dibenzopdioxins

Dibenzo-p-dioxins, commonly referred to as dibenzo-p-dioxins or dibenzodioxins, are a family of polycyclic aromatic compounds that consist of two benzene rings joined by two oxygen atoms in a 1,4-dioxin linkage. The parent compound is dibenzo-1,4-dioxin; numerous substituted congeners exist, with chlorine or other atoms replacing hydrogen. The term polychlorinated dibenzo-p-dioxins (PCDDs) is used for chlorinated derivatives.

Formation and occurrence: They form as byproducts of incomplete combustion, such as waste incineration, industrial processes involving chlorine, and certain metallurgical activities. They may also be produced in some natural processes. They are highly persistent in the environment, resistant to degradation, and are mobile in soils and sediments. They bioaccumulate in the food chain, especially in animal fats, leading to primary human exposure through diet.

Toxicology and risk: Dioxins are among the most toxic synthetic chemicals known. Toxic effects include skin lesions, immune and endocrine disruption, liver damage, and cancer in animal studies; human health effects are evaluated using toxic equivalency factors (TEFs). The 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is the reference congener with TEF of 1.0. The concept of toxic equivalents (TEQ) allows combining exposures to many congeners into a single risk metric.

Regulatory status: PCDDs are tightly regulated as persistent organic pollutants. International efforts include the Stockholm Convention on Persistent Organic Pollutants, which aims to reduce or eliminate emissions and releases. National programs monitor environmental levels and set emission limits for industrial sources; remediation efforts target contaminated soils and food chains.