Seveso, Italy

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Seveso, Italy

Accidents in which large quantities of dangerous chemicals are released into the environment are almost inevitable in the modern world. Toxic chemicals are produced in such large volumes today that it would be a surprise if such accidents were never to occur. One of the most infamous accidents of this kind occurred at Seveso, Italy, a town near Milan, on July 10, 1976.

The Swiss manufacturing firm of Hoffman-LaRoche operated a plant at Seveso for the production of hexachlorophene, a widely used disinfectant. One of the raw materials used in this process is 2,4,5-trichlorophenol (2,4,5-TCP). At one point in the operation, a vessel containing 2,4,5-TCP exploded, releasing the chemical into the atmosphere . A cloud 100160 ft (3050 m) high escaped from the plant and then drifted downwind. It eventually covered an area about 2,300 ft (700 m) wide and 1.2 m (2 km) long.

Although 2,4,5-TCP is a skin irritant, it was not this chemical that caused concern. Instead, it was an impurity in 2,4,5-TCP, a compound called 2,3,7,8-tetrachlorodi-benzo-p-dioxin, that caused alarm. This compound, one of a family known as dioxins, is one the most toxic chemicals known to science. It occurs as a by-product in many manufacturing reactions in which 2,4,5-TCP is involved. Experts estimated that 735 lb (316 kg) of dioxin were released into the atmosphere as a result of the Seveso explosion.

People living closest to the Hoffman-LaRoche plant were evacuated from their homes and the area was closed off. About 5,000 nearby residents were allowed to stay, but were prohibited from raising crops or farm animals.

Damage to plants and animals in the exposed area was severe. Thousands of farm animals died or had to be destroyed. More than 2.5 tons (225 kg) of contaminated soil were removed before planting could begin again. Short- and long-term effects on human health, however, were relatively modest. In the months following the accident, 176 individuals were found to have chloracne, an inflammation of the skin caused by chlorine-based chemicals. An additional 137 cases of the condition were found in a follow-up survey six months after the accident.

Other health problems were also detected in the human population. About 8% of the exposed population had enlarged livers and a few residents showed signs of minor nerve damage. Some people claimed that exposed women had higher rates of miscarriage and of deformed children, but local authorities were unable to substantiate these claims. No human lives were lost in the accident.

[David E. Newton ]



Harrison, R. M., ed. Pollution: Causes, Effects, and Control. Cambridge, Royal Society of Chemistry, 1990.


Walsh, J. "Seveso: The Questions Persist Where Dioxin Created a Wasteland." Science (September 9, 1977): 10641067.

. "Reporter at Large: Dioxin Pollution of Seveso." New Yorker (September 4, 1978): 3436+.

Whiteside, T. "Reporter at Large: TCDD Explosion at Icmesa Chemical Plant." New Yorker (July 25, 1977): 41+.