The small chemical plant owned by Hoffmann-La Roche subsidiary ICMESA near Meda, 15 km (10 mi) north of Milan, was not considered by the locals to pose any threat, perhaps because it had been operating for many years without serious incident. But that changed in July 1976. Building B housed a complex chemical reaction producing 2,4,5-trichlorophenol, used as an intermediate for hexachlorophene and a herbicide. On July 10 operations were being shut down ahead of the weekend, when Italian law prohibited production. Unfortunately, a runaway reaction forced a relief valve to open, releasing six tons of wind-borne material that swiftly spread over an area of 18 sq km (7 sq mi).
Contained within this toxic emission was just 1 kg (2.2 lb) of – wait for it – 2,3,7,8-etrachlorodibenzodioxin (shortened for obvious reasons of convenience to TCDD or simply ‘dioxin’). This potent compound gained notoriety as a constituent of Agent Orange, a lethal herbicide used by the Americans in the Vietnam War, and even such a relatively small quantity exposed local people to an amount that was fully 100 times more concentrated than the acceptable trace amount of one part per million.
Animals died, soil was contaminated and some 37,000 people suffered varying degrees of exposure to TCDD. Many – especially children – developed skin lesions and several pregnant women chose to have abortions, only permitted in Italy under such extraordinary circumstances. The event became known as the Seveso Disaster after the town that suffered most. Two senior executives of ICMESA – technical director Herwig von Zwehl and production director Paolo Paoletti – were arrested and the Italian government mounted a massive long-term clean-up operation. As a result of this disastrous dioxin leak, the set of regulations drafted to govern industrial safety in the entire European Community is known as the Seveso II Directive.
When: July 10 1976
Where: Meda, near Seveso, Lombardy, Italy
Death toll: Around 3,300 domestic animals (including poultry) perished within days and another 80,000 were slaughtered to prevent them entering the food chain. As no people died as an immediate result of the spill, a human total is harder to estimate but there is no doubt that adverse long-term health effects contributed to a large number of early deaths – notably from respiratory and heart diseases.
You should know: ln February 1980 ICMESA’s production boss Paolo Paoletti was assassinated by a member of the radical Marxist-Leninist Italian terrorist group Prima Unea (Front Line) as part of a violent campaign against uncaring capitalism.
