The Seveso disaster was an industrial accident that occurred around 12:37 pm July 10, 1976 in a small chemical manufacturing plant approximately 25 km north of Milan in the Lombardy region in Italy. It resulted in the highest known exposure to TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) in residential populations 1 which gave rise to numerous scientific studies and standardized industrial safety regulations. The EU industrial safety regulations are known as the Seveso II Directive.

Many things about the exact circumstances of the accident are unknown and perhaps irrelevant. Fortunately the Seveso disaster was a serious industrial accident that did not have grave consequences, there were no fatalities. Nevertheless TCDD is a known carcinogen and one of the most toxic substance on earth. The accident exposed serious flaws in government response to industrial accidents. No human is known to have died from dioxin poisoning but its toxic effects have been documented in cases such as the Yusho disaster in Japan in 1968, the Yucheng disaster in Taivan in 19792 as well as in Viet Nam War veterans who processed and sprayed Agent Orange. Most recently Viktor Yushchenko, the president of Ukraine, was poisoned with TCDD and subsequently suffered from chloracne.


Dioxins are a group of persistant organic pollutants, they do not react easily with other chemicals, that is to say they are lipophilic, they bioaccumulate. Some of them are extremely toxic and fatal when it comes to animal studies but scientific evidence of harmfulness to humans is disputed. A subgroup of polychlorinated dibenzo-p-dioxins (PCDDs) are amongst the most toxic. The number and position of the chlorine atoms determine the toxicity of the PCDD and the most toxic among them is 2,3,7,8-tetrachlorodibenzo-p-dioxin (commonly referred to as "dioxin").

In humans and other vertebrates dioxins have been shown to be risk factors for cancer; immune deficiency; reproductive and developmental abnormalities; central nervous system and peripheral nervous system pathology; endocrine disruption, including diabetes and thyroid disorders; decreased pulmonary functions and bronchitis; altered serum testosterone level; eyelid pathology, including meibomian gland hypersecretion and hyperpigmented conjunctivae; gum pigmentation; nausea; vomiting; loss of appetite; skin rashes, including, rarely, chloracne or acne caused by chlorine-containing organic chemicals; hypertrichosis; liver damage; elevated serum cholesterol and triglycerides; and enamel hypomineralization of permanent first molars in children. An increased risk of mortality was associated with high levels of occupational exposure to dioxins with acute ischemic cardiovascular events. Transient acute health effects including headache, pruritis, fatigue, irritability, inability to have erections or ejaculations, personality changes, pain in the abdomen or extremities, diarrhea, and insomnia have been reported, especially following industrial exposures.3

The accident

The Seveso disaster was so named because Seveso was the community most affected. Seveso is a small town with the population of 17,000 in 1976, other affected neighbourhood communities were Meda (19,000), Desio (33,000), Caesano Maderno (34,000) and to a lesser extent Barlassina (6,000) and Bovisio Masciago (11,000)4. The industrial plant was close by Meda, owned by the company ICMESA (Industrie Chimiche Meda Società), a subsidiary of Givaudan which in turn was a subsidiary of Hoffmann-La Roche (Roche Group). The factory building was built many years ago and the local population did not perceive it as a potential source of danger. Moreover although several industrial accidents involving dioxins had occured before they were of a more limited scale with the exception of the use of Agent Orange as a chemical weapon during the Viet Nam War.

The accident occured in building B where 2,4,5-trichlorophenol (TCP), a herbicide, was being produced later to be used as an intermediate in the production of hexachlorophene, a medical disinfectant. An unintended byproduct of the manufacture of TCP is TCDD in trace amounts, measured in ppm (parts per million). Due to human error, around mid-noon on a Saturday, an uncontrolled reaction occurred bursting the security disk of the chemical reactor and an aerosol cloud containing sodium hydroxide, ethylene glycol, sodium trichlorophenate, and somewhere between a few hundred grams and up to a few kgs of TCDD was released over an 18 km² area.

Immediate effects

The affected area was split into zones A, B and R in decreasing order of surface soil concentrations of TCDD. Zone A was further split into 7 sub-zones. The local population was advised not to touch or eat locally grown fruits or vegetables.

    Zone A had a TCDD soil concentration of > 50 micrograms/m², it had 736 residents.

    Zone B had a TCDD soil concentration of between 5-50 micrograms/m², it had about 4700 residents.

    Zone R had neglible or a TCDD soil concentration of < 5 micrograms/m², it had 31,800 residents.

Within days a total of 3300 animals were found dead, mostly poultry and rabbits. Emergency slaughtering commensed to prevent TCDD from entering the food chain, by 1978 over 80,000 animals had been slaughtered. 15 children were quickly hospitalised with skin inflammation. By the end of August Zone A had been completely evacuated and fenced, 1600 people of all ages had been examined and 447 were found to suffer from skin lesions or chloracne. An advice center was been set up for pregnant women of which several opted for an abortion, which was legal in special cases, after consultation. Herwig von Zwehl the Technical Director of Icmesa and Dr. Paolo Paoletti, director of production at Icmesa were arrested. Then two government commissions were established to thrash out a plan for quarantining and decontaminating the area and finally the Italian government diverted 40 billion liras from its coffers, this amount would be tripled two years later.

Cleanup operations

In January 1977 an action plan compromised of scientific analysis, economic aid, medical monitoring and restoration/decontamination was completed. Shortly after Icmesa began to pay the first compensations to those affected. Later that spring decontamination operations were initiated and in June a system epidemiological health monitoring for 220,000 people was launched. In September The International Steering Committee was created, staffed with "renowned experts from all over the world", in order to assess the scientific data generated.

In June 1978 the Italian government raised its special loan from 40 to 115 billion liras. By the end of the year most individual compensation claims had been settled out of court. On the 2nd February 1980 Paolo Paoletti, the Director of Production at Icmesa was shot and killed in Monza by a member of the Italian radical left-wing terrorist organization Prima Linea. On the 19th of December 1980 representatives of the Region of Lombardy/Italian Republic and Givaudan/Icmesa signed a compensation agreement in the presence of the prime minister of Italy, Arnaldo Forlani. The total amount would reach 20 billion liras.

In spring 1982 the firm Mannesmann Italiana was contracted to dispose of the contaminated chemicals from Zone A. Mannesmann Italiana made it a condition that Givaudan would not be notified of the disposal site which prompted Givaudan to insist that a notary public certify the disposal. On the 9th of September 41 barrels of toxic waste left the Icmesa premises. On the 13th of December, the notary gave a sworn statement that the barrels had been disposed of in an approved way.

However in February 1983 a French/Swiss television programme followed the route of the barrels to St-Quentin in northern France where they disappeared. A public debate ensued in which numerous theories were put forward when it was found out that Mannesmann Italiana hired two subcontractors to get rid of the toxic waste. On the 19th of May the 41 barrels were found in an unused abattoir in Anguilcourt-le-Sart, a village in northern France. From there they were transferred to a French military base near Sissonne. The Roche Group (parent firm of Givaudan) took it unto itself to properly dispose of the waste. In September the Criminal Court of Monza sentenced five former employees of Icmesa to prison sentences ranging from 2½ years to 5 years. They all appealed.

In February, 1984 The International Steering Committee released its final report stating that "with the exception of chloracne, no ill effects can be attributed to TCDD".

In May 1985 the Court of Appeal in Milan finds three of the five accused not guilty, the two still facing prosecution appealed to the Supreme Court in Rome. On the 25th of November, over nine years after the disaster, the Roche Group issued a public statement that the toxic waste consisting of 42 barrels (1 was added earlier that year) had all been incinerated in Switzerland.

On the 23rd of May 1986 the Supreme Court in Rome confirmed the judgment against the two remaining even though the prosecuting attorney had called for their aquittal.


The safety operations handled by the company's directors and local government were badly coordinated and to some extent incompetent. At least a week passed before it was publicly stated that dioxin had been emitted and another week passed before evacuation began. Few scientific studies had confirmed the level of danger TCDD posed and there were scant industrial regulations to be followed. As a result the local population was caught unawares when the accident happened and in such an insecure situation became very frightened. Confrontation with an invisible poison possibly extremely hazardous to human health was a very traumatic experience for small rural communities.

"In the context of such heightened tensions, Seveso became a microcosm where all the existing conflicts within society (political, institutional, religious, industrial) were reflected. However, within a relatively short time such conflicts abated and the recovery of the community proceeded. For, in Seveso, blame was never at issue: the responsible party was known from the outset and soon offered reparation. Moreover, the eventual disappearance of the offending factory itself and the physical exportation of the toxic substances and polluted soil enabled the community to feel cleansed. The resolution of the emotional after-effects of the trauma, so necessary for the recovery of a community, was facilitated by these favourable circumstances."5

Industrial safety regulations were passed in the European Community in 1982 called the Seveso Directive which imposed much harsher industrial regulations. The Seveso Directive was updated in 1999, amended again in 2005 and is currently referred to as the Seveso II Directive (or COMAH Regulations in the United Kingdom).

Treatment of the soil in the affected areas was so complete that it now has a dioxin level below what would normally be found. The whole site has been turned into a public park, Seveso Oak Forest park. Some say that Seveso is now the least polluted place in Italy.

It could be argued that Seveso is a disaster that has not yet produced identifiable disastrous consequences. Several studies have been completed on the health of the population of surrounding communities.

Epidemiological monitoring programmes established as follows (with termination dates): abortions (1982); malformations (1982); tumours (1997); deaths (1997). Health monitoring of workers at ICMESA and on decontamination projects, and chloracne sufferers (1985).

Searching with scholarly search engines such as or ProQuest it is easy to find a wide variety on dioxin related studies. The Seveso Disaster has been studied a lot. It has been established that people from Seveso exposed to TCDD are more susceptible to rare cancers but when all types of cancers are grouped into one category, no statistical significant excess has yet been observed.

The Seveso disaster gives valuable comparative insight into the effects of Agent Orange on flora and fauna in Vietnam, not to mention Vietnamese people as TCDD was the active toxic chemical in Agent Orange6.


1 - - "Relationship of Serum TCDD Concentrations and Age at Exposure of Female Residents of Seveso, Italy" Environmental Health Perspectives Volume 112, Number 1, January 2004
2 - - "Dioxin exposure threat to baby boys" - BBC 12 July, 2002.
3> - - "Dioxins: An overview" by Arnold Schecter, Linda Birnbaum, John J. Ryan and John D. Constable. Environmental Research Volume 101, Issue 3 , July 2006, Pages 419-428
4 - - "Seveso: A paradoxical classic disaster" by B. De Marchi, S. Funtowicz, and J. Ravetz, Chapter 4 of The long road to recovery: Community responses to industrial disaster published by United Nations University.
5 - - "Seveso: A paradoxical classic disaster : Conclusion" by B. De Marchi, S. Funtowicz, and J. Ravetz, Chapter 4 of The long road to recovery: Community responses to industrial disaster published by United Nations University.
6 - - Vietnam Agent Orange Campaign. Brochure.

Other references
* National Pollutant Inventory - Dioxin Fact Sheet
* Dioxin: Seveso disaster testament to effects of dioxin, article by Mick Corliss, May 6, 1999
* Icmesa chemical company, Seveso, Italy. 9th July 1976 British Health & Safety Executive COMAH information page on the Seveso Disaster
* "Assesment of the Health Risks of Dioxins", a 1998 report by the World Health Organisation.
* Roche - 1965 - 1978 History timeline at the homepage of Hoffmann-LaRoche.
* Seveseo - 30 years after a timeline of the accident running up to 2000, prepared by Hoffman-LaRoche. *

The documentary The Gambit about Jorg Sambeth, the technical director of Icmesa who was prisoned for 2 years, is available -

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