245T

2,4,5-T, commonly written as 245-T, is an organochlorine herbicide and synthetic auxin (a plant growth regulator). It has been used to control broadleaf weeds in agriculture, forestry, and rights-of-way, typically in combination with 2,4-D to broaden its spectrum of activity.

Chemistry, production, and use: 2,4,5-T was developed in the mid-20th century and became widely used from the 1950s through the 1980s. It was manufactured commercially by several chemical companies and served as a key component in several defoliant formulations, including Agent Orange used by the U.S. military during the Vietnam War.

Hazards and environmental fate: A major public health concern with 2,4,5-T arises from dioxin impurities, particularly TCDD, that can form during manufacturing. Dioxins are highly toxic and persist in the environment, with associations to cancer, chloracne, and reproductive or developmental effects. The herbicide itself acts as a synthetic auxin, causing uncontrolled growth and plant death. In the environment, 2,4,5-T and its residues can persist in soils for years, with degradation occurring slowly through photolysis and microbial processes and potential bioaccumulation in some organisms.

Regulation and legacy: Due to health and environmental concerns, many jurisdictions restricted or banned 2,4,5-T in the 1980s and 1990s, with the United States phasing out most uses during that period. Internationally, restrictions or bans followed in several countries. Legacy contamination from earlier production remains a topic of environmental monitoring and, in some cases, remediation efforts.