Dioxins is the popular name, but inaccurately, by which are known the polychlorinated-dibenzo-p-dioxins, called with the acronym: PCDDs. It is a group of 75 different substances characterized by a three ring structure, from whom two are benzenic joined by two oxygen atoms. It is important to underline that not all of these 75 compounds are toxic and dangerous. With a great difference, the 2,3,7,8 – tetraCDD (2,3,7,8 – TCDD) knowed as “the dioxin” is the most active toxicologically compound. 2,3,7,8 – TCDD is the synthetic compound most toxic that men have ever known.

Compuesto sintético más tóxico que el hombre conoce

TCDD were known since 1872, when were synthesized, but they remained as a lab curiosity, until 1957 when investigators make a relationship between TCDD and chloracne, described in workers who handled certain organic chlorinated products, and specially until the spread of the chick edema disease. An unknown disease affected a great number of poultry farms in the west and southeast of the USA in 1957. The basic symptoms were hydropericardium and generalized edema, hepatic necrosis and a high mortality rate. The studies that rapidly were initiated demonstrated that the toxic or the toxics were in the fats used to manufacture the feed and concretely in a byproduct contaminated with chlorphenols, organic products used as fungicides. Currently we know that in most countries the environmental levels of these substances increased dramatically in the forties, arriving to a maximum in the 1980s and nowadays are decreasing.

But, from a chemical and toxicological point of view, the “dioxins”  are so complicated because not all “dioxins” have the same toxicity. Related chemical compounds, but that are not dioxins, have “2,3,7,8 – TCDD” activity. These compounds are polychloninated-dibenzofurans or PCDFs and polychlorinated biphenyls (PCBs). In the figure we can see the basic chemical structure and the numeration of the rings and a  photo of chloracne’s lesions.

PCDDs and PCDFs have not ever been commercially manufactured, except in low quantities to do analytic or toxicologic studies. This is because of they are so toxic and dangerous. However, we’re in contact with PCDDs and PCDFs because they are produced inadvertently in different thermic processes as manufacturing or destruction of different organic chlorinated compounds, for example, when PVC plastics are burned.

PCDDs and PCDFs are ubiquitous substances. We can find them in the air, in the water, in the soil, in plants and in animals in small quantities, also, there are environmentally persistent and lipophilic, having the trending to bioaccumulation. This is why fatty food from animal origin are the main source of these compounds. In fact it is calculated that diet supplies 90-95% of the total PCDDs and PCDFs, being the fish, the poultry, the bovine meat, the milk and the dairy products the main sources.

Dioxins are well established carcinogens in animal studies, although the precise mechanistic role is not clear. The International Agency for Research on Cancer has classified TCDD as a human carcinogen (class 1). The symptoms reported to be associated with dioxin toxicity in animal studies are incredibly wide ranging. Acute effects of single high dose dioxin exposure include wasting syndrome, and typically a delayed death of the animal in 1 to 6 weeks. Dioxins have been considered highly toxic and able to cause reproductive and developmental problems, damage the immune system, interfere with hormones and also cause cancer. The best proven is chloracne.