Seveso dioxin release poisoned a town — and became the EU's safety law

On 10 July 1976, a runaway chemical reaction at the ICMESA plant in Meda, Italy, blew a reactor relief valve open. A white cloud of sodium hydroxide, ethylene glycol, and 15 to 30 kg of TCDD dioxin — one of the most toxic substances known — settled over 18 km² around the town of Seveso. The batch had been stopped early to comply with a mandatory weekend shutdown, but with the stirrer off and exhaust steam temperature rising undetected to 300°C, the reactor overheated past the critical threshold of 180°C and the reaction ran away.

The company initially denied a dioxin release. Evacuation began only 15 days later, when 753 residents of the most contaminated zone were moved out. Within weeks, 3,300 animals were dead and 80,000 more were culled to keep dioxin out of the food chain. Nearly 200 residents developed chloracne, the painful skin disease caused by dioxin exposure. Long-term studies later found excess deaths from lymphatic and hematopoietic cancers, particularly among women.

ICMESA and its parent Givaudan (owned by Hoffmann-La Roche) paid 20 billion lire in compensation. Five managers were convicted in 1983 with sentences of 2.5 to 5 years. The trial was a spectacle: production director Paolo Paoletti was shot dead by a terrorist group in 1980 before sentencing. The disaster led the European Community to enact the Seveso Directive in 1982, the first comprehensive EU law on major industrial hazards, which remains in force today as the Seveso III Directive.