PCDDs

Polychlorinated dibenzo-p-dioxins (PCDDs) are a family of polychlorinated organic compounds characterized by a dibenzo-p-dioxin structure with various chlorine substitutions. They comprise 210 possible congeners, most of which are not produced intentionally. PCDDs are highly persistent environmental pollutants formed primarily as byproducts of incomplete combustion and certain industrial processes, including waste incineration, chlorine bleaching, and metal processing. They resist degradation and can accumulate in soils, sediments, and fatty tissues of living organisms.

Toxicology and health effects are driven by activation of the aryl hydrocarbon receptor (AhR). The 2,3,7,8-tCDD congener is among the most toxic. Toxicity is commonly expressed as toxic equivalency (TEQ) using a set of TEFs (toxic equivalency factors), now often reported as WHO-TEQ. Exposure has been associated with cancer risk, immune and endocrine disruption, reproductive and developmental effects, and other adverse outcomes, depending on dose and congener profile.

Environmental fate and exposure pathways center on bioaccumulation in the food chain. PCDDs are lipophilic and tend to concentrate in animal fats, leading to dietary exposure as the primary source for humans in many regions. They can be transported long distances in the atmosphere and persist for years in soils and sediments.

Regulatory and remediation measures focus on emission controls and monitoring under international treaties such as the Stockholm Convention on Persistent Organic Pollutants. Emission reduction in industrial processes and waste management, along with treatment technologies like controlled high-temperature incineration and adsorption, are used to limit release and exposure. Measurement relies on high-resolution GC-MS analysis reported as WHO-TEQ.