Seveso, Italy


Accidents in which large quantities of dangerous chemicals are released into the environment are seemingly inevitable in the modern world. In fact, toxic chemicals are produced in such large volumes today that it would be a surprise if such accidents never occurred. One of the most infamous accidents of this kind occurred at Seveso, Italy, a town near Milan in the Lombardy region in Italy, on July 10, 1976. This industrial accident resulted in the exposure of its residents to 2,3,7,8-tetrachlorodibenzo-pdioxin (TCDD), an ingredient within the chemical commonly known as dioxin, a poisonous and carcinogenic substance.


Hoffman-LaRoche, a small Swiss chemical manufacturing firm, operated a plant at Seveso for the production of hexachlorophene, a widely used disinfectant, for use in pesticides and herbicides. Specifically, the company ICMESA (Industrie Chimiche Meda Societá Azionaria), a subsidiary of Givaudan, owned the plant, which was itself a subsidiary of Hoffmann-La Roche (Roche Group). One of the raw materials used in this process is 2,4,5-trichlorophenol (2,4,5-TCP). At one point in the operation—at approximately 12:37 p.m. local time on July 10, 1976—a vessel containing 2,4,5-TCP exploded, releasing the carcinogenic chemical into the atmosphere as a toxic vapor. A cloud 100–160 feet (30–50 meters) high escaped from the plant and then drifted downwind. It eventually covered an area about 2,300 feet (700 meters) wide and 1.2 miles (2 kilometers) long.

The area most affected by the chemical exposure—the one that contained the highest concentration of contaminated soil—contained over 700 residents. Further out, an area with a lower soil contamination concentration contained about 4,700 residents, and still further out with an even lower concentration of contaminated soil was a population of about 31,800. Following the accident, several thousand farm and wild animals died. The rest of the farm animals were slaughtered to prevent their meat from entering the food chain. Fifteen children were hospitalized with skin inflammation. Just over 400 adults were also found to have skin lesions.

Risk factors

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, the compound 2,3,7,8-tetrachlorodibenzo-p-dioxin, that caused alarm. This compound, one of a family known as dioxins, is one of the most toxic chemicals known to science. It occurs as a byproduct in many manufacturing reactions in which 2,4,5-TCP is involved, especially when the reaction temperature is high. Experts estimated that 7–35 pounds (3–16 kilograms) of dioxin were released into the atmosphere as a result of the Seveso explosion.


In addition to the city of Severso, which had a population of about 17,000 residents at the time of the disaster, other nearby communities were affected. These included Barlassina (with a population of about 6,000), Bovisio-Masciago (11,000), Cesano Maderno (34,000), Desio (33,000), and Meda (19,000).

Although exposures to dioxins had occurred in the past, they were minor occurrences. This one was a major event, one that warranted evacuating residents. 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 subsequently prohibited from raising crops or farm animals.

Causes and symptoms

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 kilograms) of contaminated soil were removed before planting could begin again. Short- and long-term effects on human health, however, were relatively modest.

Common diseases and disorders

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.

Cancer causing.
A skin rash that resembles acne, which is caused by repeated contact with chlorinated hydrocarbons.
Any of numerous by-products of various industrial processes, which are regarded as extremely toxic. These dioxins or dioxin-like compounds include polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and polychlorinated biphenyls (PCBs).

Some people claimed that exposed women had higher rates of miscarriage and of deformed babies, but local authorities were unable to substantiate these claims. No human lives were lost in the accident.


Over 600 people were evacuated from their residences as the result of being exposed to dioxin at Seveso, and upwards of 2,000 people were treated for dioxin poisoning.

Public health role and response

Within six months of the accident, a plan to decontaminate and restore the affected area had been completed. That plan was implemented in the spring of 1977. By June 1977, over 200,000 people were being monitored for adverse health effects from the incident. An international team, including biostatisticians, epidemiologists, toxicologists and pathologists, from the International Steering Committee began a scientific assessment of the situation. With its 1983 report The Work of the International Steering Committee for the Study of the Health Effects of the Seveso Accident: Its Methodology, Its Issues and Its Conclusions, the committee concluded that no human effects other than 193 cases of chloracne occurred within the Seveso disaster.


The Seveso chemical exposure incident is increasingly seen as a lucky escape, where a potentially catastrophic release caused relatively little damage.


See also Cancer ; Chemical poisoning ; Dioxins .



Hites, Ronald A., and Jonathan D. Raff. Elements of Environmental Chemistry. Hoboken, NJ: Wiley and Sons, 2012.

Schecter, Arnold, ed. Dioxins and Health: Including Other Persistent Organic Pollutants and Endocrine Disruptors. Hoboken, NJ: John Wiley and Sons, 2012.

Spiro, Thomas G, Kathleen L. Purvis-Roberts, and William M. Stigliani. Chemistry of the Environment. Mill Valley, CA: University Science Books, 2012.


Center for Environmental Research and Children's Health. “Seveso Women's Health Study.” (accessed September 20, 2012).

European Commission. “Chemical Accidents (Seveso III)—Prevention, Preparedness and Response.” (accessed September 20, 2012).


American Association of Poison Control Centers, (800) 222-1222, .

Center for Environmental Research and Children's Health (University of California at Berkeley), 1995 University Ave., Ste. 265, Berkeley, CA, 94720-7392, (510) 643-9598, Fax: (510) 642-9083,, .

National Toxicology Program (National Institute of Environmental Health Sciences), PO Box 12233, Research Triangle Park, NC, 27709, .

World Health Organization, Avenue Appia 20, Geneva, Switzerland, 1211 27, 41 22 791-2111, Fax: 41 22 791-3111,, .

David E. Newton, EdD
Revised by William A. Atkins, B.B., B.S., M.B.A.

  This information is not a tool for self-diagnosis or a substitute for professional care.