Italian Factory Explosion Releases Dioxin Summary

  • Last updated on November 10, 2022

An explosion at a factory released toxic chemicals into the atmosphere, exposing large numbers of people and contaminating the soil. The accident led to the implementation of more stringent controls on trichlorophenol manufacture in many industrialized countries.

Summary of Event

At 12:40 p.m. on July 10, 1976, six and one-half hours after a chemical plant in Seveso, a working-class suburb of Milan, Italy, had closed down for the weekend, a runaway reaction in one of its reactors produced an explosion that blew a safety valve and vented the contents into the atmosphere. The explosion released a mixture of trichlorophenol, trichlorobenzene, ethylene glycol, sodium chloride, and sodium hydroxide, but the most dangerous substance released was a contaminant and by-product of the manufacturing process, tetrachlorodibenzopara-dioxin (TCDD). Authorities later estimated on the basis of the soil contamination that between 450 grams and 3 kilograms of TCDD were spread over an area of 249 hectares, inhabited by a population of 5,904 people, of whom 1,835 were children. Tetrachlorodibenzopara-dioxin Disasters;industrial Ecological disasters Dioxins [kw]Italian Factory Explosion Releases Dioxin (July 10, 1976) [kw]Factory Explosion Releases Dioxin, Italian (July 10, 1976) [kw]Explosion Releases Dioxin, Italian Factory (July 10, 1976) [kw]Dioxin, Italian Factory Explosion Releases (July 10, 1976) Tetrachlorodibenzopara-dioxin Disasters;industrial Ecological disasters Dioxins [g]Europe;July 10, 1976: Italian Factory Explosion Releases Dioxin[02440] [g]Italy;July 10, 1976: Italian Factory Explosion Releases Dioxin[02440] [c]Disasters;July 10, 1976: Italian Factory Explosion Releases Dioxin[02440] [c]Environmental issues;July 10, 1976: Italian Factory Explosion Releases Dioxin[02440] Rocca, Francesco Waldvogel, Guy

The effects of the local population’s exposure to the toxic and potentially carcinogenic TCDD were exacerbated by the response of the company involved, Givaudan/ICMESA, a subsidiary of Hoffmann-La Roche. Representatives of the company informed local officials on July 12 that an accident had occurred, but it was not until July 26, three days after a provincial diagnostic center had turned up evidence of TCDD, that ICMESA confirmed that the explosion had released dioxin. Consequently, it was not until July 27, two and one-half weeks after the explosion, that children began to be evacuated from the contaminated area. Initially, the company had identified trichlorophenol as the worst component of the emissions, which led local authorities to believe that evacuation was unnecessary, although they did warn people not to consume crops from the area surrounding the factory.

It is unlikely that company officials were unaware of the dioxin danger, as dioxin had long been identified as a by-product of trichlorophenol manufacture and had been implicated in two previous industrial accidents, one in 1958 at Badische Anilin- und Soda-Fabrik (BASF), in Germany, and the other in 1963 at the Philips Duphar complex in Amsterdam. In both accidents, workers exposed to dioxin developed chloracne, a severe, potentially disfiguring skin condition, and symptoms of systemic poisoning. The German firm ceased production of trichlorophenol after the accident, and Philips Duphar dismantled the contaminated plant brick by brick, encasing the rubble in concrete before dumping it into the ocean. There was thus abundant evidence by 1976 that trichlorophenol manufacture was hazardous; ICMESA nevertheless continued to operate the plant in a heavily populated area and did not inform local health officials and emergency response personnel of the hazards either before or immediately after the accident. A design that allowed accidentally released toxins to be vented outside the factory reduced risk to workers in the plant at the expense of the population at large.

In the weeks following the accidents, about five hundred people were treated for symptoms of acute poisoning that included chloracne and liver and kidney malfunction. No immediate human fatalities were traceable to the accident. Livestock in open fields bore the full brunt of the toxic cloud, and those animals that did not succumb to initial toxic effects were destroyed. Poultry, wild birds, and cats proved particularly susceptible.

Between July 26 and August 2, the 730 inhabitants living in the most polluted zone near the factory, where soil concentrations of dioxin exceeded .01 parts per million, were evacuated. On August 28, 1976, the regional council of Lombardy appointed a commission to develop a decontamination plan and to work with regional health authorities to monitor the affected population.

Effects on pregnant women were of particular concern, since dioxins had been shown in laboratory experiments to be teratogenic in mice and were suspected of having increased the incidence of spontaneous abortions and birth defects in rural Vietnamese populations exposed to herbicides. Pregnant women were evacuated from the entire contaminated area, and the Italian government, despite opposition from the Vatican, gave permission for women from the Seveso area to obtain therapeutic abortions. In the four months following the incident, there were 183 deliveries, fifty-one spontaneous abortions, and twenty-eight therapeutic abortions among women exposed to dioxin. Although the rate of spontaneous abortions was higher than normal, there did not seem to be a significant rise in birth defects. Only years of monitoring would show the long-term effects of fetal and childhood exposure to a toxin such as dioxin. Eventually, for example, childhood dioxin exposure became suspected of being a factor in development of endometriosis in later life.





Decontamination of a dioxin-contaminated area was a massive undertaking, since dioxins are chemically stable compounds with an exceedingly slow rate of spontaneous breakdown. Options explored for decontamination of the Seveso area included incineration, photo degradation by ultraviolet light, degradation by ozone and gamma rays, solvent extraction, and chemical dechlorination. Most of these methods involved removing soil, building rubble, and the dismantled chemical factory itself to another location. Ultimately, it was judged to be less costly and less hazardous to the cleanup personnel to remove all soil and debris exceeding the limits set by the Lombardy regional government—10 nanograms per square meter (ng/m2) for building interiors, 750 ng/m2 for agricultural land, and 5,000 ng/m2 for nonagricultural land—to a central location, where it was buried in concrete and plastic-lined pits. The factory itself was dismantled, with stringent measures taken to ensure that the dismantling process did not release further dioxin into the environment. The decontamination process was hampered and partially undermined by the local residents, who resented the consequent disruptions to life and tended to ignore restrictions on their movements.

The exposed population was monitored for possible dioxin-related illnesses. From an epidemiologist’s point of view, the Seveso area provided an excellent laboratory for the study of the effects of dioxin exposure on human health, since the levels of exposure were known with some precision and the health status of the population before and after the accident was relatively easy to document (95 percent of the individuals exposed in 1976 still resided in Lombardy in 1986). A study of cancer incidence in Lombardy in the ten years after the accident illustrated the ambiguous results obtained from the monitoring efforts. Rates for all cancers were slightly higher for males than for females in the zone near the factory; the differences were, however, barely statistically significant. Pancreatic cancer, a relatively rare but lethal disease, was dramatically more common among women exposed to dioxin; on the other hand, the more common form of breast cancer was significantly less common among exposed women than in Lombardy as a whole. In general, the statistics suggested that measures taken to evacuate and decontaminate the area were effective. Although high by industrial standards, the dioxin levels in Seveso were orders of magnitude lower than those shown to produce cancer and birth defects in laboratory animals.


The 1976 Seveso dioxin explosion was a dramatic illustration of the dangers of manufacturing processes involving chlorinated hydrocarbons to populations living near chemical plants. The accident led to the implementation of more stringent controls on trichlorophenol manufacture in many industrialized countries. The event also inadvertently provided a laboratory for testing methods for neutralizing toxic wastes and for studying the long-term effects of a toxin on a population.

Dioxins belong to a class of chemicals known as chlorinated hydrocarbons, in which one or more of the hydrogen atoms in the basic hydrocarbon framework is replaced by a chlorine atom. In general, substituting chlorine for hydrogen in a biologically active organic molecule results in a compound with the capacity to disrupt metabolic processes, which makes chlorinated hydrocarbons effective as pesticides such as dichloro-diphenyl-trichloroethane (DDT), herbicides such as 2,4-dichlorophenoxyacetic acid (2,4-D), and disinfectants such as hexachlorophene. The high degree of chemical stability in chlorinated hydrocarbons is at once an attractive feature and a pitfall. The chemicals do not break down in storage and, once applied, continue to act for a long time; at the same time, they tend to persist and build up in the environment. Typically, they are not broken down or excreted by an organism that ingests them but are instead incorporated into fat reserves. They thus become concentrated in the food chain and are more dangerous to predators than to herbivores.

Polychlorinated biphenyls Polychlorinated biphenyls (PCBs) PCBs are chlorinated hydrocarbons formed from two linked benzene rings; dioxins are PCBs in which the linkage between the rings consists of two oxygen atoms. Theoretically, there are seventy-five possible chlorobenzoparadioxins, depending on the position and number of the chlorine atoms. Dioxins themselves have no commercial use. They are produced as by-products in chemical reactions employing trichlorophenol and are most likely to occur as a result of lax standards or a breakdown of the manufacturing process.

Dioxins were implicated in the controversy and litigation concerning Agent Orange, an herbicide used extensively during the Vietnam War. Vietnam War (1959-1975) Agent Orange, Agent Orange a toxic and persistent mixture of 2,4-D and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), was contaminated with dioxins to varying degrees. Massive amounts of Agent Orange were sprayed in Vietnam but subsequently withdrawn from general agricultural use in Europe and the United States. In 1974, the U.S. National Academy of Sciences published a report summarizing the evidence for direct adverse effects on the health of Vietnamese villagers in areas that had been subjected to heavy herbicide use; the report concluded that there was no conclusive evidence for the herbicide having caused deaths or birth defects, but the report also included reliable eyewitness testimony of deaths and illness among children exposed to the herbicides.

U.S. military personnel were also at times exposed to high levels of herbicide, which led to a long and bitter battle between Vietnam veterans and the U.S. Veterans Administration concerning whether illnesses developing years after exposure could be attributed to Agent Orange and be considered service-related disabilities. The medical follow-up data from Seveso were used in these cases and others that involved dioxin exposure and liability. The Seveso incident provided a useful comparison because it involved a relatively uniform population as regarded economic status and ethnic composition.

The case of American veterans exposed to Agent Orange was complex. A large body of anecdotal and case history evidence established, at least in the popular imagination, that ill health among Vietnam veterans was attributable to dioxin exposure, but the results of controlled epidemiological studies were inconclusive. Long-term monitoring of 1,257 Vietnam veterans who had been responsible for Project Ranch Hand, the actual delivery of herbicides—that is, the veterans most likely to have been exposed to dioxin—showed no greater mortality, cancer morbidity, or reported birth defects among their children than among those of veterans not involved in herbicide application. A review by the Centers for Disease Control in Atlanta of the 323,421 live births in the Atlanta area between 1968 and 1984 turned up the same proportion of birth defects among children of Vietnam veterans as among the general population. Nothing was, however, known about levels of dioxin exposure to individuals among the ground troops in areas of heavy herbicide use, who may have been exposed to higher levels of dioxin than those involved with Project Ranch Hand.

In 1984, Dow Chemical Company, Dow Chemical Company the manufacturer of Agent Orange, settled a class-action suit brought by Vietnam veterans exposed to the chemical and awarded an out-of-court settlement of $180 million (including attorneys’ fees) to 200,000 veterans and their survivors and dependents for conditions ranging from vaguely defined ill health to total disability and death.

Long-term damage to the health of residents of the most contaminated areas in Southeast Asia did not receive the same amount of publicity as that to the U.S. military personnel, although exposure to these areas was not of limited duration but continued for as long as the toxins persisted in the environment. Tetrachlorodibenzopara-dioxin Disasters;industrial Ecological disasters Dioxins

Further Reading
  • citation-type="booksimple"

    xlink:type="simple">Ballarin-Denti, A., et al., eds. Chemistry, Man and Environment: The Seveso Accident Twenty Years On—Monitoring, Epidemiology, and Remediation. New York: Elsevier, 1999. Assesses the current situation at Seveso since the accident and assembles new scientific research in the field.
  • citation-type="booksimple"

    xlink:type="simple">Cattabini, Flaminio, A. Cavallero, and G. Galli, eds. Dioxin: Toxicological and Chemical Aspects. New York: Spectrum Press, 1978. Presents the results of a conference on dioxin held in Milan, Italy, in 1976 in direct response to the Seveso incident, which is described in detail in the introduction. Gives extensive laboratory and field evidence of adverse health effects of dioxin exposure, as well as methods for assay and decontamination.
  • citation-type="booksimple"

    xlink:type="simple">Gough, Michael. Dioxin, Agent Orange: The Facts. New York: Plenum Press, 1986. The author, who directed research on Agent Orange for the Division of Health and Life Sciences at the Congressional Office of Technology, gives laboratory and epidemiological evidence for the adverse health effects of dioxin, principally in Vietnam veterans exposed to the herbicide. Summarizes evidence used to support the U.S. government case in litigation (and, incidentally, that of private companies responsible for dioxin exposure) that dioxin in the environment has not been shown to have negative effects on human health.
  • citation-type="booksimple"

    xlink:type="simple">Hay, Alstair. “Toxic Cloud over Seveso.” Nature 262 (1976): 636-638. Describes the immediate effects of the Seveso dioxin disaster, catalogs previous dioxin accidents, and provides evidence for a cover-up on the part of ICMESA officials. Questions whether trichlorophenol should be manufactured at all, considering the hazards involved.
  • citation-type="booksimple"

    xlink:type="simple">Mitchell, James Kenneth. Long Road to Recovery: Community Responses to Industrial Disaster. New York: United Nations University Press, 1996. Addresses major industrial disasters that occurred between 1949 and 1989. Emphasizes the need for long-term postdisaster assessments.
  • citation-type="booksimple"

    xlink:type="simple">Pesatori, A. C., et al. “Cancer Morbidity in the Seveso Area, 1976-1986.” Chemosphere 25 (1992): 209-212. Documents the results of long-term monitoring of the Seveso population and illustrates the uncertainty of epidemiological studies even in a situation where the variables are comparatively well defined.
  • citation-type="booksimple"

    xlink:type="simple">Rappe, Christopher, Gangadhar Choudhary, and Lawrence H. Keith, eds. Chlorinated Dioxins and Dibenzofurans in Perspective. Chelsea, Mich.: Lewis, 1986. Collection of articles on various aspects of dioxin research, including laboratory studies of toxicity, epidemiology, and environmental effects. Chapter 9 deals specifically with the cleanup following the Seveso accident.
  • citation-type="booksimple"

    xlink:type="simple">Whiteside, Thomas. The Pendulum and the Toxic Cloud: The Course of Dioxin Contamination. New Haven, Conn.: Yale University Press, 1979. Journalist’s account of dioxin contamination, approximately half of it devoted to the Seveso explosion. Includes interviews with local inhabitants and officials and discusses the political aspects of allowing a poorly regulated factory producing trichlorophenol to operate in a populated area. Appendixes summarize the results of animal experiments on dioxin toxicity.

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