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Seveso disaster

The Seveso disaster was an industrial accident that occurred around 12:37 pm on July 10, 1976, in a small chemical manufacturing plant approximately 15 kilometres (9 mi) north of Milan in the Lombardy region of Italy. It resulted in the highest known exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) 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.


  • Location 1
  • Chemical events 2
  • Immediate effects 3
  • Studies on immediate and long-term health effects 4
  • Cleanup operations 5
    • Waste from the cleanup 5.1
    • Criminal court case 5.2
  • Conclusions 6
  • References 7
  • Further reading 8
  • External links 9


The Seveso disaster was named because Seveso, with a population of 17,000 in 1976, was the community most affected. Other affected neighbouring communities were Meda (19,000), Desio (33,000), Cesano Maderno (34,000) and to a lesser extent Barlassina (6,000) and Bovisio-Masciago (11,000).[2] The industrial plant, located in Meda, was owned by the company ICMESA (Industrie Chimiche Meda Società Azionaria), a subsidiary of Givaudan, which in turn was a subsidiary of Hoffmann-La Roche (Roche Group). The factory building had been built many years earlier and the local population did not perceive it as a potential source of danger. Moreover, although several exposures of populations to dioxins had occurred before; mostly in industrial accidents, they were of a more limited scale.

Chemical events

Overall Reaction scheme

The accident occurred in the chemical plant's building B. The chemical 2,4,5-trichlorophenol (2) was being produced there from 1,2,4,5-tetrachlorobenzene (1) by the nucleophilic aromatic substitution reaction with sodium hydroxide. The 2,4,5-trichlorophenol was intended as an intermediate for hexachlorophene,[3] although it can also be used as an intermediate for the herbicide 2,4,5-T (2,4,5-trichlorophenoxyacetic acid).

This reaction must be carried out at a temperature above what was achievable using the normal process utilities available at the plant, so it was decided to use the exhaust steam from the onsite electricity generation turbine, and pass that around an external heating coil installed on the chemical reactor vessel. The exhaust steam pressure was normally 12 bar and temperature 190 °C, which resulted in a reaction mixture temperature of 158 °C, very close to its boiling point of 160 °C. Safety testing showed the onset of an exothermic side reaction if the reaction mixture temperature reached 230 °C. Crucially, no steam temperature reading was made available to plant operators responsible for the reactor.

The chemical-release accident occurred when a batch process was interrupted prior to the completion of the final step – removal of ethylene glycol from the reaction mixture by distillation, due to conformance with an Italian law requiring shutdown of plant operations over the weekend. Other parts of the site had already started to close down as the processing of other batches finished, which reduced power consumption across the plant, causing a dramatic drop in the load on the turbine and a consequent increase in the temperature of the exhaust steam to around 300 °C. This much hotter steam then proceeded to heat the portion of the metal wall of the accident reactor above the level of the liquid within it to the same temperature. Not having a steam temperature reading among their instruments, operators of the reactor were unaware of the presence of this additional heating, and they stopped the batch as they normally would – by isolating the steam and turning off the stirrer in the reactor vessel. The abnormally-hot upper region of the reactor jacket then heated the adjacent reaction mixture. With the stirrer not running, the heating was highly localised – confined to just the portion of the upper layers of reaction mixture adjacent to the reactor wall, and increased the local temperature to the critical temperature for the exothermic side reaction seen in testing. Indeed, the critical temperature proved to be only 180 °C, 50 °C lower than believed. At that lower critical temperature, a slow runaway decomposition began, releasing more heat and leading to the onset of a rapid runaway reaction when the temperature reached 230 °C seven hours later.[4][5]

The reactor relief valve eventually opened, causing the aerial release of 6 tonnes of chemicals, which settled over 18 km2 (6.9 sq mi) of the surrounding area.[6] Among the substances released was 1 kg of 2,3,7,8-tetrachlorodibenzodioxin (TCDD) (3). At the nominal reaction temperature, TCDD is normally seen only in trace amounts of less than 1 ppm (parts per million).[7] However, in the higher-temperature conditions associated with the runaway reaction, TCDD production apparently reached 100 ppm or more.[8]

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 per square metre (µg/m²), it had 736 residents.
  • Zone B had a TCDD soil concentration of between 5 and 50 µg/m², it had about 4700 residents.
  • Zone R had negligible or a TCDD soil concentration of < 5 µg/m², it had 31,800 residents.

Within days a total of 3,300 animals were found dead, mostly poultry and rabbits. Emergency slaughtering commenced to prevent TCDD from entering the food chain, and 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, 1,600 people of all ages had been examined and 447 were found to suffer from skin lesions or chloracne. An advice center was set up for pregnant women of which only 26 opted for an abortion, which was legal in special cases, after consultation. Another 460 women brought on their pregnancies without problems, their children not showing any sign of malformation or pathologies. Herwig von Zwehl (Technical Director of ICMESA) and Paolo Paoletti (director of production at ICMESA) were arrested. Two government commissions were established to develop a plan for quarantining and decontaminating the area, for which the Italian government allotted 40 billion lire (US $47.8 million). This amount would be tripled two years later.

Studies on immediate and long-term health effects

A 1991 study[9] 14 years after the accident sought to assess the effects to the thousands of persons that had been exposed to dioxin. The most evident adverse health effect ascertained was chloracne (193 cases). Other early effects noted were peripheral neuropathy and liver enzyme induction. The ascertainment of other, possibly severe sequelae of dioxin exposure (e.g., birth defects) was hampered by inadequate information; however, generally, no increased risks were evident.

A study published in 1998 concluded that chloracne (nearly 200 cases with a definite exposure dependence) was the only effect established with certainty. Early health investigations including liver function, immune function, neurologic impairment, and reproductive effects yielded inconclusive results.

An excess mortality from cardiovascular and respiratory diseases was uncovered, and excess of diabetes cases was also found. Results of cancer incidence and mortality follow-up showed an increased occurrence of cancer of the gastrointestinal sites and of the lymphatic and hematopoietic tissue. Results cannot be viewed as final or comprehensive, however, because of various limitations: the lack of individual exposure data, short latency period, and small population size for certain cancer types.

A 2001 study[10] confirmed in victims of the disaster, that dioxin is carcinogenic to humans and corroborate its association with cardiovascular- and endocrine-related effects. In 2009, an update including 5 more years (up to 1996) found an increase in "lymphatic and hematopoietic tissue neoplasms" and increased breast cancer.[11]

Cleanup operations

In January 1977, an action plan consisting 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. They then used trichlorophenol to make a drug to fight the skin infections, which they tested in dogs.

In June 1978, the Italian government raised its special loan from 40 to 115 billion lire. By the end of the year most individual compensation claims had been settled Prima Linea.[12] On December 19, 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 lire.

Waste from the cleanup

The waste from the clean up of the plant was a mixture of protective clothing and chemical residues from the plant. This waste was packed into waste drums which had been designed for the storage of nuclear waste. It was agreed that the waste would be disposed of in a legal manner.

To this end, 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 September 9, 41 barrels of toxic waste left the ICMESA premises. On December 13, the notary gave a sworn statement that the barrels had been disposed of in an approved way.

However, in February 1983, the programme "A bon entendeur" on Télévision Suisse Romande, a French language Swiss TV channel, followed the route of the barrels to Saint-Quentin in northern France where they disappeared. A public debate ensued in which numerous theories were put forward when it was found that Mannesmann Italiana had hired two subcontractors to get rid of the toxic waste. On May 19 the 41 barrels were found in an unused abattoir (slaughterhouse) 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 upon itself to properly dispose of the waste. On November 25, 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. According to New Scientist it was thought that the high chlorine content of the waste might cause damage to the high temperature incinerator used by Roche, but Roche stated that they would burn the waste in the incinerator and repair it afterward if it were damaged. They stated that they wanted to take responsibility for the safe destruction of the waste.

Criminal court case

In September 1983, the Criminal Court of Monza sentenced five former employees of ICMESA or its parent company, Givaudan, to prison sentences ranging from 2.5 years to 5 years. They all appealed.

In May 1985, the Court of Appeal in Milan found three of the five accused not guilty; the two still facing prosecution appealed to the Supreme Court in Rome.

On May 23, 1986, the Supreme Court in Rome confirmed the judgment against the two remaining defendants, even though the prosecuting attorney had called for their acquittal.


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 unaware when the accident happened and unprepared to cope with the danger of an invisible poison.

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, 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."[13]

Industrial safety regulations were passed in the European Community in 1982 called the Seveso Directive[14] which imposed much harsher industrial regulations. The Seveso Directive was updated in 1996, amended lastly in 2008 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.

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. 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 statistically significant excess has yet been observed.

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).

The Seveso disaster gives valuable comparative insight into the effects of Agent Orange on flora and fauna in Vietnam, not to mention the Vietnamese people, as TCDD was a significant contaminant in Agent Orange.[15]

The documentary Gambit is about Joerg Sambeth, the technical director of ICMESA, who was sentenced to five years in the first trial, and had his sentence reduced to two years and was paroled on appeal.[16]


  1. ^ Brenda Eskenazi; Paolo Mocarelli, Marcella Warner, Larry Needham, Donald G. Patterson, Jr., Steven Samuels, Wayman Turner, Pier Mario Gerthoux, and Paolo Brambilla (January 2004). "Relationship of Serum TCDD Concentrations and Age at Exposure of Female Residents of Seveso, Italy". Environmental Health Perspectives 112 (1): 22–7.  
  2. ^ B. De Marchi; S. Funtowicz; J. Ravetz. "4 Seveso: A paradoxical classic disaster".  
  3. ^ Homberger, E.; Reggiani, G.; Sambeth, J.; Wipf, H. K. (1979). "The Seveso Accident: Its Nature, Extent and Consequences". Ann. Occup. Hyg ( 
  4. ^ T. Kletz What Went Wrong? Case Histories of Process Plant Disasters(1998) Gulf, ISBN 0-88415-920-5;
  5. ^  
  6. ^ [2]
  7. ^ Milnes, M. H. (6 August 1971). "Formation of 2,3,7,8-Tetrachlorodibenzodioxin by Thermal Decomposition of Sodium 2,4,5-Trichlorophenate".  
  8. ^ Hay, Alastair (18 October 1979). "Séveso: the crucial question of reactor safety".  
  9. ^ Bertazzi, Pier Alberto (1991). "Long-term effects of chemical disasters. Lessons and results from Seveso". The Science of the Total Environment 106 (1-2): 5–20.  
  10. ^ Bertazzi, Pier Alberto; Consonni, Dario; Bachetti, Silvia; Rubagotti, Maurizia; Baccarelli, Andrea; Zocchetti, Carlo; Pesatori, Angela C. (June 1, 2001). "Health Effects of Dioxin Exposure: A 20-Year Mortality Study.". American Journal of Epidemiology 153 (11): 1031–1044.  
  11. ^ Pesatori, A.; Consonni, D.; Rubagotti, M.; Grillo, P.; Bertazzi, P. (2009). "Cancer incidence in the population exposed to dioxin after the "Seveso accident": twenty years of follow-up". Environmental health : a global access science source 8 (1): 39.  Free full-text
  12. ^ . 
  13. ^ B. De Marchi; S. Funtowicz; J. Ravetz. "Conclusion: "Seveso" - A paradoxical symbol". United Nations University. 
  14. ^ "Original Seveso Directive 82/501/EEC ("Seveso I")" (pdf). 
  15. ^ "Vietnam Agent Orange Campaign - Background". 
  16. ^ "Ich war absolut dumm" (in German). 

Further reading

  • Fuller, John G. (1979). Poison That Fell from the Sky. New York: Berkley Books.  

External links

  • Loss Prevention Bulletin The Seveso Disaster: An appraisal of its causes and circumstances, Marshall, V.C., LPB Issue 104, April 1992, IChemE, UK
  • 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. July 9, 1976 British Health & Safety Executive COMAH information page on the Seveso Disaster.
  • Assessment of the Health Risks of Dioxins, a 1998 report by the World Health Organisation.
  • Roche - 1965 - 1978 pdf History timeline at the homepage of Hoffmann-LaRoche.

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