevent accidental ingestion.