2,4-dichlorophenoxyacetic acid (2,4-D) is a widely used synthetic herbicide. It affects only “broadleaf” plants (typically the plants we consider weeds) and not grasses or most crops, hence it can be widely applied without harming desirable vegetation. This chemical mimics natural plant hormones and causes rapid, uncontrolled growth of broadleaves, leading to death of the plant. Pure 2,4-D is actually relatively insoluble in water and so other forms, such as esters and salts, are now more widely used.
2,4-D is applied so commonly that a 2003 study found that 63% of homes contained traces of this chemical in household dust! It was also a component of the infamous Agent Orange herbicide used during the Vietnam War. Exposure of military personnel to Agent Orange was subsequently connected to a wide variety of health problems. Currently, it is believed that these health issues were actually more likely due to the presence of other chemicals present in Agent Orange, such as traces of dioxin.