Thursday, January 24, 2013

Seveso Disaster : the Dioxin Crisis

ICMESA plant after the accident

Summary data 

Date : July 10th 1976
Place : the ICMESA factory at Meda near Milan, Italy
Type of accident : dioxin release
Outcome : 725 people evacuated, 2000 people treated for dioxin poisoning, 4% of the local farm animals dead and 80 000 additional animals killed to prevent contamination from filtering up the food chain.

Overview of the accident

We are in the chemical plant ICMESA owned by the Swiss company Givaudan (group Hoggmann-Laroche), located in Meda, a small town about 20 kilometres north of Milan.
On Saturday 10th July 1976, the control system of a chemical reactor for the production of trichlorophenol, a component of several herbicides, was damaged, and the temperature rose beyond the limits. The explosion of the reactor was avoided by the opening of safety valves, but the high temperature reached had caused a change in the reaction that led to a massive formation of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), substance commonly known as dioxin, a high toxic compound.

This event became internationally known as the Seveso disaster since Seveso is the name of a neighbouring municipality that was the most severely affected.
After four days, Hoffmann-La Roche laboratories identified the causative agent (TCDD). By Thursday 15 July, five days after the accident, ICMESA had informed the authorities of the presence of toxic components while the population continued to live in a contaminated environment.
Zone A represents the area with the highest level of 
dioxin contamination, followed by Zone B and Zone R
The evacuation was ordered on Saturday 24 July, two weeks after the accident. On July 26, the first inhabitants were evacuated and 225 people left their homes. During the days that followed days, the authorities realized that the affected area was larger and 500 more people were evacuated.
The dioxin cloud, released into the air from the chemical plant, contaminated a densely populated area. The four most impacted municipalities were Seveso (a 1976 population of 17 000), Meda (19 000), Desio (33 000), and Cesano Maderno (34 000). Two other municipalities, Barlassina (6000) and Bovisio Masciago (11 000) were subject to post accident restrictions.

 The amount of TCDD released by the accident is subject to much debate. It is possible that between 1 and 30 kg of dioxin was release in the atmosphere.

The Seveso disaster areas were divided based on soil contamination levels. Zone A, the most contaminated area with more than 50 mg of TCDD per square meter and covering 110 ha, was completely evacuated and fenced-off with entry prohibited.
In the next-most contaminated areas, zone B (between 5 and 50 mg/m2) and zone R (below 5 mg/m2), farming as well as consumption of local agricultural goods and meats were strictly prohibited.

Consequences of the accident

A child diagnosed with chloracne
In the days following the accident, the trees turned yellow and dropped their leaves and thousands of pets died. In order to prevent TCDD from entering the food chain over 80 000 animals had to be slaughtered.
15 children were quickly hospitalized with skin inflammation. 1 600 people of all ages had been examined and 447 were found to suffer from skin lesions or chloracne. Pregnant women who wanted an abortion had been allowed to, which was usually unthinkable in Catholic Italy at that time.
The release of dioxin has not resulted in deaths. However, the plant manager, Paolo Paoletti, was assassinated shortly after by an armed group.

Lessons from the accident

The best-known consequence of the Seveso disaster was the creation of the European Community's Seveso Directive, a new system of industrial regulation.
The new European directives, Seveso I and II, were then used to identify sites at risk of major accidents and to establish a policy to prevent major accidents.
The resulting directives are currently applied to around 10 000 industrial establishments where dangerous substances are used or stored in large quantities, mainly in the chemicals, petrochemicals, storage, and refining sectors.
The industries handling dangerous substances above certain thresholds must regularly inform the public, providing safety reports, a safety management system and an internal emergency plan.

Sources :
- Lessons from seveso, David C. Wilson, Chemistry in Britain, July 1982, available at :
- Case Study: The Dioxin Crisis in Seveso, Italy, available at :
- 4 Seveso: A paradoxical classic disaster, B. De Marchi, S. Funtowicz, and J. Ravetz, United Nations University, available at :
- Seveso Dioxin Cloud, Gilbert Cruz, TIME, May 2010, available at :,28804,1986457_1986501_1986449,00.html
- Que s’est-il passé à Seveso ?, Matthieu Combe, April 2012, available :
- Chemical Accidents (Seveso III) - Prevention, Preparedness and Response, European Comission , November 2012, available at :


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