From the dioxin of Seveso, one of the most serious industrial accidents in Italian history, to Agent Orange in Vietnam, some lessons have been drawn. Here is where dioxin is found today, what proven effects it has on humans, the environment and health, where it has been banned and where it still exists.
Dioxin is the common name used to refer to dibenzo-p-dioxins and dibenzofurans. It is a group of chemically related compounds that are persistent organic pollutants (POP – Persistent Organic Pollutants). One should really speak of dioxins, in the plural, because 210 different types of compounds with similar characteristics and toxicity are in fact known, comprising dioxins – 73 types – and furans. They are formed from aromatic hydrocarbons bonded to chlorine atoms. The term dioxin is currently used as a synonym for TCDD, or 2,3,7,8-tetrachlorodibenzo-p-dioxin. These are molecules that are toxic to humans, animals and the environment. Other substances also possess toxicity characteristics similar to those of dioxins, such as PCBs (polychlorinated biphenyls, which made headlines in 1999 over the contaminated chicken and egg scandal) and PCPs (polychlorophenols).
These are persistent organic pollutants. If TCDD dioxin leaches into the soil, it binds to the organic matter present and degrades very slowly, over the course of decades. Among dioxins, TCDD is the most markedly toxic molecule: it causes a wide range of effects, including cancers, toxicity affecting the immune system, liver and skin, as well as mutagenic and embryotoxic action. The most recent findings on the mechanism of action of dioxin have clarified its role as a hormonal and endocrine disruptor, with all the serious implications that follow.
Dioxins are found (unfortunately) all over the world, in the environment, and accumulate in the food chain, primarily in the fatty tissue of animals.
More than 90% of human exposure is through food, particularly meat and dairy products, fish and shellfish. Many national authorities have programmes in place to monitor the food supply.
Dioxins are highly toxic and – with prolonged exposure – can cause reproductive and developmental problems, damage the immune system, interfere with hormones and also cause cancer.
Because of the ubiquity of these substances, all people in the world are subject to background exposure, which should not affect human health. "However, due to the highly toxic potential – the WHO notes – every effort must be made to reduce current background exposure."
The best way to prevent or reduce human exposure is through measures at the direct source, that is, rigorous control of industrial processes to reduce dioxin formation. And, of course, avoiding the burning of plastic waste.
Dioxins and furans form as (unwanted) by-products in the industrial production of chlorophenoxy herbicides (such as 2,4,5-trichlorophenoxyacetic acid, also known as "Agent Orange", a Monsanto defoliant used in the Vietnam War) or of synthetic disinfectant compounds (hexachlorophene, trichlorophenol). These are processes that take place at high pressure and temperature, with all the risks of raising temperature and pressure in reactors in an uncontrolled manner, of generating considerable quantities of dioxin and of causing the pressure-relief valves to blow open: this was the cause of the accidents at Bolsover in England in 1971 and at Seveso in 1976.
At Seveso, a cloud of TCDD weighing a few kilograms was dispersed into the environment on 10 July 1976. The fallout caused the contamination and evacuation of a vast urban area, the death of thousands of domestic animals, and consequences for the local population that will be the subject of study and debate for a long time to come.
In 1971 at Times Beach (Missouri), large quantities of waste oil were sprayed to prevent dust from rising from unpaved roads and horse-riding arenas: the oil was contaminated with reactor residues containing high quantities of dioxins from a herbicide production plant. The consequences were: widespread deaths of domestic animals (including 72 horses) and wildlife, accompanied by several cases of chloracne in children. The town of Times Beach was evacuated in 1981 due to the ineffectiveness of decontamination efforts (Environmental Research Foundation, 1991).
One of the greatest food scandals in modern history dates to 1998: dioxin-tainted chickens, eggs and ham. In Belgium (and beyond), factory-farmed chickens and pigs had begun to be fed animal feed supplemented with used machine oil, in order to "enrich" its consistency. The result was a Europe-wide withdrawal of food products contaminated with PCBs, the exposure of thousands of consumers to levels dangerous to their health, and a rethink of food policy and farming methods.
The scandal began on 28 May 1999 when the Belgian government issued a communication on the presence of PCBs, a dioxin precursor, in chickens and eggs. There had been previous cases in the USA (350 poultry farms closed in 1997 due to dioxin in bentonite, a feed additive) and in France (in 1998 some incinerators had contaminated pastures in the north of the country), but this time the contamination was not accidental. PCB is a component of engine oils, transformers, capacitors and electric motors. The animals were being fed with feed containing used mineral oils and fuel residues.
In the decade 1930–40, following the discovery of how to bond chlorine to petroleum-derived hydrocarbons, large-scale industrial production of solvents, pesticides, disinfectants and plastics got under way. The chlorinated compounds formed through industrial processes and combustion release certain unwanted by-products: dioxins.
Within a few decades, hundreds of thousands of tonnes of PCBs (polychlorinated biphenyls) and PCPs (pentachlorophenols) contaminated with dioxins were used in industry (biphenyls as insulating and heat-conducting oils in the electrical and electronics industry, chlorophenols as anti-mould agents in paints and as wood preservatives) and subsequently dispersed into the environment.
As a result, dioxins can today be detected anywhere in the environment, in the fatty tissue of animals and in woodland soil. This is due to their high chemical stability and to the large quantities of contaminated chemical products used in the recent past. The problem of dioxin in the environment is highly complex, and the scientific debate remains open. Be that as it may, human negligence and carelessness are the sole causes of the high dioxin concentrations found near old or poorly functioning incinerators, as well as around industrial complexes lacking prevention measures or effluent treatment systems (incinerators, paper mills, foundries, refineries, plastics synthesis plants) or, as in the cases a few years ago of milk seizures in the Caserta area, the result of repeated illegal waste disposal and waste burning activities.
In 1998, Europe was shaken by the Belgian dioxin-chicken scandal. The immediate response of the European Union's Veterinary Committee was to double, from 100 to 200 nanograms, the permitted quantity of PCBs in beef and pork (PCBs are linked to dioxin, which was responsible in Belgium for the animal feed scandal); the 200-nanogram limit (one nanogram is one billionth of a gram) is to be measured per gram of fat. The decision by the EU veterinary body conflicts with the opinion of the EU's Scientific Committee on Food, which had set 100 nanograms as the non-exceedable threshold for PCBs in foodstuffs — the same value provided for under Italian legislation; for this reason Italy voted against the "veterinarians'" measure, called for its immediate revision, but cannot prevent meat with double the PCB content from being imported and sold in the country. However, on 30 November 2001 the Council of the European Union adopted new limits on the dioxin content of food intended for human consumption. The new limits are significantly more restrictive.
The gradual elimination of persistent, toxic and bioaccumulative pollutants from the environment has already been addressed in various international forums. At the third International Conference on the North Sea (1990), agreement was reached on the need to reduce emissions of dioxins and other compounds by 70% or more; in 1992 the members of the Paris Convention recognised the need to gradually phase out those persistent, bioaccumulative toxic substances originating from land-based sources; the Barcelona Convention (1993) recommended the gradual cessation by 2005 of discharges into the Mediterranean Sea of organohalogen compounds from land-based sources; the International Joint Commission on the Great Lakes (IJC) urged the United States and Canada to begin a gradual phase-out of chlorine and chlorinated compounds from industrial processes (IJC 1992, IJC 1994). In December 2000, Johannesburg, delegates from one hundred nations met to ban the most dangerous and persistent pollutants, the POPs (Persistent Organic Pollutants), from DDT to dioxins and PCBs. The Stockholm Convention was drawn up in 2001 to ban 12 POPs, and entered into force in 2004.