2378tetrachlorodibenzodioxin

2,3,7,8-Tetrachlorodibenzo-p-dioxin, commonly abbreviated as TCDD, is a highly toxic chlorinated dibenzo-p-dioxin. It is not manufactured for commercial use but is formed as a byproduct in certain industrial processes, including chlorine bleaching of pulp, combustion of chlorine-containing materials, and the production or use of some herbicides in the past. TCDD is regarded as one of the most toxic synthetic organic compounds known to science.

Chemically, TCDD consists of two benzene rings joined by a central dioxin ring and bears four chlorine atoms at the 2, 3, 7, and 8 positions. Its chemical formula is C12H4Cl4O2, and its molecular weight is about 322 g/mol. The molecule is highly lipophilic and extremely persistent in the environment, resisting natural degradation and remaining in soils, sediments, and fatty tissues of organisms for long periods.

TCDD exerts most of its effects through binding to the aryl hydrocarbon receptor (AhR), triggering changes in gene expression that can disrupt development, immune function, and hormone signaling. It is associated with chloracne, liver toxicity, immune suppression, and an increased risk of certain cancers in humans. Due to its potency and persistence, exposure is primarily a concern from contaminated food sources and long-range environmental transport.

Regulatory and environmental aspects: TCDD is classified as a persistent organic pollutant and is subject to international controls under the Stockholm Convention. Emission reductions, monitoring, and remediation efforts aim to limit human and ecological exposure, given the compound’s long-term persistence and bioaccumulation.